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18837 | <!doctype html>
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<title>About this Documentation | Node.js v4.8.2 Manual & Documentation</title>
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<h1>Node.js v4.8.2 Documentation</h1>
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<div id="toc">
<h2>Table of Contents</h2>
<ul>
<li><span class="stability_undefined"><a href="#documentation_about_this_documentation">About this Documentation</a></span><ul>
<li><span class="stability_undefined"><a href="#documentation_stability_index">Stability Index</a></span></li>
<li><span class="stability_1"><a href="#documentation_json_output">JSON Output</a></span></li>
<li><span class="stability_undefined"><a href="#documentation_syscalls_and_man_pages">Syscalls and man pages</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#synopsis_usage">Usage</a></span><ul>
<li><span class="stability_undefined"><a href="#synopsis_example">Example</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#addons_c_c_addons">C/C++ Addons</a></span><ul>
<li><span class="stability_undefined"><a href="#addons_hello_world">Hello world</a></span><ul>
<li><span class="stability_undefined"><a href="#addons_building">Building</a></span></li>
<li><span class="stability_undefined"><a href="#addons_linking_to_node_js_own_dependencies">Linking to Node.js' own dependencies</a></span></li>
<li><span class="stability_undefined"><a href="#addons_loading_addons_using_require">Loading Addons using require()</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#addons_native_abstractions_for_node_js">Native Abstractions for Node.js</a></span></li>
<li><span class="stability_undefined"><a href="#addons_addon_examples">Addon examples</a></span><ul>
<li><span class="stability_undefined"><a href="#addons_function_arguments">Function arguments</a></span></li>
<li><span class="stability_undefined"><a href="#addons_callbacks">Callbacks</a></span></li>
<li><span class="stability_undefined"><a href="#addons_object_factory">Object factory</a></span></li>
<li><span class="stability_undefined"><a href="#addons_function_factory">Function factory</a></span></li>
<li><span class="stability_undefined"><a href="#addons_wrapping_c_objects">Wrapping C++ objects</a></span></li>
<li><span class="stability_undefined"><a href="#addons_factory_of_wrapped_objects">Factory of wrapped objects</a></span></li>
<li><span class="stability_undefined"><a href="#addons_passing_wrapped_objects_around">Passing wrapped objects around</a></span></li>
<li><span class="stability_undefined"><a href="#addons_atexit_hooks">AtExit hooks</a></span><ul>
<li><span class="stability_undefined"><a href="#addons_void_atexit_callback_args">void AtExit(callback, args)</a></span></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#assert_assert">Assert</a></span><ul>
<li><span class="stability_undefined"><a href="#assert_assert_value_message">assert(value[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_deepequal_actual_expected_message">assert.deepEqual(actual, expected[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_deepstrictequal_actual_expected_message">assert.deepStrictEqual(actual, expected[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_doesnotthrow_block_error_message">assert.doesNotThrow(block[, error][, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_equal_actual_expected_message">assert.equal(actual, expected[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_fail_actual_expected_message_operator">assert.fail(actual, expected, message, operator)</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_iferror_value">assert.ifError(value)</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_notdeepequal_actual_expected_message">assert.notDeepEqual(actual, expected[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_notdeepstrictequal_actual_expected_message">assert.notDeepStrictEqual(actual, expected[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_notequal_actual_expected_message">assert.notEqual(actual, expected[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_notstrictequal_actual_expected_message">assert.notStrictEqual(actual, expected[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_ok_value_message">assert.ok(value[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_strictequal_actual_expected_message">assert.strictEqual(actual, expected[, message])</a></span></li>
<li><span class="stability_undefined"><a href="#assert_assert_throws_block_error_message">assert.throws(block[, error][, message])</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#buffer_buffer">Buffer</a></span><ul>
<li><span class="stability_undefined"><a href="#buffer_buffer_from_buffer_alloc_and_buffer_allocunsafe"><code>Buffer.from()</code>, <code>Buffer.alloc()</code>, and <code>Buffer.allocUnsafe()</code></a></span><ul>
<li><span class="stability_undefined"><a href="#buffer_what_makes_buffer_allocunsafe_size_and_buffer_allocunsafeslow_size_unsafe">What makes <code>Buffer.allocUnsafe(size)</code> and <code>Buffer.allocUnsafeSlow(size)</code> "unsafe"?</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#buffer_buffers_and_character_encodings">Buffers and Character Encodings</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buffers_and_typedarray">Buffers and TypedArray</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buffers_and_es6_iteration">Buffers and ES6 iteration</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_the_zero_fill_buffers_command_line_option">The <code>--zero-fill-buffers</code> command line option</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_buffer">Class: Buffer</a></span><ul>
<li><span class="stability_undefined"><a href="#buffer_new_buffer_array">new Buffer(array)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_new_buffer_buffer">new Buffer(buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_new_buffer_arraybuffer">new Buffer(arrayBuffer)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_new_buffer_size">new Buffer(size)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_new_buffer_str_encoding">new Buffer(str[, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_alloc_size_fill_encoding">Class Method: Buffer.alloc(size[, fill[, encoding]])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_allocunsafe_size">Class Method: Buffer.allocUnsafe(size)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_allocunsafeslow_size">Class Method: Buffer.allocUnsafeSlow(size)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_bytelength_string_encoding">Class Method: Buffer.byteLength(string[, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_compare_buf1_buf2">Class Method: Buffer.compare(buf1, buf2)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_concat_list_totallength">Class Method: Buffer.concat(list[, totalLength])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_from_array">Class Method: Buffer.from(array)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_from_arraybuffer">Class Method: Buffer.from(arrayBuffer)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_from_buffer">Class Method: Buffer.from(buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_from_str_encoding">Class Method: Buffer.from(str[, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_isbuffer_obj">Class Method: Buffer.isBuffer(obj)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_method_buffer_isencoding_encoding">Class Method: Buffer.isEncoding(encoding)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_index">buf[index]</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_compare_otherbuffer">buf.compare(otherBuffer)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_copy_targetbuffer_targetstart_sourcestart_sourceend">buf.copy(targetBuffer[, targetStart[, sourceStart[, sourceEnd]]])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_entries">buf.entries()</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_equals_otherbuffer">buf.equals(otherBuffer)</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_fill_value_offset_end">buf.fill(value[, offset[, end]])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_indexof_value_byteoffset_encoding">buf.indexOf(value[, byteOffset][, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_keys">buf.keys()</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_length">buf.length</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readdoublebe_offset_noassert">buf.readDoubleBE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readdoublele_offset_noassert">buf.readDoubleLE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readfloatbe_offset_noassert">buf.readFloatBE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readfloatle_offset_noassert">buf.readFloatLE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readint8_offset_noassert">buf.readInt8(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readint16be_offset_noassert">buf.readInt16BE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readint16le_offset_noassert">buf.readInt16LE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readint32be_offset_noassert">buf.readInt32BE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readint32le_offset_noassert">buf.readInt32LE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readintbe_offset_bytelength_noassert">buf.readIntBE(offset, byteLength[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readintle_offset_bytelength_noassert">buf.readIntLE(offset, byteLength[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readuint8_offset_noassert">buf.readUInt8(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readuint16be_offset_noassert">buf.readUInt16BE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readuint16le_offset_noassert">buf.readUInt16LE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readuint32be_offset_noassert">buf.readUInt32BE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readuint32le_offset_noassert">buf.readUInt32LE(offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readuintbe_offset_bytelength_noassert">buf.readUIntBE(offset, byteLength[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_readuintle_offset_bytelength_noassert">buf.readUIntLE(offset, byteLength[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_slice_start_end">buf.slice([start[, end]])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_tostring_encoding_start_end">buf.toString([encoding[, start[, end]]])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_tojson">buf.toJSON()</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_values">buf.values()</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_write_string_offset_length_encoding">buf.write(string[, offset[, length]][, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writedoublebe_value_offset_noassert">buf.writeDoubleBE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writedoublele_value_offset_noassert">buf.writeDoubleLE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writefloatbe_value_offset_noassert">buf.writeFloatBE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writefloatle_value_offset_noassert">buf.writeFloatLE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeint8_value_offset_noassert">buf.writeInt8(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeint16be_value_offset_noassert">buf.writeInt16BE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeint16le_value_offset_noassert">buf.writeInt16LE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeint32be_value_offset_noassert">buf.writeInt32BE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeint32le_value_offset_noassert">buf.writeInt32LE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeintbe_value_offset_bytelength_noassert">buf.writeIntBE(value, offset, byteLength[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeintle_value_offset_bytelength_noassert">buf.writeIntLE(value, offset, byteLength[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeuint8_value_offset_noassert">buf.writeUInt8(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeuint16be_value_offset_noassert">buf.writeUInt16BE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeuint16le_value_offset_noassert">buf.writeUInt16LE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeuint32be_value_offset_noassert">buf.writeUInt32BE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeuint32le_value_offset_noassert">buf.writeUInt32LE(value, offset[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeuintbe_value_offset_bytelength_noassert">buf.writeUIntBE(value, offset, byteLength[, noAssert])</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_buf_writeuintle_value_offset_bytelength_noassert">buf.writeUIntLE(value, offset, byteLength[, noAssert])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#buffer_buffer_inspect_max_bytes">buffer.INSPECT_MAX_BYTES</a></span></li>
<li><span class="stability_undefined"><a href="#buffer_class_slowbuffer">Class: SlowBuffer</a></span><ul>
<li><span class="stability_undefined"><a href="#buffer_new_slowbuffer_size">new SlowBuffer(size)</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#child_process_child_process">Child Process</a></span><ul>
<li><span class="stability_undefined"><a href="#child_process_asynchronous_process_creation">Asynchronous Process Creation</a></span><ul>
<li><span class="stability_undefined"><a href="#child_process_spawning_bat_and_cmd_files_on_windows">Spawning <code>.bat</code> and <code>.cmd</code> files on Windows</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_process_exec_command_options_callback">child_process.exec(command[, options][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_process_execfile_file_args_options_callback">child_process.execFile(file[, args][, options][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_process_fork_modulepath_args_options">child_process.fork(modulePath[, args][, options])</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_process_spawn_command_args_options">child_process.spawn(command[, args][, options])</a></span><ul>
<li><span class="stability_undefined"><a href="#child_process_options_detached">options.detached</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_options_stdio">options.stdio</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#child_process_synchronous_process_creation">Synchronous Process Creation</a></span><ul>
<li><span class="stability_undefined"><a href="#child_process_child_process_execfilesync_file_args_options">child_process.execFileSync(file[, args][, options])</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_process_execsync_command_options">child_process.execSync(command[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_process_spawnsync_command_args_options">child_process.spawnSync(command[, args][, options])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#child_process_class_childprocess">Class: ChildProcess</a></span><ul>
<li><span class="stability_undefined"><a href="#child_process_event_close">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_event_disconnect">Event: 'disconnect'</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_event_error">Event: 'error'</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_event_exit">Event: 'exit'</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_event_message">Event: 'message'</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_connected">child.connected</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_disconnect">child.disconnect()</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_kill_signal">child.kill([signal])</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_pid">child.pid</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_send_message_sendhandle_callback">child.send(message[, sendHandle][, callback])</a></span><ul>
<li><span class="stability_undefined"><a href="#child_process_example_sending_a_server_object">Example: sending a server object</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_example_sending_a_socket_object">Example: sending a socket object</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#child_process_child_stderr">child.stderr</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_stdin">child.stdin</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_stdio">child.stdio</a></span></li>
<li><span class="stability_undefined"><a href="#child_process_child_stdout">child.stdout</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#cluster_cluster">Cluster</a></span><ul>
<li><span class="stability_undefined"><a href="#cluster_how_it_works">How It Works</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_class_worker">Class: Worker</a></span><ul>
<li><span class="stability_undefined"><a href="#cluster_event_disconnect">Event: 'disconnect'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_error">Event: 'error'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_exit">Event: 'exit'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_listening">Event: 'listening'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_message">Event: 'message'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_online">Event: 'online'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_worker_disconnect">worker.disconnect()</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_worker_id">worker.id</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_worker_isconnected">worker.isConnected()</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_worker_isdead">worker.isDead()</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_worker_kill_signal_sigterm">worker.kill([signal='SIGTERM'])</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_worker_process">worker.process</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_worker_send_message_sendhandle_callback">worker.send(message[, sendHandle][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_worker_suicide">worker.suicide</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#cluster_event_disconnect_1">Event: 'disconnect'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_exit_1">Event: 'exit'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_fork">Event: 'fork'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_listening_1">Event: 'listening'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_message_1">Event: 'message'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_online_1">Event: 'online'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_event_setup">Event: 'setup'</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_disconnect_callback">cluster.disconnect([callback])</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_fork_env">cluster.fork([env])</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_ismaster">cluster.isMaster</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_isworker">cluster.isWorker</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_schedulingpolicy">cluster.schedulingPolicy</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_settings">cluster.settings</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_setupmaster_settings">cluster.setupMaster([settings])</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_worker">cluster.worker</a></span></li>
<li><span class="stability_undefined"><a href="#cluster_cluster_workers">cluster.workers</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#cli_command_line_options">Command Line Options</a></span><ul>
<li><span class="stability_undefined"><a href="#cli_synopsis">Synopsis</a></span></li>
<li><span class="stability_undefined"><a href="#cli_options">Options</a></span><ul>
<li><span class="stability_undefined"><a href="#cli_v_version"><code>-v</code>, <code>--version</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_h_help"><code>-h</code>, <code>--help</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_e_eval_script"><code>-e</code>, <code>--eval "script"</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_p_print_script"><code>-p</code>, <code>--print "script"</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_c_check"><code>-c</code>, <code>--check</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_i_interactive"><code>-i</code>, <code>--interactive</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_r_require_module"><code>-r</code>, <code>--require module</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_no_deprecation"><code>--no-deprecation</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_trace_deprecation"><code>--trace-deprecation</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_throw_deprecation"><code>--throw-deprecation</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_trace_sync_io"><code>--trace-sync-io</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_zero_fill_buffers"><code>--zero-fill-buffers</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_track_heap_objects"><code>--track-heap-objects</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_prof_process"><code>--prof-process</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_v8_options"><code>--v8-options</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_tls_cipher_list_list"><code>--tls-cipher-list=list</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_enable_fips"><code>--enable-fips</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_force_fips"><code>--force-fips</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_icu_data_dir_file"><code>--icu-data-dir=file</code></a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#cli_environment_variables">Environment Variables</a></span><ul>
<li><span class="stability_undefined"><a href="#cli_node_debug_module"><code>NODE_DEBUG=module[,…]</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_node_path_path"><code>NODE_PATH=path[:…]</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_node_disable_colors_1"><code>NODE_DISABLE_COLORS=1</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_node_icu_data_file"><code>NODE_ICU_DATA=file</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_node_repl_history_file"><code>NODE_REPL_HISTORY=file</code></a></span></li>
<li><span class="stability_undefined"><a href="#cli_node_extra_ca_certs_file"><code>NODE_EXTRA_CA_CERTS=file</code></a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#console_console">Console</a></span><ul>
<li><span class="stability_undefined"><a href="#console_asynchronous_vs_synchronous_consoles">Asynchronous vs Synchronous Consoles</a></span></li>
<li><span class="stability_undefined"><a href="#console_class_console">Class: Console</a></span><ul>
<li><span class="stability_undefined"><a href="#console_new_console_stdout_stderr">new Console(stdout[, stderr])</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_assert_value_message">console.assert(value[, message][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_dir_obj_options">console.dir(obj[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_error_data">console.error([data][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_info_data">console.info([data][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_log_data">console.log([data][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_time_label">console.time(label)</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_timeend_label">console.timeEnd(label)</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_trace_message">console.trace(message[, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#console_console_warn_data">console.warn([data][, ...])</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#crypto_crypto">Crypto</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_class_certificate">Class: Certificate</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_new_crypto_certificate">new crypto.Certificate()</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_certificate_exportchallenge_spkac">certificate.exportChallenge(spkac)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_certificate_exportpublickey_spkac">certificate.exportPublicKey(spkac)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_certificate_verifyspkac_spkac">certificate.verifySpkac(spkac)</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_class_cipher">Class: Cipher</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_cipher_final_output_encoding">cipher.final([output_encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_cipher_setaad_buffer">cipher.setAAD(buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_cipher_getauthtag">cipher.getAuthTag()</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_cipher_setautopadding_auto_padding_true">cipher.setAutoPadding(auto_padding=true)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_cipher_update_data_input_encoding_output_encoding">cipher.update(data[, input_encoding][, output_encoding])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_class_decipher">Class: Decipher</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_decipher_final_output_encoding">decipher.final([output_encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_decipher_setaad_buffer">decipher.setAAD(buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_decipher_setauthtag_buffer">decipher.setAuthTag(buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_decipher_setautopadding_auto_padding_true">decipher.setAutoPadding(auto_padding=true)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_decipher_update_data_input_encoding_output_encoding">decipher.update(data[, input_encoding][, output_encoding])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_class_diffiehellman">Class: DiffieHellman</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_computesecret_other_public_key_input_encoding_output_encoding">diffieHellman.computeSecret(other_public_key[, input_encoding][, output_encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_generatekeys_encoding">diffieHellman.generateKeys([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_getgenerator_encoding">diffieHellman.getGenerator([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_getprime_encoding">diffieHellman.getPrime([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_getprivatekey_encoding">diffieHellman.getPrivateKey([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_getpublickey_encoding">diffieHellman.getPublicKey([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_setprivatekey_private_key_encoding">diffieHellman.setPrivateKey(private_key[, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_setpublickey_public_key_encoding">diffieHellman.setPublicKey(public_key[, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_diffiehellman_verifyerror">diffieHellman.verifyError</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_class_ecdh">Class: ECDH</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_ecdh_computesecret_other_public_key_input_encoding_output_encoding">ecdh.computeSecret(other_public_key[, input_encoding][, output_encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_ecdh_generatekeys_encoding_format">ecdh.generateKeys([encoding[, format]])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_ecdh_getprivatekey_encoding">ecdh.getPrivateKey([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_ecdh_getpublickey_encoding_format">ecdh.getPublicKey([encoding[, format]])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_ecdh_setprivatekey_private_key_encoding">ecdh.setPrivateKey(private_key[, encoding])</a></span></li>
<li><span class="stability_0"><a href="#crypto_ecdh_setpublickey_public_key_encoding">ecdh.setPublicKey(public_key[, encoding])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_class_hash">Class: Hash</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_hash_digest_encoding">hash.digest([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_hash_update_data_input_encoding">hash.update(data[, input_encoding])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_class_hmac">Class: Hmac</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_hmac_digest_encoding">hmac.digest([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_hmac_update_data_input_encoding">hmac.update(data[, input_encoding])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_class_sign">Class: Sign</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_sign_sign_private_key_output_format">sign.sign(private_key[, output_format])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_sign_update_data_input_encoding">sign.update(data[, input_encoding])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_class_verify">Class: Verify</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_verifier_update_data_input_encoding">verifier.update(data[, input_encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_verifier_verify_object_signature_signature_format">verifier.verify(object, signature[, signature_format])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_crypto_module_methods_and_properties"><code>crypto</code> module methods and properties</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_crypto_default_encoding">crypto.DEFAULT_ENCODING</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createcipher_algorithm_password">crypto.createCipher(algorithm, password)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createcipheriv_algorithm_key_iv">crypto.createCipheriv(algorithm, key, iv)</a></span></li>
<li><span class="stability_0"><a href="#crypto_crypto_createcredentials_details">crypto.createCredentials(details)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createdecipher_algorithm_password">crypto.createDecipher(algorithm, password)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createdecipheriv_algorithm_key_iv">crypto.createDecipheriv(algorithm, key, iv)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_creatediffiehellman_prime_prime_encoding_generator_generator_encoding">crypto.createDiffieHellman(prime[, prime_encoding][, generator][, generator_encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_creatediffiehellman_prime_length_generator">crypto.createDiffieHellman(prime_length[, generator])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createecdh_curve_name">crypto.createECDH(curve_name)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createhash_algorithm">crypto.createHash(algorithm)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createhmac_algorithm_key">crypto.createHmac(algorithm, key)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createsign_algorithm">crypto.createSign(algorithm)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_createverify_algorithm">crypto.createVerify(algorithm)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_getciphers">crypto.getCiphers()</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_getcurves">crypto.getCurves()</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_getdiffiehellman_group_name">crypto.getDiffieHellman(group_name)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_gethashes">crypto.getHashes()</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_pbkdf2_password_salt_iterations_keylen_digest_callback">crypto.pbkdf2(password, salt, iterations, keylen[, digest], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_pbkdf2sync_password_salt_iterations_keylen_digest">crypto.pbkdf2Sync(password, salt, iterations, keylen[, digest])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_privatedecrypt_private_key_buffer">crypto.privateDecrypt(private_key, buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_privateencrypt_private_key_buffer">crypto.privateEncrypt(private_key, buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_publicdecrypt_public_key_buffer">crypto.publicDecrypt(public_key, buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_publicencrypt_public_key_buffer">crypto.publicEncrypt(public_key, buffer)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_randombytes_size_callback">crypto.randomBytes(size[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_crypto_setengine_engine_flags">crypto.setEngine(engine[, flags])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#crypto_notes">Notes</a></span><ul>
<li><span class="stability_undefined"><a href="#crypto_legacy_streams_api_pre_node_js_v0_10">Legacy Streams API (pre Node.js v0.10)</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_recent_ecdh_changes">Recent ECDH Changes</a></span></li>
<li><span class="stability_undefined"><a href="#crypto_support_for_weak_or_compromised_algorithms">Support for weak or compromised algorithms</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#debugger_debugger">Debugger</a></span><ul>
<li><span class="stability_undefined"><a href="#debugger_watchers">Watchers</a></span></li>
<li><span class="stability_undefined"><a href="#debugger_command_reference">Command reference</a></span><ul>
<li><span class="stability_undefined"><a href="#debugger_stepping">Stepping</a></span></li>
<li><span class="stability_undefined"><a href="#debugger_breakpoints">Breakpoints</a></span></li>
<li><span class="stability_undefined"><a href="#debugger_information">Information</a></span></li>
<li><span class="stability_undefined"><a href="#debugger_execution_control">Execution control</a></span></li>
<li><span class="stability_undefined"><a href="#debugger_various">Various</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#debugger_advanced_usage">Advanced Usage</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#dgram_udp_datagram_sockets">UDP / Datagram Sockets</a></span><ul>
<li><span class="stability_undefined"><a href="#dgram_class_dgram_socket">Class: dgram.Socket</a></span><ul>
<li><span class="stability_undefined"><a href="#dgram_event_close">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_event_error">Event: 'error'</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_event_listening">Event: 'listening'</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_event_message">Event: 'message'</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_addmembership_multicastaddress_multicastinterface">socket.addMembership(multicastAddress[, multicastInterface])</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_address">socket.address()</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_bind_port_address_callback">socket.bind([port][, address][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_bind_options_callback">socket.bind(options[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_close_callback">socket.close([callback])</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_dropmembership_multicastaddress_multicastinterface">socket.dropMembership(multicastAddress[, multicastInterface])</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_send_buf_offset_length_port_address_callback">socket.send(buf, offset, length, port, address[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_setbroadcast_flag">socket.setBroadcast(flag)</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_setmulticastloopback_flag">socket.setMulticastLoopback(flag)</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_setmulticastttl_ttl">socket.setMulticastTTL(ttl)</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_setttl_ttl">socket.setTTL(ttl)</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_ref">socket.ref()</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_socket_unref">socket.unref()</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_change_to_asynchronous_socket_bind_behavior">Change to asynchronous <code>socket.bind()</code> behavior</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#dgram_dgram_module_functions"><code>dgram</code> module functions</a></span><ul>
<li><span class="stability_undefined"><a href="#dgram_dgram_createsocket_options_callback">dgram.createSocket(options[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#dgram_dgram_createsocket_type_callback">dgram.createSocket(type[, callback])</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#dns_dns">DNS</a></span><ul>
<li><span class="stability_undefined"><a href="#dns_dns_getservers">dns.getServers()</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_lookup_hostname_options_callback">dns.lookup(hostname[, options], callback)</a></span><ul>
<li><span class="stability_undefined"><a href="#dns_supported_getaddrinfo_flags">Supported getaddrinfo flags</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#dns_dns_lookupservice_address_port_callback">dns.lookupService(address, port, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolve_hostname_rrtype_callback">dns.resolve(hostname[, rrtype], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolve4_hostname_callback">dns.resolve4(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolve6_hostname_callback">dns.resolve6(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolvecname_hostname_callback">dns.resolveCname(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolvemx_hostname_callback">dns.resolveMx(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolvenaptr_hostname_callback">dns.resolveNaptr(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolvens_hostname_callback">dns.resolveNs(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolvesoa_hostname_callback">dns.resolveSoa(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolvesrv_hostname_callback">dns.resolveSrv(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolvetxt_hostname_callback">dns.resolveTxt(hostname, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_reverse_ip_callback">dns.reverse(ip, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_setservers_servers">dns.setServers(servers)</a></span></li>
<li><span class="stability_undefined"><a href="#dns_error_codes">Error codes</a></span></li>
<li><span class="stability_undefined"><a href="#dns_implementation_considerations">Implementation considerations</a></span><ul>
<li><span class="stability_undefined"><a href="#dns_dns_lookup"><code>dns.lookup()</code></a></span></li>
<li><span class="stability_undefined"><a href="#dns_dns_resolve_dns_resolve_and_dns_reverse"><code>dns.resolve()</code>, <code>dns.resolve*()</code> and <code>dns.reverse()</code></a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_0"><a href="#domain_domain">Domain</a></span><ul>
<li><span class="stability_undefined"><a href="#domain_warning_don_t_ignore_errors">Warning: Don't Ignore Errors!</a></span></li>
<li><span class="stability_undefined"><a href="#domain_additions_to_error_objects">Additions to Error objects</a></span></li>
<li><span class="stability_undefined"><a href="#domain_implicit_binding">Implicit Binding</a></span></li>
<li><span class="stability_undefined"><a href="#domain_explicit_binding">Explicit Binding</a></span></li>
<li><span class="stability_undefined"><a href="#domain_domain_create">domain.create()</a></span></li>
<li><span class="stability_undefined"><a href="#domain_class_domain">Class: Domain</a></span><ul>
<li><span class="stability_undefined"><a href="#domain_domain_run_fn_arg">domain.run(fn[, arg][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#domain_domain_members">domain.members</a></span></li>
<li><span class="stability_undefined"><a href="#domain_domain_add_emitter">domain.add(emitter)</a></span></li>
<li><span class="stability_undefined"><a href="#domain_domain_remove_emitter">domain.remove(emitter)</a></span></li>
<li><span class="stability_undefined"><a href="#domain_domain_bind_callback">domain.bind(callback)</a></span><ul>
<li><span class="stability_undefined"><a href="#domain_example">Example</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#domain_domain_intercept_callback">domain.intercept(callback)</a></span><ul>
<li><span class="stability_undefined"><a href="#domain_example_1">Example</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#domain_domain_enter">domain.enter()</a></span></li>
<li><span class="stability_undefined"><a href="#domain_domain_exit">domain.exit()</a></span></li>
<li><span class="stability_0"><a href="#domain_domain_dispose">domain.dispose()</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#errors_errors">Errors</a></span><ul>
<li><span class="stability_undefined"><a href="#errors_error_propagation_and_interception">Error Propagation and Interception</a></span><ul>
<li><span class="stability_undefined"><a href="#errors_node_js_style_callbacks">Node.js style callbacks</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#errors_class_error">Class: Error</a></span><ul>
<li><span class="stability_undefined"><a href="#errors_new_error_message">new Error(message)</a></span></li>
<li><span class="stability_undefined"><a href="#errors_error_capturestacktrace_targetobject_constructoropt">Error.captureStackTrace(targetObject[, constructorOpt])</a></span></li>
<li><span class="stability_undefined"><a href="#errors_error_stacktracelimit">Error.stackTraceLimit</a></span><ul>
<li><span class="stability_undefined"><a href="#errors_error_message">error.message</a></span></li>
<li><span class="stability_undefined"><a href="#errors_error_stack">error.stack</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#errors_class_rangeerror">Class: RangeError</a></span></li>
<li><span class="stability_undefined"><a href="#errors_class_referenceerror">Class: ReferenceError</a></span></li>
<li><span class="stability_undefined"><a href="#errors_class_syntaxerror">Class: SyntaxError</a></span></li>
<li><span class="stability_undefined"><a href="#errors_class_typeerror">Class: TypeError</a></span></li>
<li><span class="stability_undefined"><a href="#errors_exceptions_vs_errors">Exceptions vs. Errors</a></span></li>
<li><span class="stability_undefined"><a href="#errors_system_errors">System Errors</a></span><ul>
<li><span class="stability_undefined"><a href="#errors_class_system_error">Class: System Error</a></span><ul>
<li><span class="stability_undefined"><a href="#errors_error_code">error.code</a></span></li>
<li><span class="stability_undefined"><a href="#errors_error_errno">error.errno</a></span></li>
<li><span class="stability_undefined"><a href="#errors_error_syscall">error.syscall</a></span></li>
<li><span class="stability_undefined"><a href="#errors_error_path">error.path</a></span></li>
<li><span class="stability_undefined"><a href="#errors_error_address">error.address</a></span></li>
<li><span class="stability_undefined"><a href="#errors_error_port">error.port</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#errors_common_system_errors">Common System Errors</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#events_events">Events</a></span><ul>
<li><span class="stability_undefined"><a href="#events_passing_arguments_and_this_to_listeners">Passing arguments and <code>this</code> to listeners</a></span></li>
<li><span class="stability_undefined"><a href="#events_asynchronous_vs_synchronous">Asynchronous vs. Synchronous</a></span></li>
<li><span class="stability_undefined"><a href="#events_handling_events_only_once">Handling events only once</a></span></li>
<li><span class="stability_undefined"><a href="#events_error_events">Error events</a></span></li>
<li><span class="stability_undefined"><a href="#events_class_eventemitter">Class: EventEmitter</a></span><ul>
<li><span class="stability_undefined"><a href="#events_event_newlistener">Event: 'newListener'</a></span></li>
<li><span class="stability_undefined"><a href="#events_event_removelistener">Event: 'removeListener'</a></span></li>
<li><span class="stability_0"><a href="#events_eventemitter_listenercount_emitter_eventname">EventEmitter.listenerCount(emitter, eventName)</a></span></li>
<li><span class="stability_undefined"><a href="#events_eventemitter_defaultmaxlisteners">EventEmitter.defaultMaxListeners</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_addlistener_eventname_listener">emitter.addListener(eventName, listener)</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_emit_eventname_arg1_arg2">emitter.emit(eventName[, arg1][, arg2][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_getmaxlisteners">emitter.getMaxListeners()</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_listenercount_eventname">emitter.listenerCount(eventName)</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_listeners_eventname">emitter.listeners(eventName)</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_on_eventname_listener">emitter.on(eventName, listener)</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_once_eventname_listener">emitter.once(eventName, listener)</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_removealllisteners_eventname">emitter.removeAllListeners([eventName])</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_removelistener_eventname_listener">emitter.removeListener(eventName, listener)</a></span></li>
<li><span class="stability_undefined"><a href="#events_emitter_setmaxlisteners_n">emitter.setMaxListeners(n)</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#fs_file_system">File System</a></span><ul>
<li><span class="stability_undefined"><a href="#fs_class_fs_fswatcher">Class: fs.FSWatcher</a></span><ul>
<li><span class="stability_undefined"><a href="#fs_event_change">Event: 'change'</a></span></li>
<li><span class="stability_undefined"><a href="#fs_event_error">Event: 'error'</a></span></li>
<li><span class="stability_undefined"><a href="#fs_watcher_close">watcher.close()</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#fs_class_fs_readstream">Class: fs.ReadStream</a></span><ul>
<li><span class="stability_undefined"><a href="#fs_event_open">Event: 'open'</a></span></li>
<li><span class="stability_undefined"><a href="#fs_event_close">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#fs_readstream_path">readStream.path</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#fs_class_fs_stats">Class: fs.Stats</a></span><ul>
<li><span class="stability_undefined"><a href="#fs_stat_time_values">Stat Time Values</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#fs_class_fs_writestream">Class: fs.WriteStream</a></span><ul>
<li><span class="stability_undefined"><a href="#fs_event_open_1">Event: 'open'</a></span></li>
<li><span class="stability_undefined"><a href="#fs_event_close_1">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#fs_writestream_byteswritten">writeStream.bytesWritten</a></span></li>
<li><span class="stability_undefined"><a href="#fs_writestream_path">writeStream.path</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#fs_fs_access_path_mode_callback">fs.access(path[, mode], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_accesssync_path_mode">fs.accessSync(path[, mode])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_appendfile_file_data_options_callback">fs.appendFile(file, data[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_appendfilesync_file_data_options">fs.appendFileSync(file, data[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_chmod_path_mode_callback">fs.chmod(path, mode, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_chmodsync_path_mode">fs.chmodSync(path, mode)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_chown_path_uid_gid_callback">fs.chown(path, uid, gid, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_chownsync_path_uid_gid">fs.chownSync(path, uid, gid)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_close_fd_callback">fs.close(fd, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_closesync_fd">fs.closeSync(fd)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_createreadstream_path_options">fs.createReadStream(path[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_createwritestream_path_options">fs.createWriteStream(path[, options])</a></span></li>
<li><span class="stability_0"><a href="#fs_fs_exists_path_callback">fs.exists(path, callback)</a></span></li>
<li><span class="stability_0"><a href="#fs_fs_existssync_path">fs.existsSync(path)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fchmod_fd_mode_callback">fs.fchmod(fd, mode, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fchmodsync_fd_mode">fs.fchmodSync(fd, mode)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fchown_fd_uid_gid_callback">fs.fchown(fd, uid, gid, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fchownsync_fd_uid_gid">fs.fchownSync(fd, uid, gid)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fdatasync_fd_callback">fs.fdatasync(fd, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fdatasyncsync_fd">fs.fdatasyncSync(fd)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fstat_fd_callback">fs.fstat(fd, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fstatsync_fd">fs.fstatSync(fd)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fsync_fd_callback">fs.fsync(fd, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_fsyncsync_fd">fs.fsyncSync(fd)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_ftruncate_fd_len_callback">fs.ftruncate(fd, len, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_ftruncatesync_fd_len">fs.ftruncateSync(fd, len)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_futimes_fd_atime_mtime_callback">fs.futimes(fd, atime, mtime, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_futimessync_fd_atime_mtime">fs.futimesSync(fd, atime, mtime)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_lchmod_path_mode_callback">fs.lchmod(path, mode, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_lchmodsync_path_mode">fs.lchmodSync(path, mode)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_lchown_path_uid_gid_callback">fs.lchown(path, uid, gid, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_lchownsync_path_uid_gid">fs.lchownSync(path, uid, gid)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_link_srcpath_dstpath_callback">fs.link(srcpath, dstpath, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_linksync_srcpath_dstpath">fs.linkSync(srcpath, dstpath)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_lstat_path_callback">fs.lstat(path, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_lstatsync_path">fs.lstatSync(path)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_mkdir_path_mode_callback">fs.mkdir(path[, mode], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_mkdirsync_path_mode">fs.mkdirSync(path[, mode])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_mkdtemp_prefix_callback">fs.mkdtemp(prefix, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_mkdtempsync_template">fs.mkdtempSync(template)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_open_path_flags_mode_callback">fs.open(path, flags[, mode], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_opensync_path_flags_mode">fs.openSync(path, flags[, mode])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_read_fd_buffer_offset_length_position_callback">fs.read(fd, buffer, offset, length, position, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_readdir_path_callback">fs.readdir(path, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_readdirsync_path">fs.readdirSync(path)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_readfile_file_options_callback">fs.readFile(file[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_readfilesync_file_options">fs.readFileSync(file[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_readlink_path_callback">fs.readlink(path, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_readlinksync_path">fs.readlinkSync(path)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_realpath_path_cache_callback">fs.realpath(path[, cache], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_readsync_fd_buffer_offset_length_position">fs.readSync(fd, buffer, offset, length, position)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_realpathsync_path_cache">fs.realpathSync(path[, cache])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_rename_oldpath_newpath_callback">fs.rename(oldPath, newPath, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_renamesync_oldpath_newpath">fs.renameSync(oldPath, newPath)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_rmdir_path_callback">fs.rmdir(path, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_rmdirsync_path">fs.rmdirSync(path)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_stat_path_callback">fs.stat(path, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_statsync_path">fs.statSync(path)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_symlink_target_path_type_callback">fs.symlink(target, path[, type], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_symlinksync_target_path_type">fs.symlinkSync(target, path[, type])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_truncate_path_len_callback">fs.truncate(path, len, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_truncatesync_path_len">fs.truncateSync(path, len)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_unlink_path_callback">fs.unlink(path, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_unlinksync_path">fs.unlinkSync(path)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_unwatchfile_filename_listener">fs.unwatchFile(filename[, listener])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_utimes_path_atime_mtime_callback">fs.utimes(path, atime, mtime, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_utimessync_path_atime_mtime">fs.utimesSync(path, atime, mtime)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_watch_filename_options_listener">fs.watch(filename[, options][, listener])</a></span><ul>
<li><span class="stability_undefined"><a href="#fs_caveats">Caveats</a></span><ul>
<li><span class="stability_undefined"><a href="#fs_availability">Availability</a></span></li>
<li><span class="stability_undefined"><a href="#fs_inodes">Inodes</a></span></li>
<li><span class="stability_undefined"><a href="#fs_filename_argument">Filename Argument</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#fs_fs_watchfile_filename_options_listener">fs.watchFile(filename[, options], listener)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_write_fd_buffer_offset_length_position_callback">fs.write(fd, buffer, offset, length[, position], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_write_fd_data_position_encoding_callback">fs.write(fd, data[, position[, encoding]], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_writefile_file_data_options_callback">fs.writeFile(file, data[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_writefilesync_file_data_options">fs.writeFileSync(file, data[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_writesync_fd_buffer_offset_length_position">fs.writeSync(fd, buffer, offset, length[, position])</a></span></li>
<li><span class="stability_undefined"><a href="#fs_fs_writesync_fd_data_position_encoding">fs.writeSync(fd, data[, position[, encoding]])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#globals_global_objects">Global Objects</a></span><ul>
<li><span class="stability_undefined"><a href="#globals_class_buffer">Class: Buffer</a></span></li>
<li><span class="stability_undefined"><a href="#globals_dirname">__dirname</a></span></li>
<li><span class="stability_undefined"><a href="#globals_filename">__filename</a></span></li>
<li><span class="stability_undefined"><a href="#globals_clearimmediate_immediateobject">clearImmediate(immediateObject)</a></span></li>
<li><span class="stability_undefined"><a href="#globals_clearinterval_intervalobject">clearInterval(intervalObject)</a></span></li>
<li><span class="stability_undefined"><a href="#globals_cleartimeout_timeoutobject">clearTimeout(timeoutObject)</a></span></li>
<li><span class="stability_undefined"><a href="#globals_console">console</a></span></li>
<li><span class="stability_undefined"><a href="#globals_exports">exports</a></span></li>
<li><span class="stability_undefined"><a href="#globals_global">global</a></span></li>
<li><span class="stability_undefined"><a href="#globals_module">module</a></span></li>
<li><span class="stability_undefined"><a href="#globals_process">process</a></span></li>
<li><span class="stability_undefined"><a href="#globals_require">require()</a></span><ul>
<li><span class="stability_undefined"><a href="#globals_require_cache">require.cache</a></span></li>
<li><span class="stability_0"><a href="#globals_require_extensions">require.extensions</a></span></li>
<li><span class="stability_undefined"><a href="#globals_require_resolve">require.resolve()</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#globals_setimmediate_callback_arg">setImmediate(callback[, arg][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#globals_setinterval_callback_delay_arg">setInterval(callback, delay[, arg][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#globals_settimeout_callback_delay_arg">setTimeout(callback, delay[, arg][, ...])</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#http_http">HTTP</a></span><ul>
<li><span class="stability_undefined"><a href="#http_class_http_agent">Class: http.Agent</a></span><ul>
<li><span class="stability_undefined"><a href="#http_new_agent_options">new Agent([options])</a></span></li>
<li><span class="stability_undefined"><a href="#http_agent_destroy">agent.destroy()</a></span></li>
<li><span class="stability_undefined"><a href="#http_agent_freesockets">agent.freeSockets</a></span></li>
<li><span class="stability_undefined"><a href="#http_agent_getname_options">agent.getName(options)</a></span></li>
<li><span class="stability_undefined"><a href="#http_agent_maxfreesockets">agent.maxFreeSockets</a></span></li>
<li><span class="stability_undefined"><a href="#http_agent_maxsockets">agent.maxSockets</a></span></li>
<li><span class="stability_undefined"><a href="#http_agent_requests">agent.requests</a></span></li>
<li><span class="stability_undefined"><a href="#http_agent_sockets">agent.sockets</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#http_class_http_clientrequest">Class: http.ClientRequest</a></span><ul>
<li><span class="stability_undefined"><a href="#http_event_abort">Event: 'abort'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_aborted">Event: 'aborted'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_connect">Event: 'connect'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_continue">Event: 'continue'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_response">Event: 'response'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_socket">Event: 'socket'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_upgrade">Event: 'upgrade'</a></span></li>
<li><span class="stability_undefined"><a href="#http_request_abort">request.abort()</a></span></li>
<li><span class="stability_undefined"><a href="#http_request_aborted">request.aborted</a></span></li>
<li><span class="stability_undefined"><a href="#http_request_end_data_encoding_callback">request.end([data][, encoding][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_request_flushheaders">request.flushHeaders()</a></span></li>
<li><span class="stability_undefined"><a href="#http_request_setnodelay_nodelay">request.setNoDelay([noDelay])</a></span></li>
<li><span class="stability_undefined"><a href="#http_request_setsocketkeepalive_enable_initialdelay">request.setSocketKeepAlive([enable][, initialDelay])</a></span></li>
<li><span class="stability_undefined"><a href="#http_request_settimeout_timeout_callback">request.setTimeout(timeout[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_request_write_chunk_encoding_callback">request.write(chunk[, encoding][, callback])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#http_class_http_server">Class: http.Server</a></span><ul>
<li><span class="stability_undefined"><a href="#http_event_checkcontinue">Event: 'checkContinue'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_clienterror">Event: 'clientError'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_close">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_connect_1">Event: 'connect'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_connection">Event: 'connection'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_request">Event: 'request'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_upgrade_1">Event: 'upgrade'</a></span></li>
<li><span class="stability_undefined"><a href="#http_server_close_callback">server.close([callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_server_listen_handle_callback">server.listen(handle[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_server_listen_path_callback">server.listen(path[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_server_listen_port_hostname_backlog_callback">server.listen([port][, hostname][, backlog][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_server_maxheaderscount">server.maxHeadersCount</a></span></li>
<li><span class="stability_undefined"><a href="#http_server_settimeout_msecs_callback">server.setTimeout(msecs, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#http_server_timeout">server.timeout</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#http_class_http_serverresponse">Class: http.ServerResponse</a></span><ul>
<li><span class="stability_undefined"><a href="#http_event_close_1">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_finish">Event: 'finish'</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_addtrailers_headers">response.addTrailers(headers)</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_end_data_encoding_callback">response.end([data][, encoding][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_finished">response.finished</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_getheader_name">response.getHeader(name)</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_headerssent">response.headersSent</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_removeheader_name">response.removeHeader(name)</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_senddate">response.sendDate</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_setheader_name_value">response.setHeader(name, value)</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_settimeout_msecs_callback">response.setTimeout(msecs, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_statuscode">response.statusCode</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_statusmessage">response.statusMessage</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_write_chunk_encoding_callback">response.write(chunk[, encoding][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_writecontinue">response.writeContinue()</a></span></li>
<li><span class="stability_undefined"><a href="#http_response_writehead_statuscode_statusmessage_headers">response.writeHead(statusCode[, statusMessage][, headers])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#http_class_http_incomingmessage">Class: http.IncomingMessage</a></span><ul>
<li><span class="stability_undefined"><a href="#http_event_aborted_1">Event: 'aborted'</a></span></li>
<li><span class="stability_undefined"><a href="#http_event_close_2">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_destroy_error">message.destroy([error])</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_headers">message.headers</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_httpversion">message.httpVersion</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_method">message.method</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_rawheaders">message.rawHeaders</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_rawtrailers">message.rawTrailers</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_settimeout_msecs_callback">message.setTimeout(msecs, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_statuscode">message.statusCode</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_statusmessage">message.statusMessage</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_socket">message.socket</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_trailers">message.trailers</a></span></li>
<li><span class="stability_undefined"><a href="#http_message_url">message.url</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#http_http_methods">http.METHODS</a></span></li>
<li><span class="stability_undefined"><a href="#http_http_status_codes">http.STATUS_CODES</a></span></li>
<li><span class="stability_0"><a href="#http_http_createclient_port_host">http.createClient([port][, host])</a></span></li>
<li><span class="stability_undefined"><a href="#http_http_createserver_requestlistener">http.createServer([requestListener])</a></span></li>
<li><span class="stability_undefined"><a href="#http_http_get_options_callback">http.get(options[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#http_http_globalagent">http.globalAgent</a></span></li>
<li><span class="stability_undefined"><a href="#http_http_request_options_callback">http.request(options[, callback])</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#https_https">HTTPS</a></span><ul>
<li><span class="stability_undefined"><a href="#https_class_https_agent">Class: https.Agent</a></span></li>
<li><span class="stability_undefined"><a href="#https_class_https_server">Class: https.Server</a></span><ul>
<li><span class="stability_undefined"><a href="#https_server_settimeout_msecs_callback">server.setTimeout(msecs, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#https_server_timeout">server.timeout</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#https_https_createserver_options_requestlistener">https.createServer(options[, requestListener])</a></span><ul>
<li><span class="stability_undefined"><a href="#https_server_close_callback">server.close([callback])</a></span></li>
<li><span class="stability_undefined"><a href="#https_server_listen_handle_callback">server.listen(handle[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#https_server_listen_path_callback">server.listen(path[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#https_server_listen_port_host_backlog_callback">server.listen(port[, host][, backlog][, callback])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#https_https_get_options_callback">https.get(options, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#https_https_globalagent">https.globalAgent</a></span></li>
<li><span class="stability_undefined"><a href="#https_https_request_options_callback">https.request(options, callback)</a></span></li>
</ul>
</li>
<li><span class="stability_3"><a href="#modules_modules">Modules</a></span><ul>
<li><span class="stability_undefined"><a href="#modules_accessing_the_main_module">Accessing the main module</a></span></li>
<li><span class="stability_undefined"><a href="#modules_addenda_package_manager_tips">Addenda: Package Manager Tips</a></span></li>
<li><span class="stability_undefined"><a href="#modules_all_together">All Together...</a></span></li>
<li><span class="stability_undefined"><a href="#modules_caching">Caching</a></span><ul>
<li><span class="stability_undefined"><a href="#modules_module_caching_caveats">Module Caching Caveats</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#modules_core_modules">Core Modules</a></span></li>
<li><span class="stability_undefined"><a href="#modules_cycles">Cycles</a></span></li>
<li><span class="stability_undefined"><a href="#modules_file_modules">File Modules</a></span></li>
<li><span class="stability_undefined"><a href="#modules_folders_as_modules">Folders as Modules</a></span></li>
<li><span class="stability_undefined"><a href="#modules_loading_from_node_modules_folders">Loading from <code>node_modules</code> Folders</a></span></li>
<li><span class="stability_undefined"><a href="#modules_loading_from_the_global_folders">Loading from the global folders</a></span></li>
<li><span class="stability_undefined"><a href="#modules_the_module_wrapper">The module wrapper</a></span></li>
<li><span class="stability_undefined"><a href="#modules_the_module_object">The <code>module</code> Object</a></span><ul>
<li><span class="stability_undefined"><a href="#modules_module_children">module.children</a></span></li>
<li><span class="stability_undefined"><a href="#modules_module_exports">module.exports</a></span><ul>
<li><span class="stability_undefined"><a href="#modules_exports_shortcut">exports shortcut</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#modules_module_filename">module.filename</a></span></li>
<li><span class="stability_undefined"><a href="#modules_module_id">module.id</a></span></li>
<li><span class="stability_undefined"><a href="#modules_module_loaded">module.loaded</a></span></li>
<li><span class="stability_undefined"><a href="#modules_module_parent">module.parent</a></span></li>
<li><span class="stability_undefined"><a href="#modules_module_require_id">module.require(id)</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#net_net">Net</a></span><ul>
<li><span class="stability_undefined"><a href="#net_class_net_server">Class: net.Server</a></span><ul>
<li><span class="stability_undefined"><a href="#net_event_close">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_connection">Event: 'connection'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_error">Event: 'error'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_listening">Event: 'listening'</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_address">server.address()</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_close_callback">server.close([callback])</a></span></li>
<li><span class="stability_0"><a href="#net_server_connections">server.connections</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_getconnections_callback">server.getConnections(callback)</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_listen_handle_backlog_callback">server.listen(handle[, backlog][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_listen_options_callback">server.listen(options[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_listen_path_backlog_callback">server.listen(path[, backlog][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_listen_port_hostname_backlog_callback">server.listen([port][, hostname][, backlog][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_maxconnections">server.maxConnections</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_ref">server.ref()</a></span></li>
<li><span class="stability_undefined"><a href="#net_server_unref">server.unref()</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#net_class_net_socket">Class: net.Socket</a></span><ul>
<li><span class="stability_undefined"><a href="#net_new_net_socket_options">new net.Socket([options])</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_close_1">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_connect">Event: 'connect'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_data">Event: 'data'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_drain">Event: 'drain'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_end">Event: 'end'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_error_1">Event: 'error'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_lookup">Event: 'lookup'</a></span></li>
<li><span class="stability_undefined"><a href="#net_event_timeout">Event: 'timeout'</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_address">socket.address()</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_buffersize">socket.bufferSize</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_bytesread">socket.bytesRead</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_byteswritten">socket.bytesWritten</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_connect_options_connectlistener">socket.connect(options[, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_connect_path_connectlistener">socket.connect(path[, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_connect_port_host_connectlistener">socket.connect(port[, host][, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_destroy">socket.destroy()</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_destroyed">socket.destroyed</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_end_data_encoding">socket.end([data][, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_localaddress">socket.localAddress</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_localport">socket.localPort</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_pause">socket.pause()</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_ref">socket.ref()</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_remoteaddress">socket.remoteAddress</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_remotefamily">socket.remoteFamily</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_remoteport">socket.remotePort</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_resume">socket.resume()</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_setencoding_encoding">socket.setEncoding([encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_setkeepalive_enable_initialdelay">socket.setKeepAlive([enable][, initialDelay])</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_setnodelay_nodelay">socket.setNoDelay([noDelay])</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_settimeout_timeout_callback">socket.setTimeout(timeout[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_unref">socket.unref()</a></span></li>
<li><span class="stability_undefined"><a href="#net_socket_write_data_encoding_callback">socket.write(data[, encoding][, callback])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#net_net_connect_options_connectlistener">net.connect(options[, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_connect_path_connectlistener">net.connect(path[, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_connect_port_host_connectlistener">net.connect(port[, host][, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_createconnection_options_connectlistener">net.createConnection(options[, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_createconnection_path_connectlistener">net.createConnection(path[, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_createconnection_port_host_connectlistener">net.createConnection(port[, host][, connectListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_createserver_options_connectionlistener">net.createServer([options][, connectionListener])</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_isip_input">net.isIP(input)</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_isipv4_input">net.isIPv4(input)</a></span></li>
<li><span class="stability_undefined"><a href="#net_net_isipv6_input">net.isIPv6(input)</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#os_os">OS</a></span><ul>
<li><span class="stability_undefined"><a href="#os_os_eol">os.EOL</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_arch">os.arch()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_cpus">os.cpus()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_endianness">os.endianness()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_freemem">os.freemem()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_homedir">os.homedir()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_hostname">os.hostname()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_loadavg">os.loadavg()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_networkinterfaces">os.networkInterfaces()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_platform">os.platform()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_release">os.release()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_tmpdir">os.tmpdir()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_totalmem">os.totalmem()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_type">os.type()</a></span></li>
<li><span class="stability_undefined"><a href="#os_os_uptime">os.uptime()</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#path_path">Path</a></span><ul>
<li><span class="stability_undefined"><a href="#path_path_basename_p_ext">path.basename(p[, ext])</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_delimiter">path.delimiter</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_dirname_p">path.dirname(p)</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_extname_p">path.extname(p)</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_format_pathobject">path.format(pathObject)</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_isabsolute_path">path.isAbsolute(path)</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_join_path1_path2">path.join([path1][, path2][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_normalize_p">path.normalize(p)</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_parse_pathstring">path.parse(pathString)</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_posix">path.posix</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_relative_from_to">path.relative(from, to)</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_resolve_from_to">path.resolve([from ...], to)</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_sep">path.sep</a></span></li>
<li><span class="stability_undefined"><a href="#path_path_win32">path.win32</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#process_process">Process</a></span><ul>
<li><span class="stability_undefined"><a href="#process_event_beforeexit">Event: 'beforeExit'</a></span></li>
<li><span class="stability_undefined"><a href="#process_event_exit">Event: 'exit'</a></span></li>
<li><span class="stability_undefined"><a href="#process_event_message">Event: 'message'</a></span></li>
<li><span class="stability_undefined"><a href="#process_event_rejectionhandled">Event: 'rejectionHandled'</a></span></li>
<li><span class="stability_undefined"><a href="#process_event_uncaughtexception">Event: 'uncaughtException'</a></span><ul>
<li><span class="stability_undefined"><a href="#process_warning_using_uncaughtexception_correctly">Warning: Using <code>'uncaughtException'</code> correctly</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#process_event_unhandledrejection">Event: 'unhandledRejection'</a></span></li>
<li><span class="stability_undefined"><a href="#process_exit_codes">Exit Codes</a></span></li>
<li><span class="stability_undefined"><a href="#process_signal_events">Signal Events</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_abort">process.abort()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_arch">process.arch</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_argv">process.argv</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_chdir_directory">process.chdir(directory)</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_config">process.config</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_connected">process.connected</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_cpuusage_previousvalue">process.cpuUsage([previousValue])</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_cwd">process.cwd()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_disconnect">process.disconnect()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_env">process.env</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_execargv">process.execArgv</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_execpath">process.execPath</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_exit_code">process.exit([code])</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_exitcode">process.exitCode</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_getegid">process.getegid()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_geteuid">process.geteuid()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_getgid">process.getgid()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_getgroups">process.getgroups()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_getuid">process.getuid()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_hrtime">process.hrtime()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_initgroups_user_extra_group">process.initgroups(user, extra_group)</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_kill_pid_signal">process.kill(pid[, signal])</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_mainmodule">process.mainModule</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_memoryusage">process.memoryUsage()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_nexttick_callback_arg">process.nextTick(callback[, arg][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_pid">process.pid</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_platform">process.platform</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_release">process.release</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_send_message_sendhandle_callback">process.send(message[, sendHandle][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_setegid_id">process.setegid(id)</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_seteuid_id">process.seteuid(id)</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_setgid_id">process.setgid(id)</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_setgroups_groups">process.setgroups(groups)</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_setuid_id">process.setuid(id)</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_stderr">process.stderr</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_stdin">process.stdin</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_stdout">process.stdout</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_title">process.title</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_umask_mask">process.umask([mask])</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_uptime">process.uptime()</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_version">process.version</a></span></li>
<li><span class="stability_undefined"><a href="#process_process_versions">process.versions</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#punycode_punycode">Punycode</a></span><ul>
<li><span class="stability_undefined"><a href="#punycode_punycode_decode_string">punycode.decode(string)</a></span></li>
<li><span class="stability_undefined"><a href="#punycode_punycode_encode_string">punycode.encode(string)</a></span></li>
<li><span class="stability_undefined"><a href="#punycode_punycode_toascii_domain">punycode.toASCII(domain)</a></span></li>
<li><span class="stability_undefined"><a href="#punycode_punycode_tounicode_domain">punycode.toUnicode(domain)</a></span></li>
<li><span class="stability_undefined"><a href="#punycode_punycode_ucs2">punycode.ucs2</a></span><ul>
<li><span class="stability_undefined"><a href="#punycode_punycode_ucs2_decode_string">punycode.ucs2.decode(string)</a></span></li>
<li><span class="stability_undefined"><a href="#punycode_punycode_ucs2_encode_codepoints">punycode.ucs2.encode(codePoints)</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#punycode_punycode_version">punycode.version</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#querystring_query_string">Query String</a></span><ul>
<li><span class="stability_undefined"><a href="#querystring_querystring_escape">querystring.escape</a></span></li>
<li><span class="stability_undefined"><a href="#querystring_querystring_parse_str_sep_eq_options">querystring.parse(str[, sep][, eq][, options])</a></span></li>
<li><span class="stability_undefined"><a href="#querystring_querystring_stringify_obj_sep_eq_options">querystring.stringify(obj[, sep][, eq][, options])</a></span></li>
<li><span class="stability_undefined"><a href="#querystring_querystring_unescape">querystring.unescape</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#readline_readline">Readline</a></span><ul>
<li><span class="stability_undefined"><a href="#readline_class_interface">Class: Interface</a></span><ul>
<li><span class="stability_undefined"><a href="#readline_rl_close">rl.close()</a></span></li>
<li><span class="stability_undefined"><a href="#readline_rl_pause">rl.pause()</a></span></li>
<li><span class="stability_undefined"><a href="#readline_rl_prompt_preservecursor">rl.prompt([preserveCursor])</a></span></li>
<li><span class="stability_undefined"><a href="#readline_rl_question_query_callback">rl.question(query, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#readline_rl_resume">rl.resume()</a></span></li>
<li><span class="stability_undefined"><a href="#readline_rl_setprompt_prompt">rl.setPrompt(prompt)</a></span></li>
<li><span class="stability_undefined"><a href="#readline_rl_write_data_key">rl.write(data[, key])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#readline_events">Events</a></span><ul>
<li><span class="stability_undefined"><a href="#readline_event_close">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#readline_event_line">Event: 'line'</a></span></li>
<li><span class="stability_undefined"><a href="#readline_event_pause">Event: 'pause'</a></span></li>
<li><span class="stability_undefined"><a href="#readline_event_resume">Event: 'resume'</a></span></li>
<li><span class="stability_undefined"><a href="#readline_event_sigcont">Event: 'SIGCONT'</a></span></li>
<li><span class="stability_undefined"><a href="#readline_event_sigint">Event: 'SIGINT'</a></span></li>
<li><span class="stability_undefined"><a href="#readline_event_sigtstp">Event: 'SIGTSTP'</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#readline_example_tiny_cli">Example: Tiny CLI</a></span></li>
<li><span class="stability_undefined"><a href="#readline_example_read_file_stream_line_by_line">Example: Read File Stream Line-by-Line</a></span></li>
<li><span class="stability_undefined"><a href="#readline_readline_clearline_stream_dir">readline.clearLine(stream, dir)</a></span></li>
<li><span class="stability_undefined"><a href="#readline_readline_clearscreendown_stream">readline.clearScreenDown(stream)</a></span></li>
<li><span class="stability_undefined"><a href="#readline_readline_createinterface_options">readline.createInterface(options)</a></span></li>
<li><span class="stability_undefined"><a href="#readline_readline_cursorto_stream_x_y">readline.cursorTo(stream, x, y)</a></span></li>
<li><span class="stability_undefined"><a href="#readline_readline_emitkeypressevents_stream_interface">readline.emitKeypressEvents(stream[, interface])</a></span></li>
<li><span class="stability_undefined"><a href="#readline_readline_movecursor_stream_dx_dy">readline.moveCursor(stream, dx, dy)</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#repl_repl">REPL</a></span><ul>
<li><span class="stability_undefined"><a href="#repl_environment_variable_options">Environment Variable Options</a></span></li>
<li><span class="stability_undefined"><a href="#repl_persistent_history">Persistent History</a></span><ul>
<li><span class="stability_0"><a href="#repl_node_repl_history_file">NODE_REPL_HISTORY_FILE</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#repl_repl_features">REPL Features</a></span><ul>
<li><span class="stability_undefined"><a href="#repl_customizing_object_displays_in_the_repl">Customizing Object displays in the REPL</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#repl_class_replserver">Class: REPLServer</a></span><ul>
<li><span class="stability_undefined"><a href="#repl_event_exit">Event: 'exit'</a></span></li>
<li><span class="stability_undefined"><a href="#repl_event_reset">Event: 'reset'</a></span></li>
<li><span class="stability_undefined"><a href="#repl_replserver_definecommand_keyword_cmd">replServer.defineCommand(keyword, cmd)</a></span></li>
<li><span class="stability_undefined"><a href="#repl_replserver_displayprompt_preservecursor">replServer.displayPrompt([preserveCursor])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#repl_repl_start_options">repl.start(options)</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#stream_stream">Stream</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_api_for_stream_consumers">API for Stream Consumers</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_class_stream_duplex">Class: stream.Duplex</a></span></li>
<li><span class="stability_undefined"><a href="#stream_class_stream_readable">Class: stream.Readable</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_event_close">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_data">Event: 'data'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_end">Event: 'end'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_error">Event: 'error'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_readable">Event: 'readable'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_ispaused">readable.isPaused()</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_pause">readable.pause()</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_pipe_destination_options">readable.pipe(destination[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_read_size">readable.read([size])</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_resume">readable.resume()</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_setencoding_encoding">readable.setEncoding(encoding)</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_unpipe_destination">readable.unpipe([destination])</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_unshift_chunk">readable.unshift(chunk)</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_wrap_stream">readable.wrap(stream)</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#stream_class_stream_transform">Class: stream.Transform</a></span></li>
<li><span class="stability_undefined"><a href="#stream_class_stream_writable">Class: stream.Writable</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_event_close_1">Event: 'close'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_drain">Event: 'drain'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_error_1">Event: 'error'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_finish">Event: 'finish'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_pipe">Event: 'pipe'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_event_unpipe">Event: 'unpipe'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_writable_cork">writable.cork()</a></span></li>
<li><span class="stability_undefined"><a href="#stream_writable_end_chunk_encoding_callback">writable.end([chunk][, encoding][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#stream_writable_setdefaultencoding_encoding">writable.setDefaultEncoding(encoding)</a></span></li>
<li><span class="stability_undefined"><a href="#stream_writable_uncork">writable.uncork()</a></span></li>
<li><span class="stability_undefined"><a href="#stream_writable_write_chunk_encoding_callback">writable.write(chunk[, encoding][, callback])</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#stream_api_for_stream_implementors">API for Stream Implementors</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_class_stream_duplex_1">Class: stream.Duplex</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_new_stream_duplex_options">new stream.Duplex(options)</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#stream_class_stream_passthrough">Class: stream.PassThrough</a></span></li>
<li><span class="stability_undefined"><a href="#stream_class_stream_readable_1">Class: stream.Readable</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_new_stream_readable_options">new stream.Readable([options])</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_read_size_1">readable._read(size)</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable_push_chunk_encoding">readable.push(chunk[, encoding])</a></span></li>
<li><span class="stability_undefined"><a href="#stream_example_a_counting_stream">Example: A Counting Stream</a></span></li>
<li><span class="stability_undefined"><a href="#stream_example_simpleprotocol_v1_sub_optimal">Example: SimpleProtocol v1 (Sub-optimal)</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#stream_class_stream_transform_1">Class: stream.Transform</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_new_stream_transform_options">new stream.Transform([options])</a></span></li>
<li><span class="stability_undefined"><a href="#stream_events_finish_and_end">Events: 'finish' and 'end'</a></span></li>
<li><span class="stability_undefined"><a href="#stream_transform_flush_callback">transform._flush(callback)</a></span></li>
<li><span class="stability_undefined"><a href="#stream_transform_transform_chunk_encoding_callback">transform._transform(chunk, encoding, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#stream_example_simpleprotocol_parser_v2">Example: <code>SimpleProtocol</code> parser v2</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#stream_class_stream_writable_1">Class: stream.Writable</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_new_stream_writable_options">new stream.Writable([options])</a></span></li>
<li><span class="stability_undefined"><a href="#stream_writable_write_chunk_encoding_callback_1">writable._write(chunk, encoding, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#stream_writable_writev_chunks_callback">writable._writev(chunks, callback)</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#stream_simplified_constructor_api">Simplified Constructor API</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_duplex">Duplex</a></span></li>
<li><span class="stability_undefined"><a href="#stream_readable">Readable</a></span></li>
<li><span class="stability_undefined"><a href="#stream_transform">Transform</a></span></li>
<li><span class="stability_undefined"><a href="#stream_writable">Writable</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#stream_streams_under_the_hood">Streams: Under the Hood</a></span><ul>
<li><span class="stability_undefined"><a href="#stream_buffering">Buffering</a></span></li>
<li><span class="stability_undefined"><a href="#stream_compatibility_with_older_node_js_versions">Compatibility with Older Node.js Versions</a></span></li>
<li><span class="stability_undefined"><a href="#stream_object_mode">Object Mode</a></span></li>
<li><span class="stability_undefined"><a href="#stream_stream_read_0"><code>stream.read(0)</code></a></span></li>
<li><span class="stability_undefined"><a href="#stream_stream_push"><code>stream.push('')</code></a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_2"><a href="#string_decoder_string_decoder">String Decoder</a></span><ul>
<li><span class="stability_undefined"><a href="#string_decoder_class_stringdecoder">Class: StringDecoder</a></span><ul>
<li><span class="stability_undefined"><a href="#string_decoder_decoder_end">decoder.end()</a></span></li>
<li><span class="stability_undefined"><a href="#string_decoder_decoder_write_buffer">decoder.write(buffer)</a></span></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_3"><a href="#timers_timers">Timers</a></span><ul>
<li><span class="stability_undefined"><a href="#timers_clearimmediate_immediateobject">clearImmediate(immediateObject)</a></span></li>
<li><span class="stability_undefined"><a href="#timers_clearinterval_intervalobject">clearInterval(intervalObject)</a></span></li>
<li><span class="stability_undefined"><a href="#timers_cleartimeout_timeoutobject">clearTimeout(timeoutObject)</a></span></li>
<li><span class="stability_undefined"><a href="#timers_ref">ref()</a></span></li>
<li><span class="stability_undefined"><a href="#timers_setimmediate_callback_arg">setImmediate(callback[, arg][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#timers_setinterval_callback_delay_arg">setInterval(callback, delay[, arg][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#timers_settimeout_callback_delay_arg">setTimeout(callback, delay[, arg][, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#timers_unref">unref()</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#tls_tls_ssl">TLS (SSL)</a></span><ul>
<li><span class="stability_undefined"><a href="#tls_client_initiated_renegotiation_attack_mitigation">Client-initiated renegotiation attack mitigation</a></span></li>
<li><span class="stability_undefined"><a href="#tls_modifying_the_default_tls_cipher_suite">Modifying the Default TLS Cipher suite</a></span></li>
<li><span class="stability_undefined"><a href="#tls_alpn_npn_and_sni">ALPN, NPN and SNI</a></span></li>
<li><span class="stability_undefined"><a href="#tls_perfect_forward_secrecy">Perfect Forward Secrecy</a></span></li>
<li><span class="stability_0"><a href="#tls_class_cryptostream">Class: CryptoStream</a></span><ul>
<li><span class="stability_undefined"><a href="#tls_cryptostream_byteswritten">cryptoStream.bytesWritten</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#tls_class_securepair">Class: SecurePair</a></span><ul>
<li><span class="stability_undefined"><a href="#tls_event_secure">Event: 'secure'</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#tls_class_tls_server">Class: tls.Server</a></span><ul>
<li><span class="stability_undefined"><a href="#tls_event_clienterror">Event: 'clientError'</a></span></li>
<li><span class="stability_undefined"><a href="#tls_event_newsession">Event: 'newSession'</a></span></li>
<li><span class="stability_undefined"><a href="#tls_event_ocsprequest">Event: 'OCSPRequest'</a></span></li>
<li><span class="stability_undefined"><a href="#tls_event_resumesession">Event: 'resumeSession'</a></span></li>
<li><span class="stability_undefined"><a href="#tls_event_secureconnection">Event: 'secureConnection'</a></span></li>
<li><span class="stability_undefined"><a href="#tls_server_addcontext_hostname_context">server.addContext(hostname, context)</a></span></li>
<li><span class="stability_undefined"><a href="#tls_server_address">server.address()</a></span></li>
<li><span class="stability_undefined"><a href="#tls_server_close_callback">server.close([callback])</a></span></li>
<li><span class="stability_undefined"><a href="#tls_server_connections">server.connections</a></span></li>
<li><span class="stability_undefined"><a href="#tls_server_getticketkeys">server.getTicketKeys()</a></span></li>
<li><span class="stability_undefined"><a href="#tls_server_listen_port_hostname_callback">server.listen(port[, hostname][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#tls_server_maxconnections">server.maxConnections</a></span></li>
<li><span class="stability_undefined"><a href="#tls_server_setticketkeys_keys">server.setTicketKeys(keys)</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#tls_class_tls_tlssocket">Class: tls.TLSSocket</a></span></li>
<li><span class="stability_undefined"><a href="#tls_new_tls_tlssocket_socket_options">new tls.TLSSocket(socket[, options])</a></span><ul>
<li><span class="stability_undefined"><a href="#tls_event_ocspresponse">Event: 'OCSPResponse'</a></span></li>
<li><span class="stability_undefined"><a href="#tls_event_secureconnect">Event: 'secureConnect'</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_address">tlsSocket.address()</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_authorized">tlsSocket.authorized</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_authorizationerror">tlsSocket.authorizationError</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_encrypted">tlsSocket.encrypted</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_getcipher">tlsSocket.getCipher()</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_getpeercertificate_detailed">tlsSocket.getPeerCertificate([ detailed ])</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_getsession">tlsSocket.getSession()</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_gettlsticket">tlsSocket.getTLSTicket()</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_localport">tlsSocket.localPort</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_localaddress">tlsSocket.localAddress</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_remoteaddress">tlsSocket.remoteAddress</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_remotefamily">tlsSocket.remoteFamily</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_remoteport">tlsSocket.remotePort</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_renegotiate_options_callback">tlsSocket.renegotiate(options, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tlssocket_setmaxsendfragment_size">tlsSocket.setMaxSendFragment(size)</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#tls_tls_connect_options_callback">tls.connect(options[, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tls_connect_port_host_options_callback">tls.connect(port[, host][, options][, callback])</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tls_createsecurecontext_details">tls.createSecureContext(details)</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tls_createsecurepair_context_isserver_requestcert_rejectunauthorized_options">tls.createSecurePair([context][, isServer][, requestCert][, rejectUnauthorized][, options])</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tls_createserver_options_secureconnectionlistener">tls.createServer(options[, secureConnectionListener])</a></span></li>
<li><span class="stability_undefined"><a href="#tls_tls_getciphers">tls.getCiphers()</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#tty_tty">TTY</a></span><ul>
<li><span class="stability_undefined"><a href="#tty_class_readstream">Class: ReadStream</a></span><ul>
<li><span class="stability_undefined"><a href="#tty_rs_israw">rs.isRaw</a></span></li>
<li><span class="stability_undefined"><a href="#tty_rs_setrawmode_mode">rs.setRawMode(mode)</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#tty_class_writestream">Class: WriteStream</a></span><ul>
<li><span class="stability_undefined"><a href="#tty_event_resize">Event: 'resize'</a></span></li>
<li><span class="stability_undefined"><a href="#tty_ws_columns">ws.columns</a></span></li>
<li><span class="stability_undefined"><a href="#tty_ws_rows">ws.rows</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#tty_tty_isatty_fd">tty.isatty(fd)</a></span></li>
<li><span class="stability_0"><a href="#tty_tty_setrawmode_mode">tty.setRawMode(mode)</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#url_url">URL</a></span><ul>
<li><span class="stability_undefined"><a href="#url_url_parsing">URL Parsing</a></span><ul>
<li><span class="stability_undefined"><a href="#url_escaped_characters">Escaped Characters</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#url_url_format_urlobj">url.format(urlObj)</a></span></li>
<li><span class="stability_undefined"><a href="#url_url_parse_urlstr_parsequerystring_slashesdenotehost">url.parse(urlStr[, parseQueryString][, slashesDenoteHost])</a></span></li>
<li><span class="stability_undefined"><a href="#url_url_resolve_from_to">url.resolve(from, to)</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#util_util">Util</a></span><ul>
<li><span class="stability_0"><a href="#util_util_debug_string">util.debug(string)</a></span></li>
<li><span class="stability_undefined"><a href="#util_util_debuglog_section">util.debuglog(section)</a></span></li>
<li><span class="stability_undefined"><a href="#util_util_deprecate_function_string">util.deprecate(function, string)</a></span></li>
<li><span class="stability_0"><a href="#util_util_error">util.error([...])</a></span></li>
<li><span class="stability_undefined"><a href="#util_util_format_format">util.format(format[, ...])</a></span></li>
<li><span class="stability_undefined"><a href="#util_util_inherits_constructor_superconstructor">util.inherits(constructor, superConstructor)</a></span></li>
<li><span class="stability_undefined"><a href="#util_util_inspect_object_options">util.inspect(object[, options])</a></span><ul>
<li><span class="stability_undefined"><a href="#util_customizing_util_inspect_colors">Customizing <code>util.inspect</code> colors</a></span></li>
<li><span class="stability_undefined"><a href="#util_custom_inspect_function_on_objects">Custom <code>inspect()</code> function on Objects</a></span></li>
</ul>
</li>
<li><span class="stability_0"><a href="#util_util_isarray_object">util.isArray(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isboolean_object">util.isBoolean(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isbuffer_object">util.isBuffer(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isdate_object">util.isDate(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_iserror_object">util.isError(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isfunction_object">util.isFunction(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isnull_object">util.isNull(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isnullorundefined_object">util.isNullOrUndefined(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isnumber_object">util.isNumber(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isobject_object">util.isObject(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isprimitive_object">util.isPrimitive(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isregexp_object">util.isRegExp(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isstring_object">util.isString(object)</a></span><ul>
<li><span class="stability_0"><a href="#util_util_issymbol_object">util.isSymbol(object)</a></span></li>
</ul>
</li>
<li><span class="stability_0"><a href="#util_util_isundefined_object">util.isUndefined(object)</a></span></li>
<li><span class="stability_undefined"><a href="#util_util_log_string">util.log(string)</a></span></li>
<li><span class="stability_0"><a href="#util_util_print">util.print([...])</a></span></li>
<li><span class="stability_0"><a href="#util_util_pump_readablestream_writablestream_callback">util.pump(readableStream, writableStream[, callback])</a></span></li>
<li><span class="stability_0"><a href="#util_util_puts">util.puts([...])</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#v8_v8">V8</a></span><ul>
<li><span class="stability_undefined"><a href="#v8_getheapstatistics">getHeapStatistics()</a></span></li>
<li><span class="stability_undefined"><a href="#v8_getheapspacestatistics">getHeapSpaceStatistics()</a></span></li>
<li><span class="stability_undefined"><a href="#v8_setflagsfromstring_string">setFlagsFromString(string)</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#vm_vm_executing_javascript">VM (Executing JavaScript)</a></span><ul>
<li><span class="stability_undefined"><a href="#vm_class_script">Class: Script</a></span><ul>
<li><span class="stability_undefined"><a href="#vm_new_vm_script_code_options">new vm.Script(code, options)</a></span></li>
<li><span class="stability_undefined"><a href="#vm_script_runincontext_contextifiedsandbox_options">script.runInContext(contextifiedSandbox[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#vm_script_runinnewcontext_sandbox_options">script.runInNewContext([sandbox][, options])</a></span></li>
<li><span class="stability_undefined"><a href="#vm_script_runinthiscontext_options">script.runInThisContext([options])</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#vm_vm_createcontext_sandbox">vm.createContext([sandbox])</a></span></li>
<li><span class="stability_undefined"><a href="#vm_vm_iscontext_sandbox">vm.isContext(sandbox)</a></span></li>
<li><span class="stability_undefined"><a href="#vm_vm_runincontext_code_contextifiedsandbox_options">vm.runInContext(code, contextifiedSandbox[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#vm_vm_runindebugcontext_code">vm.runInDebugContext(code)</a></span></li>
<li><span class="stability_undefined"><a href="#vm_vm_runinnewcontext_code_sandbox_options">vm.runInNewContext(code[, sandbox][, options])</a></span></li>
<li><span class="stability_undefined"><a href="#vm_vm_runinthiscontext_code_options">vm.runInThisContext(code[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#vm_example_run_a_server_within_a_vm">Example: Run a Server within a VM</a></span></li>
</ul>
</li>
<li><span class="stability_2"><a href="#zlib_zlib">Zlib</a></span><ul>
<li><span class="stability_undefined"><a href="#zlib_examples">Examples</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_memory_usage_tuning">Memory Usage Tuning</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_flushing">Flushing</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_constants">Constants</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_options">Class Options</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_zlib_deflate">Class: zlib.Deflate</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_zlib_deflateraw">Class: zlib.DeflateRaw</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_zlib_gunzip">Class: zlib.Gunzip</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_zlib_gzip">Class: zlib.Gzip</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_zlib_inflate">Class: zlib.Inflate</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_zlib_inflateraw">Class: zlib.InflateRaw</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_zlib_unzip">Class: zlib.Unzip</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_class_zlib_zlib">Class: zlib.Zlib</a></span><ul>
<li><span class="stability_undefined"><a href="#zlib_zlib_flush_kind_callback">zlib.flush([kind], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_params_level_strategy_callback">zlib.params(level, strategy, callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_reset">zlib.reset()</a></span></li>
</ul>
</li>
<li><span class="stability_undefined"><a href="#zlib_zlib_createdeflate_options">zlib.createDeflate([options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_createdeflateraw_options">zlib.createDeflateRaw([options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_creategunzip_options">zlib.createGunzip([options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_creategzip_options">zlib.createGzip([options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_createinflate_options">zlib.createInflate([options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_createinflateraw_options">zlib.createInflateRaw([options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_createunzip_options">zlib.createUnzip([options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_convenience_methods">Convenience Methods</a></span><ul>
<li><span class="stability_undefined"><a href="#zlib_zlib_deflate_buf_options_callback">zlib.deflate(buf[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_deflatesync_buf_options">zlib.deflateSync(buf[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_deflateraw_buf_options_callback">zlib.deflateRaw(buf[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_deflaterawsync_buf_options">zlib.deflateRawSync(buf[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_gunzip_buf_options_callback">zlib.gunzip(buf[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_gunzipsync_buf_options">zlib.gunzipSync(buf[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_gzip_buf_options_callback">zlib.gzip(buf[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_gzipsync_buf_options">zlib.gzipSync(buf[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_inflate_buf_options_callback">zlib.inflate(buf[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_inflatesync_buf_options">zlib.inflateSync(buf[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_inflateraw_buf_options_callback">zlib.inflateRaw(buf[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_inflaterawsync_buf_options">zlib.inflateRawSync(buf[, options])</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_unzip_buf_options_callback">zlib.unzip(buf[, options], callback)</a></span></li>
<li><span class="stability_undefined"><a href="#zlib_zlib_unzipsync_buf_options">zlib.unzipSync(buf[, options])</a></span></li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<div id="apicontent">
<!-- [start-include:documentation.md] -->
<h1>About this Documentation<span><a class="mark" href="#documentation_about_this_documentation" id="documentation_about_this_documentation">#</a></span></h1>
<!-- type=misc -->
<p>The goal of this documentation is to comprehensively explain the Node.js
API, both from a reference as well as a conceptual point of view. Each
section describes a built-in module or high-level concept.</p>
<p>Where appropriate, property types, method arguments, and the arguments
provided to event handlers are detailed in a list underneath the topic
heading.</p>
<p>Every <code>.html</code> document has a corresponding <code>.json</code> document presenting
the same information in a structured manner. This feature is
experimental, and added for the benefit of IDEs and other utilities that
wish to do programmatic things with the documentation.</p>
<p>Every <code>.html</code> and <code>.json</code> file is generated based on the corresponding
<code>.md</code> file in the <code>doc/api/</code> folder in Node.js's source tree. The
documentation is generated using the <code>tools/doc/generate.js</code> program.
The HTML template is located at <code>doc/template.html</code>.</p>
<p>If you find an error in this documentation, please <a href="https://github.com/nodejs/node/issues/new">submit an issue</a>
or see <a href="https://github.com/nodejs/node/blob/master/CONTRIBUTING.md">the contributing guide</a> for directions on how to submit a patch.</p>
<h2>Stability Index<span><a class="mark" href="#documentation_stability_index" id="documentation_stability_index">#</a></span></h2>
<!--type=misc-->
<p>Throughout the documentation, you will see indications of a section's
stability. The Node.js API is still somewhat changing, and as it
matures, certain parts are more reliable than others. Some are so
proven, and so relied upon, that they are unlikely to ever change at
all. Others are brand new and experimental, or known to be hazardous
and in the process of being redesigned.</p>
<p>The stability indices are as follows:</p>
<pre class="api_stability api_stability_0">Stability: 0 - Deprecated This feature is known to be problematic, and changes are planned. Do not rely on it. Use of the feature may cause warnings. Backwards compatibility should not be expected.</pre><pre class="api_stability api_stability_1">Stability: 1 - Experimental This feature is subject to change, and is gated by a command line flag. It may change or be removed in future versions.</pre><pre class="api_stability api_stability_2">Stability: 2 - Stable The API has proven satisfactory. Compatibility with the npm ecosystem is a high priority, and will not be broken unless absolutely necessary.</pre><pre class="api_stability api_stability_3">Stability: 3 - Locked Only bug fixes, security fixes, and performance improvements will be accepted. Please do not suggest API changes in this area; they will be refused.</pre><h2>JSON Output<span><a class="mark" href="#documentation_json_output" id="documentation_json_output">#</a></span></h2>
<pre class="api_stability api_stability_1">Stability: 1 - Experimental</pre><p>Every HTML file in the markdown has a corresponding JSON file with the
same data.</p>
<p>This feature was added in Node.js v0.6.12. It is experimental.</p>
<h2>Syscalls and man pages<span><a class="mark" href="#documentation_syscalls_and_man_pages" id="documentation_syscalls_and_man_pages">#</a></span></h2>
<p>System calls like <a href="http://man7.org/linux/man-pages/man2/open.2.html">open(2)</a> and <a href="http://man7.org/linux/man-pages/man2/read.2.html">read(2)</a> define the interface between user programs
and the underlying operating system. Node functions which simply wrap a syscall,
like <code>fs.open()</code>, will document that. The docs link to the corresponding man
pages (short for manual pages) which describe how the syscalls work.</p>
<p><strong>Caveat:</strong> some syscalls, like <a href="http://man7.org/linux/man-pages/man2/lchown.2.html">lchown(2)</a>, are BSD-specific. That means, for
example, that <code>fs.lchown()</code> only works on Mac OS X and other BSD-derived systems,
and is not available on Linux.</p>
<p>Most Unix syscalls have Windows equivalents, but behavior may differ on Windows
relative to Linux and OS X. For an example of the subtle ways in which it's
sometimes impossible to replace Unix syscall semantics on Windows, see <a href="https://github.com/nodejs/node/issues/4760">Node
issue 4760</a>.</p>
<!-- [end-include:documentation.md] -->
<!-- [start-include:synopsis.md] -->
<h1>Usage<span><a class="mark" href="#synopsis_usage" id="synopsis_usage">#</a></span></h1>
<!--type=misc-->
<p><code>node [options] [v8 options] [script.js | -e "script"] [arguments]</code></p>
<p>Please see the <a href="cli.html#cli_command_line_options">Command Line Options</a> document for information about
different options and ways to run scripts with Node.</p>
<h2>Example<span><a class="mark" href="#synopsis_example" id="synopsis_example">#</a></span></h2>
<p>An example of a <a href="http.html">web server</a> written with Node.js which responds with
<code>'Hello World'</code>:</p>
<pre><code class="lang-js">const http = require('http');
const hostname = '127.0.0.1';
const port = 3000;
const server = http.createServer((req, res) => {
res.statusCode = 200;
res.setHeader('Content-Type', 'text/plain');
res.end('Hello World\n');
});
server.listen(port, hostname, () => {
console.log(`Server running at http://${hostname}:${port}/`);
});
</code></pre>
<p>To run the server, put the code into a file called <code>example.js</code> and execute
it with Node.js:</p>
<pre><code>$ node example.js
Server running at http://127.0.0.1:3000/
</code></pre><p>All of the examples in the documentation can be run similarly.</p>
<!-- [end-include:synopsis.md] -->
<!-- [start-include:addons.md] -->
<h1>C/C++ Addons<span><a class="mark" href="#addons_c_c_addons" id="addons_c_c_addons">#</a></span></h1>
<p>Node.js Addons are dynamically-linked shared objects, written in C or C++, that
can be loaded into Node.js using the <a href="globals.html#globals_require"><code>require()</code></a> function, and used
just as if they were an ordinary Node.js module. They are used primarily to
provide an interface between JavaScript running in Node.js and C/C++ libraries.</p>
<p>At the moment, the method for implementing Addons is rather complicated,
involving knowledge of several components and APIs :</p>
<ul>
<li><p>V8: the C++ library Node.js currently uses to provide the
JavaScript implementation. V8 provides the mechanisms for creating objects,
calling functions, etc. V8's API is documented mostly in the
<code>v8.h</code> header file (<code>deps/v8/include/v8.h</code> in the Node.js source
tree), which is also available <a href="https://v8docs.nodesource.com/">online</a>.</p>
</li>
<li><p><a href="https://github.com/libuv/libuv">libuv</a>: The C library that implements the Node.js event loop, its worker
threads and all of the asynchronous behaviors of the platform. It also
serves as a cross-platform abstraction library, giving easy, POSIX-like
access across all major operating systems to many common system tasks, such
as interacting with the filesystem, sockets, timers and system events. libuv
also provides a pthreads-like threading abstraction that may be used to
power more sophisticated asynchronous Addons that need to move beyond the
standard event loop. Addon authors are encouraged to think about how to
avoid blocking the event loop with I/O or other time-intensive tasks by
off-loading work via libuv to non-blocking system operations, worker threads
or a custom use of libuv's threads.</p>
</li>
<li><p>Internal Node.js libraries. Node.js itself exports a number of C/C++ APIs
that Addons can use — the most important of which is the
<code>node::ObjectWrap</code> class.</p>
</li>
<li><p>Node.js includes a number of other statically linked libraries including
OpenSSL. These other libraries are located in the <code>deps/</code> directory in the
Node.js source tree. Only the V8 and OpenSSL symbols are purposefully
re-exported by Node.js and may be used to various extents by Addons.
See <a href="#linking-to-nodejs-own-dependencies">Linking to Node.js' own dependencies</a> for additional information.</p>
</li>
</ul>
<p>All of the following examples are available for <a href="https://github.com/nodejs/node-addon-examples">download</a> and may
be used as a starting-point for your own Addon.</p>
<h2>Hello world<span><a class="mark" href="#addons_hello_world" id="addons_hello_world">#</a></span></h2>
<p>This "Hello world" example is a simple Addon, written in C++, that is the
equivalent of the following JavaScript code:</p>
<pre><code class="lang-js">module.exports.hello = () => 'world';
</code></pre>
<p>First, create the file <code>hello.cc</code>:</p>
<pre><code class="lang-cpp">// hello.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
}
void init(Local<Object> exports) {
NODE_SET_METHOD(exports, "hello", Method);
}
NODE_MODULE(addon, init)
} // namespace demo
</code></pre>
<p>Note that all Node.js Addons must export an initialization function following
the pattern:</p>
<pre><code class="lang-cpp">void Initialize(Local<Object> exports);
NODE_MODULE(module_name, Initialize)
</code></pre>
<p>There is no semi-colon after <code>NODE_MODULE</code> as it's not a function (see
<code>node.h</code>).</p>
<p>The <code>module_name</code> must match the filename of the final binary (excluding
the .node suffix).</p>
<p>In the <code>hello.cc</code> example, then, the initialization function is <code>init</code> and the
Addon module name is <code>addon</code>.</p>
<h3>Building<span><a class="mark" href="#addons_building" id="addons_building">#</a></span></h3>
<p>Once the source code has been written, it must be compiled into the binary
<code>addon.node</code> file. To do so, create a file called <code>binding.gyp</code> in the
top-level of the project describing the build configuration of your module
using a JSON-like format. This file is used by <a href="https://github.com/nodejs/node-gyp">node-gyp</a> -- a tool written
specifically to compile Node.js Addons.</p>
<pre><code>{
"targets": [
{
"target_name": "addon",
"sources": [ "hello.cc" ]
}
]
}
</code></pre><p><em>Note: A version of the <code>node-gyp</code> utility is bundled and distributed with
Node.js as part of <code>npm</code>. This version is not made directly available for
developers to use and is intended only to support the ability to use the
<code>npm install</code> command to compile and install Addons. Developers who wish to
use <code>node-gyp</code> directly can install it using the command
<code>npm install -g node-gyp</code>. See the <code>node-gyp</code> <a href="https://github.com/nodejs/node-gyp#installation">installation instructions</a> for
more information, including platform-specific requirements.</em></p>
<p>Once the <code>binding.gyp</code> file has been created, use <code>node-gyp configure</code> to
generate the appropriate project build files for the current platform. This
will generate either a <code>Makefile</code> (on Unix platforms) or a <code>vcxproj</code> file
(on Windows) in the <code>build/</code> directory.</p>
<p>Next, invoke the <code>node-gyp build</code> command to generate the compiled <code>addon.node</code>
file. This will be put into the <code>build/Release/</code> directory.</p>
<p>When using <code>npm install</code> to install a Node.js Addon, npm uses its own bundled
version of <code>node-gyp</code> to perform this same set of actions, generating a
compiled version of the Addon for the user's platform on demand.</p>
<p>Once built, the binary Addon can be used from within Node.js by pointing
<a href="globals.html#globals_require"><code>require()</code></a> to the built <code>addon.node</code> module:</p>
<pre><code class="lang-js">// hello.js
const addon = require('./build/Release/addon');
console.log(addon.hello()); // 'world'
</code></pre>
<p>Please see the examples below for further information or
<a href="https://github.com/arturadib/node-qt">https://github.com/arturadib/node-qt</a> for an example in production.</p>
<p>Because the exact path to the compiled Addon binary can vary depending on how
it is compiled (i.e. sometimes it may be in <code>./build/Debug/</code>), Addons can use
the <a href="https://github.com/TooTallNate/node-bindings">bindings</a> package to load the compiled module.</p>
<p>Note that while the <code>bindings</code> package implementation is more sophisticated
in how it locates Addon modules, it is essentially using a try-catch pattern
similar to:</p>
<pre><code class="lang-js">try {
return require('./build/Release/addon.node');
} catch (err) {
return require('./build/Debug/addon.node');
}
</code></pre>
<h3>Linking to Node.js' own dependencies<span><a class="mark" href="#addons_linking_to_node_js_own_dependencies" id="addons_linking_to_node_js_own_dependencies">#</a></span></h3>
<p>Node.js uses a number of statically linked libraries such as V8, libuv and
OpenSSL. All Addons are required to link to V8 and may link to any of the
other dependencies as well. Typically, this is as simple as including
the appropriate <code>#include <...></code> statements (e.g. <code>#include <v8.h></code>) and
<code>node-gyp</code> will locate the appropriate headers automatically. However, there
are a few caveats to be aware of:</p>
<ul>
<li><p>When <code>node-gyp</code> runs, it will detect the specific release version of Node.js
and download either the full source tarball or just the headers. If the full
source is downloaded, Addons will have complete access to the full set of
Node.js dependencies. However, if only the Node.js headers are downloaded, then
only the symbols exported by Node.js will be available.</p>
</li>
<li><p><code>node-gyp</code> can be run using the <code>--nodedir</code> flag pointing at a local Node.js
source image. Using this option, the Addon will have access to the full set of
dependencies.</p>
</li>
</ul>
<h3>Loading Addons using require()<span><a class="mark" href="#addons_loading_addons_using_require" id="addons_loading_addons_using_require">#</a></span></h3>
<p>The filename extension of the compiled Addon binary is <code>.node</code> (as opposed
to <code>.dll</code> or <code>.so</code>). The <a href="globals.html#globals_require"><code>require()</code></a> function is written to look for
files with the <code>.node</code> file extension and initialize those as dynamically-linked
libraries.</p>
<p>When calling <a href="globals.html#globals_require"><code>require()</code></a>, the <code>.node</code> extension can usually be
omitted and Node.js will still find and initialize the Addon. One caveat,
however, is that Node.js will first attempt to locate and load modules or
JavaScript files that happen to share the same base name. For instance, if
there is a file <code>addon.js</code> in the same directory as the binary <code>addon.node</code>,
then <a href="globals.html#globals_require"><code>require('addon')</code></a> will give precedence to the <code>addon.js</code> file
and load it instead.</p>
<h2>Native Abstractions for Node.js<span><a class="mark" href="#addons_native_abstractions_for_node_js" id="addons_native_abstractions_for_node_js">#</a></span></h2>
<p>Each of the examples illustrated in this document make direct use of the
Node.js and V8 APIs for implementing Addons. It is important to understand
that the V8 API can, and has, changed dramatically from one V8 release to the
next (and one major Node.js release to the next). With each change, Addons may
need to be updated and recompiled in order to continue functioning. The Node.js
release schedule is designed to minimize the frequency and impact of such
changes but there is little that Node.js can do currently to ensure stability
of the V8 APIs.</p>
<p>The <a href="https://github.com/nodejs/nan">Native Abstractions for Node.js</a> (or <code>nan</code>) provide a set of tools that
Addon developers are recommended to use to keep compatibility between past and
future releases of V8 and Node.js. See the <code>nan</code> <a href="https://github.com/nodejs/nan/tree/master/examples/">examples</a> for an
illustration of how it can be used.</p>
<h2>Addon examples<span><a class="mark" href="#addons_addon_examples" id="addons_addon_examples">#</a></span></h2>
<p>Following are some example Addons intended to help developers get started. The
examples make use of the V8 APIs. Refer to the online <a href="https://v8docs.nodesource.com/">V8 reference</a>
for help with the various V8 calls, and V8's <a href="https://developers.google.com/v8/embed">Embedder's Guide</a> for an
explanation of several concepts used such as handles, scopes, function
templates, etc.</p>
<p>Each of these examples using the following <code>binding.gyp</code> file:</p>
<pre><code>{
"targets": [
{
"target_name": "addon",
"sources": [ "addon.cc" ]
}
]
}
</code></pre><p>In cases where there is more than one <code>.cc</code> file, simply add the additional
filename to the <code>sources</code> array. For example:</p>
<pre><code>"sources": ["addon.cc", "myexample.cc"]
</code></pre><p>Once the <code>binding.gyp</code> file is ready, the example Addons can be configured and
built using <code>node-gyp</code>:</p>
<pre><code>$ node-gyp configure build
</code></pre><h3>Function arguments<span><a class="mark" href="#addons_function_arguments" id="addons_function_arguments">#</a></span></h3>
<p>Addons will typically expose objects and functions that can be accessed from
JavaScript running within Node.js. When functions are invoked from JavaScript,
the input arguments and return value must be mapped to and from the C/C++
code.</p>
<p>The following example illustrates how to read function arguments passed from
JavaScript and how to return a result:</p>
<pre><code class="lang-cpp">// addon.cc
#include <node.h>
namespace demo {
using v8::Exception;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
// This is the implementation of the "add" method
// Input arguments are passed using the
// const FunctionCallbackInfo<Value>& args struct
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
// Check the number of arguments passed.
if (args.Length() < 2) {
// Throw an Error that is passed back to JavaScript
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong number of arguments")));
return;
}
// Check the argument types
if (!args[0]->IsNumber() || !args[1]->IsNumber()) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong arguments")));
return;
}
// Perform the operation
double value = args[0]->NumberValue() + args[1]->NumberValue();
Local<Number> num = Number::New(isolate, value);
// Set the return value (using the passed in
// FunctionCallbackInfo<Value>&)
args.GetReturnValue().Set(num);
}
void Init(Local<Object> exports) {
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, Init)
} // namespace demo
</code></pre>
<p>Once compiled, the example Addon can be required and used from within Node.js:</p>
<pre><code class="lang-js">// test.js
const addon = require('./build/Release/addon');
console.log('This should be eight:', addon.add(3, 5));
</code></pre>
<h3>Callbacks<span><a class="mark" href="#addons_callbacks" id="addons_callbacks">#</a></span></h3>
<p>It is common practice within Addons to pass JavaScript functions to a C++
function and execute them from there. The following example illustrates how
to invoke such callbacks:</p>
<pre><code class="lang-cpp">// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = { String::NewFromUtf8(isolate, "hello world") };
cb->Call(Null(isolate), argc, argv);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(addon, Init)
} // namespace demo
</code></pre>
<p>Note that this example uses a two-argument form of <code>Init()</code> that receives
the full <code>module</code> object as the second argument. This allows the Addon
to completely overwrite <code>exports</code> with a single function instead of
adding the function as a property of <code>exports</code>.</p>
<p>To test it, run the following JavaScript:</p>
<pre><code class="lang-js">// test.js
const addon = require('./build/Release/addon');
addon((msg) => {
console.log(msg); // 'hello world'
});
</code></pre>
<p>Note that, in this example, the callback function is invoked synchronously.</p>
<h3>Object factory<span><a class="mark" href="#addons_object_factory" id="addons_object_factory">#</a></span></h3>
<p>Addons can create and return new objects from within a C++ function as
illustrated in the following example. An object is created and returned with a
property <code>msg</code> that echoes the string passed to <code>createObject()</code>:</p>
<pre><code class="lang-cpp">// addon.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Object> obj = Object::New(isolate);
obj->Set(String::NewFromUtf8(isolate, "msg"), args[0]->ToString());
args.GetReturnValue().Set(obj);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, Init)
} // namespace demo
</code></pre>
<p>To test it in JavaScript:</p>
<pre><code class="lang-js">// test.js
const addon = require('./build/Release/addon');
var obj1 = addon('hello');
var obj2 = addon('world');
console.log(obj1.msg, obj2.msg); // 'hello world'
</code></pre>
<h3>Function factory<span><a class="mark" href="#addons_function_factory" id="addons_function_factory">#</a></span></h3>
<p>Another common scenario is creating JavaScript functions that wrap C++
functions and returning those back to JavaScript:</p>
<pre><code class="lang-cpp">// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void MyFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world"));
}
void CreateFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, MyFunction);
Local<Function> fn = tpl->GetFunction();
// omit this to make it anonymous
fn->SetName(String::NewFromUtf8(isolate, "theFunction"));
args.GetReturnValue().Set(fn);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateFunction);
}
NODE_MODULE(addon, Init)
} // namespace demo
</code></pre>
<p>To test:</p>
<pre><code class="lang-js">// test.js
const addon = require('./build/Release/addon');
var fn = addon();
console.log(fn()); // 'hello world'
</code></pre>
<h3>Wrapping C++ objects<span><a class="mark" href="#addons_wrapping_c_objects" id="addons_wrapping_c_objects">#</a></span></h3>
<p>It is also possible to wrap C++ objects/classes in a way that allows new
instances to be created using the JavaScript <code>new</code> operator:</p>
<pre><code class="lang-cpp">// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Local;
using v8::Object;
void InitAll(Local<Object> exports) {
MyObject::Init(exports);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
</code></pre>
<p>Then, in <code>myobject.h</code>, the wrapper class inherits from <code>node::ObjectWrap</code>:</p>
<pre><code class="lang-cpp">// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Local<v8::Object> exports);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
</code></pre>
<p>In <code>myobject.cc</code>, implement the various methods that are to be exposed.
Below, the method <code>plusOne()</code> is exposed by adding it to the constructor's
prototype:</p>
<pre><code class="lang-cpp">// myobject.cc
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Local<Object> exports) {
Isolate* isolate = exports->GetIsolate();
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
exports->Set(String::NewFromUtf8(isolate, "MyObject"),
tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> result =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(result);
}
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
</code></pre>
<p>To build this example, the <code>myobject.cc</code> file must be added to the
<code>binding.gyp</code>:</p>
<pre><code>{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
</code></pre><p>Test it with:</p>
<pre><code class="lang-js">// test.js
const addon = require('./build/Release/addon');
var obj = new addon.MyObject(10);
console.log(obj.plusOne()); // 11
console.log(obj.plusOne()); // 12
console.log(obj.plusOne()); // 13
</code></pre>
<h3>Factory of wrapped objects<span><a class="mark" href="#addons_factory_of_wrapped_objects" id="addons_factory_of_wrapped_objects">#</a></span></h3>
<p>Alternatively, it is possible to use a factory pattern to avoid explicitly
creating object instances using the JavaScript <code>new</code> operator:</p>
<pre><code class="lang-js">var obj = addon.createObject();
// instead of:
// var obj = new addon.Object();
</code></pre>
<p>First, the <code>createObject()</code> method is implemented in <code>addon.cc</code>:</p>
<pre><code class="lang-cpp">// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void InitAll(Local<Object> exports, Local<Object> module) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
</code></pre>
<p>In <code>myobject.h</code>, the static method <code>NewInstance()</code> is added to handle
instantiating the object. This method takes the place of using <code>new</code> in
JavaScript:</p>
<pre><code class="lang-cpp">// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
</code></pre>
<p>The implementation in <code>myobject.cc</code> is similar to the previous example:</p>
<pre><code class="lang-cpp">// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
</code></pre>
<p>Once again, to build this example, the <code>myobject.cc</code> file must be added to the
<code>binding.gyp</code>:</p>
<pre><code>{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
</code></pre><p>Test it with:</p>
<pre><code class="lang-js">// test.js
const createObject = require('./build/Release/addon');
var obj = createObject(10);
console.log(obj.plusOne()); // 11
console.log(obj.plusOne()); // 12
console.log(obj.plusOne()); // 13
var obj2 = createObject(20);
console.log(obj2.plusOne()); // 21
console.log(obj2.plusOne()); // 22
console.log(obj2.plusOne()); // 23
</code></pre>
<h3>Passing wrapped objects around<span><a class="mark" href="#addons_passing_wrapped_objects_around" id="addons_passing_wrapped_objects_around">#</a></span></h3>
<p>In addition to wrapping and returning C++ objects, it is possible to pass
wrapped objects around by unwrapping them with the Node.js helper function
<code>node::ObjectWrap::Unwrap</code>. The following examples shows a function <code>add()</code>
that can take two <code>MyObject</code> objects as input arguments:</p>
<pre><code class="lang-cpp">// addon.cc
#include <node.h>
#include <node_object_wrap.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(
args[0]->ToObject());
MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(
args[1]->ToObject());
double sum = obj1->value() + obj2->value();
args.GetReturnValue().Set(Number::New(isolate, sum));
}
void InitAll(Local<Object> exports) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(exports, "createObject", CreateObject);
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
</code></pre>
<p>In <code>myobject.h</code>, a new public method is added to allow access to private values
after unwrapping the object.</p>
<pre><code class="lang-cpp">// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
inline double value() const { return value_; }
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
</code></pre>
<p>The implementation of <code>myobject.cc</code> is similar to before:</p>
<pre><code class="lang-cpp">// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
} // namespace demo
</code></pre>
<p>Test it with:</p>
<pre><code class="lang-js">// test.js
const addon = require('./build/Release/addon');
var obj1 = addon.createObject(10);
var obj2 = addon.createObject(20);
var result = addon.add(obj1, obj2);
console.log(result); // 30
</code></pre>
<h3>AtExit hooks<span><a class="mark" href="#addons_atexit_hooks" id="addons_atexit_hooks">#</a></span></h3>
<p>An "AtExit" hook is a function that is invoked after the Node.js event loop
has ended but before the JavaScript VM is terminated and Node.js shuts down.
"AtExit" hooks are registered using the <code>node::AtExit</code> API.</p>
<h4>void AtExit(callback, args)<span><a class="mark" href="#addons_void_atexit_callback_args" id="addons_void_atexit_callback_args">#</a></span></h4>
<div class="signature"><ul>
<li><code>callback</code>: <code>void (*)(void*)</code> - A pointer to the function to call at exit.</li>
<li><code>args</code>: <code>void*</code> - A pointer to pass to the callback at exit.</li>
</ul>
</div><p>Registers exit hooks that run after the event loop has ended but before the VM
is killed.</p>
<p>AtExit takes two parameters: a pointer to a callback function to run at exit,
and a pointer to untyped context data to be passed to that callback.</p>
<p>Callbacks are run in last-in first-out order.</p>
<p>The following <code>addon.cc</code> implements AtExit:</p>
<pre><code class="lang-cpp">// addon.cc
#undef NDEBUG
#include <assert.h>
#include <stdlib.h>
#include <node.h>
namespace demo {
using node::AtExit;
using v8::HandleScope;
using v8::Isolate;
using v8::Local;
using v8::Object;
static char cookie[] = "yum yum";
static int at_exit_cb1_called = 0;
static int at_exit_cb2_called = 0;
static void at_exit_cb1(void* arg) {
Isolate* isolate = static_cast<Isolate*>(arg);
HandleScope scope(isolate);
Local<Object> obj = Object::New(isolate);
assert(!obj.IsEmpty()); // assert VM is still alive
assert(obj->IsObject());
at_exit_cb1_called++;
}
static void at_exit_cb2(void* arg) {
assert(arg == static_cast<void*>(cookie));
at_exit_cb2_called++;
}
static void sanity_check(void*) {
assert(at_exit_cb1_called == 1);
assert(at_exit_cb2_called == 2);
}
void init(Local<Object> exports) {
AtExit(sanity_check);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb1, exports->GetIsolate());
}
NODE_MODULE(addon, init);
} // namespace demo
</code></pre>
<p>Test in JavaScript by running:</p>
<pre><code class="lang-js">// test.js
const addon = require('./build/Release/addon');
</code></pre>
<!-- [end-include:addons.md] -->
<!-- [start-include:assert.md] -->
<h1>Assert<span><a class="mark" href="#assert_assert" id="assert_assert">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>The <code>assert</code> module provides a simple set of assertion tests that can be used to
test invariants.</p>
<h2>assert(value[, message])<span><a class="mark" href="#assert_assert_value_message" id="assert_assert_value_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><ul>
<li><code>value</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>An alias of <a href="#assert_assert_ok_value_message"><code>assert.ok()</code></a> .</p>
<pre><code class="lang-js">const assert = require('assert');
assert(true); // OK
assert(1); // OK
assert(false);
// throws "AssertionError: false == true"
assert(0);
// throws "AssertionError: 0 == true"
assert(false, 'it\'s false');
// throws "AssertionError: it's false"
</code></pre>
<h2>assert.deepEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_deepequal_actual_expected_message" id="assert_assert_deepequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters.
Primitive values are compared with the equal comparison operator ( <code>==</code> ).</p>
<p>Only enumerable "own" properties are considered. The <code>deepEqual()</code>
implementation does not test object prototypes, attached symbols, or
non-enumerable properties. This can lead to some potentially surprising
results. For example, the following example does not throw an <code>AssertionError</code>
because the properties on the <a href="errors.html#errors_class_error"><code>Error</code></a> object are non-enumerable:</p>
<pre><code class="lang-js">// WARNING: This does not throw an AssertionError!
assert.deepEqual(Error('a'), Error('b'));
</code></pre>
<p>"Deep" equality means that the enumerable "own" properties of child objects
are evaluated also:</p>
<pre><code class="lang-js">const assert = require('assert');
const obj1 = {
a : {
b : 1
}
};
const obj2 = {
a : {
b : 2
}
};
const obj3 = {
a : {
b : 1
}
}
const obj4 = Object.create(obj1);
assert.deepEqual(obj1, obj1);
// OK, object is equal to itself
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }
// values of b are different
assert.deepEqual(obj1, obj3);
// OK, objects are equal
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
// Prototypes are ignored
</code></pre>
<p>If the values are not equal, an <code>AssertionError</code> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned.</p>
<h2>assert.deepStrictEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_deepstrictequal_actual_expected_message" id="assert_assert_deepstrictequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v1.2.0</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Generally identical to <code>assert.deepEqual()</code> with two exceptions. First,
primitive values are compared using the strict equality operator ( <code>===</code> ).
Second, object comparisons include a strict equality check of their prototypes.</p>
<pre><code class="lang-js">const assert = require('assert');
assert.deepEqual({a:1}, {a:'1'});
// OK, because 1 == '1'
assert.deepStrictEqual({a:1}, {a:'1'});
// AssertionError: { a: 1 } deepStrictEqual { a: '1' }
// because 1 !== '1' using strict equality
</code></pre>
<p>If the values are not equal, an <code>AssertionError</code> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned.</p>
<h2>assert.doesNotThrow(block[, error][, message])<span><a class="mark" href="#assert_assert_doesnotthrow_block_error_message" id="assert_assert_doesnotthrow_block_error_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>block</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Asserts that the function <code>block</code> does not throw an error. See
<a href="#assert_assert_throws_block_error_message"><code>assert.throws()</code></a> for more details.</p>
<p>When <code>assert.doesNotThrow()</code> is called, it will immediately call the <code>block</code>
function.</p>
<p>If an error is thrown and it is the same type as that specified by the <code>error</code>
parameter, then an <code>AssertionError</code> is thrown. If the error is of a different
type, or if the <code>error</code> parameter is undefined, the error is propagated back
to the caller.</p>
<p>The following, for instance, will throw the <a href="errors.html#errors_class_typeerror"><code>TypeError</code></a> because there is no
matching error type in the assertion:</p>
<pre><code class="lang-js">assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
SyntaxError
);
</code></pre>
<p>However, the following will result in an <code>AssertionError</code> with the message
'Got unwanted exception (TypeError)..':</p>
<pre><code class="lang-js">assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError
);
</code></pre>
<p>If an <code>AssertionError</code> is thrown and a value is provided for the <code>message</code>
parameter, the value of <code>message</code> will be appended to the <code>AssertionError</code>
message:</p>
<pre><code class="lang-js">assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError,
'Whoops'
);
// Throws: AssertionError: Got unwanted exception (TypeError). Whoops
</code></pre>
<h2>assert.equal(actual, expected[, message])<span><a class="mark" href="#assert_assert_equal_actual_expected_message" id="assert_assert_equal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Tests shallow, coercive equality between the <code>actual</code> and <code>expected</code> parameters
using the equal comparison operator ( <code>==</code> ).</p>
<pre><code class="lang-js">const assert = require('assert');
assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'
assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({a: {b: 1}}, {a: {b: 1}});
//AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
</code></pre>
<p>If the values are not equal, an <code>AssertionError</code> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned.</p>
<h2>assert.fail(actual, expected, message, operator)<span><a class="mark" href="#assert_assert_fail_actual_expected_message_operator" id="assert_assert_fail_actual_expected_message_operator">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
<p>Throws an <code>AssertionError</code>. If <code>message</code> is falsy, the error message is set as
the values of <code>actual</code> and <code>expected</code> separated by the provided <code>operator</code>.
Otherwise, the error message is the value of <code>message</code>.</p>
<pre><code class="lang-js">const assert = require('assert');
assert.fail(1, 2, undefined, '>');
// AssertionError: 1 > 2
assert.fail(1, 2, 'whoops', '>');
// AssertionError: whoops
</code></pre>
<h2>assert.ifError(value)<span><a class="mark" href="#assert_assert_iferror_value" id="assert_assert_iferror_value">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.97</span>
</div><ul>
<li><code>value</code> <span class="type"><any></span></li>
</ul>
<p>Throws <code>value</code> if <code>value</code> is truthy. This is useful when testing the <code>error</code>
argument in callbacks.</p>
<pre><code class="lang-js">const assert = require('assert');
assert.ifError(0); // OK
assert.ifError(1); // Throws 1
assert.ifError('error') // Throws 'error'
assert.ifError(new Error()); // Throws Error
</code></pre>
<h2>assert.notDeepEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_notdeepequal_actual_expected_message" id="assert_assert_notdeepequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Tests for any deep inequality. Opposite of <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a>.</p>
<pre><code class="lang-js">const assert = require('assert');
const obj1 = {
a : {
b : 1
}
};
const obj2 = {
a : {
b : 2
}
};
const obj3 = {
a : {
b : 1
}
};
const obj4 = Object.create(obj1);
assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj2);
// OK, obj1 and obj2 are not deeply equal
assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj4);
// OK, obj1 and obj4 are not deeply equal
</code></pre>
<p>If the values are deeply equal, an <code>AssertionError</code> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned.</p>
<h2>assert.notDeepStrictEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_notdeepstrictequal_actual_expected_message" id="assert_assert_notdeepstrictequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v1.2.0</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Tests for deep strict inequality. Opposite of <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p>
<pre><code class="lang-js">const assert = require('assert');
assert.notDeepEqual({a:1}, {a:'1'});
// AssertionError: { a: 1 } notDeepEqual { a: '1' }
assert.notDeepStrictEqual({a:1}, {a:'1'});
// OK
</code></pre>
<p>If the values are deeply and strictly equal, an <code>AssertionError</code> is thrown
with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If
the <code>message</code> parameter is undefined, a default error message is assigned.</p>
<h2>assert.notEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_notequal_actual_expected_message" id="assert_assert_notequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Tests shallow, coercive inequality with the not equal comparison operator
( <code>!=</code> ).</p>
<pre><code class="lang-js">const assert = require('assert');
assert.notEqual(1, 2);
// OK
assert.notEqual(1, 1);
// AssertionError: 1 != 1
assert.notEqual(1, '1');
// AssertionError: 1 != '1'
</code></pre>
<p>If the values are equal, an <code>AssertionError</code> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned.</p>
<h2>assert.notStrictEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_notstrictequal_actual_expected_message" id="assert_assert_notstrictequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Tests strict inequality as determined by the strict not equal operator
( <code>!==</code> ).</p>
<pre><code class="lang-js">const assert = require('assert');
assert.notStrictEqual(1, 2);
// OK
assert.notStrictEqual(1, 1);
// AssertionError: 1 !== 1
assert.notStrictEqual(1, '1');
// OK
</code></pre>
<p>If the values are strictly equal, an <code>AssertionError</code> is thrown with a
<code>message</code> property set equal to the value of the <code>message</code> parameter. If the
<code>message</code> parameter is undefined, a default error message is assigned.</p>
<h2>assert.ok(value[, message])<span><a class="mark" href="#assert_assert_ok_value_message" id="assert_assert_ok_value_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>value</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Tests if <code>value</code> is truthy. It is equivalent to
<code>assert.equal(!!value, true, message)</code>.</p>
<p>If <code>value</code> is not truthy, an <code>AssertionError</code> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is <code>undefined</code>, a default error message is assigned.</p>
<pre><code class="lang-js">const assert = require('assert');
assert.ok(true); // OK
assert.ok(1); // OK
assert.ok(false);
// throws "AssertionError: false == true"
assert.ok(0);
// throws "AssertionError: 0 == true"
assert.ok(false, 'it\'s false');
// throws "AssertionError: it's false"
</code></pre>
<h2>assert.strictEqual(actual, expected[, message])<span><a class="mark" href="#assert_assert_strictequal_actual_expected_message" id="assert_assert_strictequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>actual</code> <span class="type"><any></span></li>
<li><code>expected</code> <span class="type"><any></span></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Tests strict equality as determined by the strict equality operator ( <code>===</code> ).</p>
<pre><code class="lang-js">const assert = require('assert');
assert.strictEqual(1, 2);
// AssertionError: 1 === 2
assert.strictEqual(1, 1);
// OK
assert.strictEqual(1, '1');
// AssertionError: 1 === '1'
</code></pre>
<p>If the values are not strictly equal, an <code>AssertionError</code> is thrown with a
<code>message</code> property set equal to the value of the <code>message</code> parameter. If the
<code>message</code> parameter is undefined, a default error message is assigned.</p>
<h2>assert.throws(block[, error][, message])<span><a class="mark" href="#assert_assert_throws_block_error_message" id="assert_assert_throws_block_error_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><ul>
<li><code>block</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>message</code> <span class="type"><any></span></li>
</ul>
<p>Expects the function <code>block</code> to throw an error.</p>
<p>If specified, <code>error</code> can be a constructor, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, or validation
function.</p>
<p>If specified, <code>message</code> will be the message provided by the <code>AssertionError</code> if
the block fails to throw.</p>
<p>Validate instanceof using constructor:</p>
<pre><code class="lang-js">assert.throws(
() => {
throw new Error('Wrong value');
},
Error
);
</code></pre>
<p>Validate error message using <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>:</p>
<pre><code class="lang-js">assert.throws(
() => {
throw new Error('Wrong value');
},
/value/
);
</code></pre>
<p>Custom error validation:</p>
<pre><code class="lang-js">assert.throws(
() => {
throw new Error('Wrong value');
},
function(err) {
if ( (err instanceof Error) && /value/.test(err) ) {
return true;
}
},
'unexpected error'
);
</code></pre>
<p>Note that <code>error</code> can not be a string. If a string is provided as the second
argument, then <code>error</code> is assumed to be omitted and the string will be used for
<code>message</code> instead. This can lead to easy-to-miss mistakes:</p>
<pre><code class="lang-js">// THIS IS A MISTAKE! DO NOT DO THIS!
assert.throws(myFunction, 'missing foo', 'did not throw with expected message');
// Do this instead.
assert.throws(myFunction, /missing foo/, 'did not throw with expected message');
</code></pre>
<!-- [end-include:assert.md] -->
<!-- [start-include:buffer.md] -->
<h1>Buffer<span><a class="mark" href="#buffer_buffer" id="buffer_buffer">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>Prior to the introduction of <code>TypedArray</code> in ECMAScript 2015 (ES6), the
JavaScript language had no mechanism for reading or manipulating streams
of binary data. The <code>Buffer</code> class was introduced as part of the Node.js
API to make it possible to interact with octet streams in the context of things
like TCP streams and file system operations.</p>
<p>Now that <code>TypedArray</code> has been added in ES6, the <code>Buffer</code> class implements the
<code>Uint8Array</code> API in a manner that is more optimized and suitable for Node.js'
use cases.</p>
<p>Instances of the <code>Buffer</code> class are similar to arrays of integers but
correspond to fixed-sized, raw memory allocations outside the V8 heap.
The size of the <code>Buffer</code> is established when it is created and cannot be
resized.</p>
<p>The <code>Buffer</code> class is a global within Node.js, making it unlikely that one
would need to ever use <code>require('buffer').Buffer</code>.</p>
<pre><code class="lang-js">const buf1 = new Buffer(10);
// creates a buffer of length 10
// This is the same as Buffer.allocUnsafe(10), and the returned
// Buffer instance might contain old data that needs to be
// overwritten using either fill() or write().
const buf2 = new Buffer([1,2,3]);
// creates a buffer containing [01, 02, 03]
// This is the same as Buffer.from([1,2,3]).
const buf3 = new Buffer('test');
// creates a buffer containing ASCII bytes [74, 65, 73, 74]
// This is the same as Buffer.from('test').
const buf4 = new Buffer('tést', 'utf8');
// creates a buffer containing UTF8 bytes [74, c3, a9, 73, 74]
// This is the same as Buffer.from('tést', 'utf8').
const buf5 = Buffer.alloc(10);
// Creates a zero-filled Buffer of length 10.
const buf6 = Buffer.alloc(10, 1);
// Creates a Buffer of length 10, filled with 0x01.
const buf7 = Buffer.allocUnsafe(10);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using either fill() or write().
const buf8 = Buffer.from([1,2,3]);
// Creates a Buffer containing [01, 02, 03].
const buf9 = Buffer.from('test');
// Creates a Buffer containing ASCII bytes [74, 65, 73, 74].
const buf8 = Buffer.from('tést', 'utf8');
// Creates a Buffer containing UTF8 bytes [74, c3, a9, 73, 74].
</code></pre>
<h2><code>Buffer.from()</code>, <code>Buffer.alloc()</code>, and <code>Buffer.allocUnsafe()</code><span><a class="mark" href="#buffer_buffer_from_buffer_alloc_and_buffer_allocunsafe" id="buffer_buffer_from_buffer_alloc_and_buffer_allocunsafe">#</a></span></h2>
<p>Historically, <code>Buffer</code> instances have been created using the <code>Buffer</code>
constructor function, which allocates the returned <code>Buffer</code>
differently based on what arguments are provided:</p>
<ul>
<li>Passing a number as the first argument to <code>Buffer()</code> (e.g. <code>new Buffer(10)</code>),
allocates a new <code>Buffer</code> object of the specified size. The memory allocated
for such <code>Buffer</code> instances is <em>not</em> initialized and <em>can contain sensitive
data</em>. Such <code>Buffer</code> objects <em>must</em> be initialized <em>manually</em> by using either
<a href="#buffer_buf_fill_value_offset_end"><code>buf.fill(0)</code></a> or by writing to the <code>Buffer</code> completely. While this
behavior is <em>intentional</em> to improve performance, development experience has
demonstrated that a more explicit distinction is required between creating a
fast-but-uninitialized <code>Buffer</code> versus creating a slower-but-safer <code>Buffer</code>.</li>
<li>Passing a string, array, or <code>Buffer</code> as the first argument copies the
passed object's data into the <code>Buffer</code>.</li>
<li>Passing an <code>ArrayBuffer</code> returns a <code>Buffer</code> that shares allocated memory with
the given <code>ArrayBuffer</code>.</li>
</ul>
<p>Because the behavior of <code>new Buffer()</code> changes significantly based on the type
of value passed as the first argument, applications that do not properly
validate the input arguments passed to <code>new Buffer()</code>, or that fail to
appropriately initialize newly allocated <code>Buffer</code> content, can inadvertently
introduce security and reliability issues into their code.</p>
<p>To make the creation of <code>Buffer</code> objects more reliable and less error prone,
new <code>Buffer.from()</code>, <code>Buffer.alloc()</code>, and <code>Buffer.allocUnsafe()</code> methods have
been introduced as an alternative means of creating <code>Buffer</code> instances.</p>
<p><em>Developers should migrate all existing uses of the <code>new Buffer()</code> constructors
to one of these new APIs.</em></p>
<ul>
<li><a href="#buffer_class_method_buffer_from_array"><code>Buffer.from(array)</code></a> returns a new <code>Buffer</code> containing
a <em>copy</em> of the provided octets.</li>
<li><a href="#buffer_class_method_buffer_from_arraybuffer"><code>Buffer.from(arrayBuffer)</code></a> returns a new <code>Buffer</code>
that <em>shares</em> the same allocated memory as the given <code>ArrayBuffer</code>.</li>
<li><a href="#buffer_class_method_buffer_from_buffer"><code>Buffer.from(buffer)</code></a> returns a new <code>Buffer</code>
containing a <em>copy</em> of the contents of the given <code>Buffer</code>.</li>
<li><a href="#buffer_class_method_buffer_from_str_encoding"><code>Buffer.from(str[, encoding])</code></a> returns a new <code>Buffer</code>
containing a <em>copy</em> of the provided string.</li>
<li><a href="#buffer_class_method_buffer_alloc_size_fill_encoding"><code>Buffer.alloc(size[, fill[, encoding]])</code></a> returns a "filled"
<code>Buffer</code> instance of the specified size. This method can be significantly
slower than <a href="#buffer_class_method_buffer_allocunsafe_size"><code>Buffer.allocUnsafe(size)</code></a> but ensures
that newly created <code>Buffer</code> instances never contain old and potentially
sensitive data.</li>
<li><a href="#buffer_class_method_buffer_allocunsafe_size"><code>Buffer.allocUnsafe(size)</code></a> and
<a href="#buffer_class_method_buffer_allocunsafeslow_size"><code>Buffer.allocUnsafeSlow(size)</code></a> each return a
new <code>Buffer</code> of the specified <code>size</code> whose content <em>must</em> be initialized
using either <a href="#buffer_buf_fill_value_offset_end"><code>buf.fill(0)</code></a> or written to completely.</li>
</ul>
<p><code>Buffer</code> instances returned by <code>Buffer.allocUnsafe(size)</code> <em>may</em> be allocated
off a shared internal memory pool if <code>size</code> is less than or equal to half
<code>Buffer.poolSize</code>. Instances returned by <code>Buffer.allocUnsafeSlow(size)</code> <em>never</em>
use the shared internal memory pool.</p>
<h3>What makes <code>Buffer.allocUnsafe(size)</code> and <code>Buffer.allocUnsafeSlow(size)</code> "unsafe"?<span><a class="mark" href="#buffer_what_makes_buffer_allocunsafe_size_and_buffer_allocunsafeslow_size_unsafe" id="buffer_what_makes_buffer_allocunsafe_size_and_buffer_allocunsafeslow_size_unsafe">#</a></span></h3>
<p>When calling <code>Buffer.allocUnsafe()</code> (and <code>Buffer.allocUnsafeSlow()</code>), the
segment of allocated memory is <em>uninitialized</em> (it is not zeroed-out). While
this design makes the allocation of memory quite fast, the allocated segment of
memory might contain old data that is potentially sensitive. Using a <code>Buffer</code>
created by <code>Buffer.allocUnsafe()</code> without <em>completely</em> overwriting the memory
can allow this old data to be leaked when the <code>Buffer</code> memory is read.</p>
<p>While there are clear performance advantages to using <code>Buffer.allocUnsafe()</code>,
extra care <em>must</em> be taken in order to avoid introducing security
vulnerabilities into an application.</p>
<h2>Buffers and Character Encodings<span><a class="mark" href="#buffer_buffers_and_character_encodings" id="buffer_buffers_and_character_encodings">#</a></span></h2>
<p>Buffers are commonly used to represent sequences of encoded characters
such as UTF8, UCS2, Base64 or even Hex-encoded data. It is possible to
convert back and forth between Buffers and ordinary JavaScript string objects
by using an explicit encoding method.</p>
<pre><code class="lang-js">const buf = new Buffer('hello world', 'ascii');
console.log(buf.toString('hex'));
// prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// prints: aGVsbG8gd29ybGQ=
</code></pre>
<p>The character encodings currently supported by Node.js include:</p>
<ul>
<li><p><code>'ascii'</code> - for 7-bit ASCII data only. This encoding method is very fast and
will strip the high bit if set.</p>
</li>
<li><p><code>'utf8'</code> - Multibyte encoded Unicode characters. Many web pages and other
document formats use UTF-8.</p>
</li>
<li><p><code>'utf16le'</code> - 2 or 4 bytes, little-endian encoded Unicode characters.
Surrogate pairs (U+10000 to U+10FFFF) are supported.</p>
</li>
<li><p><code>'ucs2'</code> - Alias of <code>'utf16le'</code>.</p>
</li>
<li><p><code>'base64'</code> - Base64 string encoding. When creating a buffer from a string,
this encoding will also correctly accept "URL and Filename Safe Alphabet" as
specified in <a href="https://tools.ietf.org/html/rfc4648#section-5">RFC 4648, Section 5</a>.</p>
</li>
<li><p><code>'binary'</code> - A way of encoding the buffer into a one-byte (<code>latin-1</code>)
encoded string. The string <code>'latin-1'</code> is not supported. Instead, pass
<code>'binary'</code> to use <code>'latin-1'</code> encoding.</p>
</li>
<li><p><code>'hex'</code> - Encode each byte as two hexadecimal characters.</p>
</li>
</ul>
<h2>Buffers and TypedArray<span><a class="mark" href="#buffer_buffers_and_typedarray" id="buffer_buffers_and_typedarray">#</a></span></h2>
<p>Buffers are also <code>Uint8Array</code> TypedArray instances. However, there are subtle
incompatibilities with the TypedArray specification in ECMAScript 2015. For
instance, while <code>ArrayBuffer#slice()</code> creates a copy of the slice,
the implementation of <a href="#buffer_buf_slice_start_end"><code>Buffer#slice()</code></a> creates a view over the
existing Buffer without copying, making <code>Buffer#slice()</code> far more efficient.</p>
<p>It is also possible to create new TypedArray instances from a <code>Buffer</code> with the
following caveats:</p>
<ol>
<li><p>The Buffer instances's memory is copied to the TypedArray, not shared.</p>
</li>
<li><p>The Buffer's memory is interpreted as an array of distinct elements, and not
as a byte array of the target type. That is,
<code>new Uint32Array(new Buffer([1,2,3,4]))</code> creates a 4-element <code>Uint32Array</code>
with elements <code>[1,2,3,4]</code>, not a <code>Uint32Array</code> with a single element
<code>[0x1020304]</code> or <code>[0x4030201]</code>.</p>
</li>
</ol>
<p>It is possible to create a new Buffer that shares the same allocated memory as
a TypedArray instance by using the TypeArray objects <code>.buffer</code> property:</p>
<pre><code class="lang-js">const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
const buf1 = new Buffer(arr); // copies the buffer
const buf2 = new Buffer(arr.buffer); // shares the memory with arr;
console.log(buf1);
// Prints: <Buffer 88 a0>, copied buffer has only two elements
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
</code></pre>
<p>Note that when creating a Buffer using the TypeArray's <code>.buffer</code>, it is not
currently possible to use only a portion of the underlying <code>ArrayBuffer</code>. To
create a Buffer that uses only a part of the <code>ArrayBuffer</code>, use the
<a href="#buffer_buf_slice_start_end"><code>buf.slice()</code></a> function after the Buffer is created:</p>
<pre><code class="lang-js">const arr = new Uint16Array(20);
const buf = new Buffer(arr.buffer).slice(0, 16);
console.log(buf.length);
// Prints: 16
</code></pre>
<p>The <code>Buffer.from()</code> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/from"><code>TypedArray.from()</code></a> (e.g.<code>Uint8Array.from()</code>) have
different signatures and implementations. Specifically, the TypedArray variants
accept a second argument that is a mapping function that is invoked on every
element of the typed array:</p>
<ul>
<li><code>TypedArray.from(source[, mapFn[, thisArg]])</code></li>
</ul>
<p>The <code>Buffer.from()</code> method, however, does not support the use of a mapping
function:</p>
<ul>
<li><a href="#buffer_class_method_buffer_from_array"><code>Buffer.from(array)</code></a></li>
<li><a href="#buffer_class_method_buffer_from_buffer"><code>Buffer.from(buffer)</code></a></li>
<li><a href="#buffer_class_method_buffer_from_arraybuffer"><code>Buffer.from(arrayBuffer)</code></a></li>
<li><a href="#buffer_class_method_buffer_from_str_encoding"><code>Buffer.from(str[, encoding])</code></a></li>
</ul>
<h2>Buffers and ES6 iteration<span><a class="mark" href="#buffer_buffers_and_es6_iteration" id="buffer_buffers_and_es6_iteration">#</a></span></h2>
<p>Buffers can be iterated over using the ECMAScript 2015 (ES6) <code>for..of</code> syntax:</p>
<pre><code class="lang-js">const buf = new Buffer([1, 2, 3]);
for (var b of buf)
console.log(b)
// Prints:
// 1
// 2
// 3
</code></pre>
<p>Additionally, the <a href="#buffer_buf_values"><code>buf.values()</code></a>, <a href="#buffer_buf_keys"><code>buf.keys()</code></a>, and
<a href="#buffer_buf_entries"><code>buf.entries()</code></a> methods can be used to create iterators.</p>
<h2>The <code>--zero-fill-buffers</code> command line option<span><a class="mark" href="#buffer_the_zero_fill_buffers_command_line_option" id="buffer_the_zero_fill_buffers_command_line_option">#</a></span></h2>
<p>Node.js can be started using the <code>--zero-fill-buffers</code> command line option to
force all newly allocated <code>Buffer</code> and <code>SlowBuffer</code> instances created using
either <code>new Buffer(size)</code> and <code>new SlowBuffer(size)</code> to be <em>automatically
zero-filled</em> upon creation. Use of this flag <em>changes the default behavior</em> of
these methods and <em>can have a significant impact</em> on performance. Use of the
<code>--zero-fill-buffers</code> option is recommended only when absolutely necessary to
enforce that newly allocated <code>Buffer</code> instances cannot contain potentially
sensitive data.</p>
<pre><code>$ node --zero-fill-buffers
> Buffer(5);
<Buffer 00 00 00 00 00>
</code></pre><h2>Class: Buffer<span><a class="mark" href="#buffer_class_buffer" id="buffer_class_buffer">#</a></span></h2>
<p>The Buffer class is a global type for dealing with binary data directly.
It can be constructed in a variety of ways.</p>
<h3>new Buffer(array)<span><a class="mark" href="#buffer_new_buffer_array" id="buffer_new_buffer_array">#</a></span></h3>
<div class="signature"><ul>
<li><code>array</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a></li>
</ul>
</div><p>Allocates a new Buffer using an <code>array</code> of octets.</p>
<pre><code class="lang-js">const buf = new Buffer([0x62,0x75,0x66,0x66,0x65,0x72]);
// creates a new Buffer containing ASCII bytes
// ['b','u','f','f','e','r']
</code></pre>
<h3>new Buffer(buffer)<span><a class="mark" href="#buffer_new_buffer_buffer" id="buffer_new_buffer_buffer">#</a></span></h3>
<div class="signature"><ul>
<li><code>buffer</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
</ul>
</div><p>Copies the passed <code>buffer</code> data onto a new <code>Buffer</code> instance.</p>
<pre><code class="lang-js">const buf1 = new Buffer('buffer');
const buf2 = new Buffer(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// 'auffer'
console.log(buf2.toString());
// 'buffer' (copy is not changed)
</code></pre>
<h3>new Buffer(arrayBuffer)<span><a class="mark" href="#buffer_new_buffer_arraybuffer" id="buffer_new_buffer_arraybuffer">#</a></span></h3>
<div class="signature"><ul>
<li><code>arrayBuffer</code> - The <code>.buffer</code> property of a <code>TypedArray</code> or a <code>new
ArrayBuffer()</code></li>
</ul>
</div><p>When passed a reference to the <code>.buffer</code> property of a <code>TypedArray</code> instance,
the newly created Buffer will share the same allocated memory as the
TypedArray.</p>
<pre><code class="lang-js">const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
const buf = new Buffer(arr.buffer); // shares the memory with arr;
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// changing the TypdArray changes the Buffer also
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
</code></pre>
<h3>new Buffer(size)<span><a class="mark" href="#buffer_new_buffer_size" id="buffer_new_buffer_size">#</a></span></h3>
<div class="signature"><ul>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Allocates a new Buffer of <code>size</code> bytes. The <code>size</code> must be less than
or equal to the value of <code>require('buffer').kMaxLength</code> (on 64-bit
architectures, <code>kMaxLength</code> is <code>(2^31)-1</code>). Otherwise, a <a href="errors.html#errors_class_rangeerror"><code>RangeError</code></a> is
thrown. If a <code>size</code> less than 0 is specified, a zero-length Buffer will be
created.</p>
<p>Unlike <code>ArrayBuffers</code>, the underlying memory for Buffer instances created in
this way is not initialized. The contents of a newly created <code>Buffer</code> are
unknown and could contain sensitive data. Use <a href="#buffer_buf_fill_value_offset_end"><code>buf.fill(0)</code></a> to initialize a
Buffer to zeroes.</p>
<pre><code class="lang-js">const buf = new Buffer(5);
console.log(buf);
// <Buffer 78 e0 82 02 01>
// (octets will be different, every time)
buf.fill(0);
console.log(buf);
// <Buffer 00 00 00 00 00>
</code></pre>
<h3>new Buffer(str[, encoding])<span><a class="mark" href="#buffer_new_buffer_str_encoding" id="buffer_new_buffer_str_encoding">#</a></span></h3>
<div class="signature"><ul>
<li><code>str</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> String to encode.</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Default: <code>'utf8'</code></li>
</ul>
</div><p>Creates a new Buffer containing the given JavaScript string <code>str</code>. If
provided, the <code>encoding</code> parameter identifies the strings character encoding.</p>
<pre><code class="lang-js">const buf1 = new Buffer('this is a tést');
console.log(buf1.toString());
// prints: this is a tést
console.log(buf1.toString('ascii'));
// prints: this is a tC)st
const buf2 = new Buffer('7468697320697320612074c3a97374', 'hex');
console.log(buf2.toString());
// prints: this is a tést
</code></pre>
<h3>Class Method: Buffer.alloc(size[, fill[, encoding]])<span><a class="mark" href="#buffer_class_method_buffer_alloc_size_fill_encoding" id="buffer_class_method_buffer_alloc_size_fill_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.5.0</span>
</div><ul>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
<li><code>fill</code> <span class="type"><Value></span> Default: <code>undefined</code></li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Default: <code>utf8</code></li>
</ul>
<p>Allocates a new <code>Buffer</code> of <code>size</code> bytes. If <code>fill</code> is <code>undefined</code>, the
<code>Buffer</code> will be <em>zero-filled</em>.</p>
<pre><code class="lang-js">const buf = Buffer.alloc(5);
console.log(buf);
// <Buffer 00 00 00 00 00>
</code></pre>
<p>The <code>size</code> must be less than or equal to the value of
<code>require('buffer').kMaxLength</code> (on 64-bit architectures, <code>kMaxLength</code> is
<code>(2^31)-1</code>). Otherwise, a <a href="errors.html#errors_class_rangeerror"><code>RangeError</code></a> is thrown. If a <code>size</code> less than 0
is specified, a zero-length <code>Buffer</code> will be created.</p>
<p>If <code>fill</code> is specified, the allocated <code>Buffer</code> will be initialized by calling
<code>buf.fill(fill)</code>. See [<code>buf.fill()</code>][] for more information.</p>
<pre><code class="lang-js">const buf = Buffer.alloc(5, 'a');
console.log(buf);
// <Buffer 61 61 61 61 61>
</code></pre>
<p>If both <code>fill</code> and <code>encoding</code> are specified, the allocated <code>Buffer</code> will be
initialized by calling <code>buf.fill(fill, encoding)</code>. For example:</p>
<pre><code class="lang-js">const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
// <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
</code></pre>
<p>Calling <code>Buffer.alloc(size)</code> can be significantly slower than the alternative
<code>Buffer.allocUnsafe(size)</code> but ensures that the newly created <code>Buffer</code> instance
contents will <em>never contain sensitive data</em>.</p>
<p>A <code>TypeError</code> will be thrown if <code>size</code> is not a number.</p>
<h3>Class Method: Buffer.allocUnsafe(size)<span><a class="mark" href="#buffer_class_method_buffer_allocunsafe_size" id="buffer_class_method_buffer_allocunsafe_size">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.5.0</span>
</div><ul>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
<p>Allocates a new <em>non-zero-filled</em> <code>Buffer</code> of <code>size</code> bytes. The <code>size</code> must
be less than or equal to the value of <code>require('buffer').kMaxLength</code> (on 64-bit
architectures, <code>kMaxLength</code> is <code>(2^31)-1</code>). Otherwise, a <a href="errors.html#errors_class_rangeerror"><code>RangeError</code></a> is
thrown. If a <code>size</code> less than 0 is specified, a zero-length <code>Buffer</code> will be
created.</p>
<p>The underlying memory for <code>Buffer</code> instances created in this way is <em>not
initialized</em>. The contents of the newly created <code>Buffer</code> are unknown and
<em>may contain sensitive data</em>. Use <a href="#buffer_buf_fill_value_offset_end"><code>buf.fill(0)</code></a> to initialize such
<code>Buffer</code> instances to zeroes.</p>
<pre><code class="lang-js">const buf = Buffer.allocUnsafe(5);
console.log(buf);
// <Buffer 78 e0 82 02 01>
// (octets will be different, every time)
buf.fill(0);
console.log(buf);
// <Buffer 00 00 00 00 00>
</code></pre>
<p>A <code>TypeError</code> will be thrown if <code>size</code> is not a number.</p>
<p>Note that the <code>Buffer</code> module pre-allocates an internal <code>Buffer</code> instance of
size <code>Buffer.poolSize</code> that is used as a pool for the fast allocation of new
<code>Buffer</code> instances created using <code>Buffer.allocUnsafe(size)</code> (and the
<code>new Buffer(size)</code> constructor) only when <code>size</code> is less than or equal to
<code>Buffer.poolSize >> 1</code> (floor of <code>Buffer.poolSize</code> divided by two). The default
value of <code>Buffer.poolSize</code> is <code>8192</code> but can be modified.</p>
<p>Use of this pre-allocated internal memory pool is a key difference between
calling <code>Buffer.alloc(size, fill)</code> vs. <code>Buffer.allocUnsafe(size).fill(fill)</code>.
Specifically, <code>Buffer.alloc(size, fill)</code> will <em>never</em> use the internal Buffer
pool, while <code>Buffer.allocUnsafe(size).fill(fill)</code> <em>will</em> use the internal
Buffer pool if <code>size</code> is less than or equal to half <code>Buffer.poolSize</code>. The
difference is subtle but can be important when an application requires the
additional performance that <code>Buffer.allocUnsafe(size)</code> provides.</p>
<h3>Class Method: Buffer.allocUnsafeSlow(size)<span><a class="mark" href="#buffer_class_method_buffer_allocunsafeslow_size" id="buffer_class_method_buffer_allocunsafeslow_size">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.5.0</span>
</div><ul>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
<p>Allocates a new <em>non-zero-filled</em> and non-pooled <code>Buffer</code> of <code>size</code> bytes. The
<code>size</code> must be less than or equal to the value of
<code>require('buffer').kMaxLength</code> (on 64-bit architectures, <code>kMaxLength</code> is
<code>(2^31)-1</code>). Otherwise, a <a href="errors.html#errors_class_rangeerror"><code>RangeError</code></a> is thrown. If a <code>size</code> less than 0
is specified, a zero-length <code>Buffer</code> will be created.</p>
<p>The underlying memory for <code>Buffer</code> instances created in this way is <em>not
initialized</em>. The contents of the newly created <code>Buffer</code> are unknown and
<em>may contain sensitive data</em>. Use <a href="#buffer_buf_fill_value_offset_end"><code>buf.fill(0)</code></a> to initialize such
<code>Buffer</code> instances to zeroes.</p>
<p>When using <code>Buffer.allocUnsafe()</code> to allocate new <code>Buffer</code> instances,
allocations under 4KB are, by default, sliced from a single pre-allocated
<code>Buffer</code>. This allows applications to avoid the garbage collection overhead of
creating many individually allocated Buffers. This approach improves both
performance and memory usage by eliminating the need to track and cleanup as
many <code>Persistent</code> objects.</p>
<p>However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled Buffer instance using <code>Buffer.allocUnsafeSlow()</code> then
copy out the relevant bits.</p>
<pre><code class="lang-js">// need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
const data = socket.read();
// allocate for retained data
const sb = Buffer.allocUnsafeSlow(10);
// copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
</code></pre>
<p>Use of <code>Buffer.allocUnsafeSlow()</code> should be used only as a last resort <em>after</em>
a developer has observed undue memory retention in their applications.</p>
<p>A <code>TypeError</code> will be thrown if <code>size</code> is not a number.</p>
<h3>Class Method: Buffer.byteLength(string[, encoding])<span><a class="mark" href="#buffer_class_method_buffer_bytelength_string_encoding" id="buffer_class_method_buffer_bytelength_string_encoding">#</a></span></h3>
<div class="signature"><ul>
<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Default: <code>'utf8'</code></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Returns the actual byte length of a string. This is not the same as
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length"><code>String.prototype.length</code></a> since that returns the number of <em>characters</em> in
a string.</p>
<p><em>Note</em> that for <code>'base64'</code> and <code>'hex'</code>, this function assumes valid input. For
strings that contain non-Base64/Hex-encoded data (e.g. whitespace), the return
value might be greater than the length of a <code>Buffer</code> created from the string.</p>
<p>Example:</p>
<pre><code class="lang-js">const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
// ½ + ¼ = ¾: 9 characters, 12 bytes
</code></pre>
<h3>Class Method: Buffer.compare(buf1, buf2)<span><a class="mark" href="#buffer_class_method_buffer_compare_buf1_buf2" id="buffer_class_method_buffer_compare_buf1_buf2">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.13</span>
</div><ul>
<li><code>buf1</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
<li><code>buf2</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
<p>Compares <code>buf1</code> to <code>buf2</code> typically for the purpose of sorting arrays of
Buffers. This is equivalent is calling <a href="#buffer_buf_compare_otherbuffer"><code>buf1.compare(buf2)</code></a>.</p>
<pre><code class="lang-js">const arr = [Buffer('1234'), Buffer('0123')];
arr.sort(Buffer.compare);
</code></pre>
<h3>Class Method: Buffer.concat(list[, totalLength])<span><a class="mark" href="#buffer_class_method_buffer_concat_list_totallength" id="buffer_class_method_buffer_concat_list_totallength">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.11</span>
</div><ul>
<li><code>list</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> List of Buffer objects to concat</li>
<li><code>totalLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Total length of the Buffers in the list when concatenated</li>
<li>Returns: <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
</ul>
<p>Returns a new Buffer which is the result of concatenating all the Buffers in
the <code>list</code> together.</p>
<p>If the list has no items, or if the <code>totalLength</code> is 0, then a new zero-length
Buffer is returned.</p>
<p>If <code>totalLength</code> is not provided, it is calculated from the Buffers in the
<code>list</code>. This, however, adds an additional loop to the function, so it is faster
to provide the length explicitly.</p>
<p>Example: build a single Buffer from a list of three Buffers:</p>
<pre><code class="lang-js">const buf1 = new Buffer(10).fill(0);
const buf2 = new Buffer(14).fill(0);
const buf3 = new Buffer(18).fill(0);
const totalLength = buf1.length + buf2.length + buf3.length;
console.log(totalLength);
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
console.log(bufA.length);
// 42
// <Buffer 00 00 00 00 ...>
// 42
</code></pre>
<h3>Class Method: Buffer.from(array)<span><a class="mark" href="#buffer_class_method_buffer_from_array" id="buffer_class_method_buffer_from_array">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.5.0</span>
</div><ul>
<li><code>array</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a></li>
</ul>
<p>Allocates a new <code>Buffer</code> using an <code>array</code> of octets.</p>
<pre><code class="lang-js">const buf = Buffer.from([0x62,0x75,0x66,0x66,0x65,0x72]);
// creates a new Buffer containing ASCII bytes
// ['b','u','f','f','e','r']
</code></pre>
<p>A <code>TypeError</code> will be thrown if <code>array</code> is not an <code>Array</code>.</p>
<h3>Class Method: Buffer.from(arrayBuffer)<span><a class="mark" href="#buffer_class_method_buffer_from_arraybuffer" id="buffer_class_method_buffer_from_arraybuffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.5.0</span>
</div><ul>
<li><code>arrayBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> The <code>.buffer</code> property of a <code>TypedArray</code> or
a <code>new ArrayBuffer()</code></li>
</ul>
<p>When passed a reference to the <code>.buffer</code> property of a <code>TypedArray</code> instance,
the newly created <code>Buffer</code> will share the same allocated memory as the
TypedArray.</p>
<pre><code class="lang-js">const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
const buf = Buffer.from(arr.buffer); // shares the memory with arr;
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// changing the TypedArray changes the Buffer also
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
</code></pre>
<p>A <code>TypeError</code> will be thrown if <code>arrayBuffer</code> is not an <code>ArrayBuffer</code>.</p>
<h3>Class Method: Buffer.from(buffer)<span><a class="mark" href="#buffer_class_method_buffer_from_buffer" id="buffer_class_method_buffer_from_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.5.0</span>
</div><ul>
<li><code>buffer</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
</ul>
<p>Copies the passed <code>buffer</code> data onto a new <code>Buffer</code> instance.</p>
<pre><code class="lang-js">const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// 'auffer'
console.log(buf2.toString());
// 'buffer' (copy is not changed)
</code></pre>
<p>A <code>TypeError</code> will be thrown if <code>buffer</code> is not a <code>Buffer</code>.</p>
<h3>Class Method: Buffer.from(str[, encoding])<span><a class="mark" href="#buffer_class_method_buffer_from_str_encoding" id="buffer_class_method_buffer_from_str_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.5.0</span>
</div><ul>
<li><code>str</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> String to encode.</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Encoding to use, Default: <code>'utf8'</code></li>
</ul>
<p>Creates a new <code>Buffer</code> containing the given JavaScript string <code>str</code>. If
provided, the <code>encoding</code> parameter identifies the character encoding.
If not provided, <code>encoding</code> defaults to <code>'utf8'</code>.</p>
<pre><code class="lang-js">const buf1 = Buffer.from('this is a tést');
console.log(buf1.toString());
// prints: this is a tést
console.log(buf1.toString('ascii'));
// prints: this is a tC)st
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf2.toString());
// prints: this is a tést
</code></pre>
<p>A <code>TypeError</code> will be thrown if <code>str</code> is not a string.</p>
<h3>Class Method: Buffer.isBuffer(obj)<span><a class="mark" href="#buffer_class_method_buffer_isbuffer_obj" id="buffer_class_method_buffer_isbuffer_obj">#</a></span></h3>
<div class="signature"><ul>
<li><code>obj</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
</div><p>Returns 'true' if <code>obj</code> is a Buffer.</p>
<h3>Class Method: Buffer.isEncoding(encoding)<span><a class="mark" href="#buffer_class_method_buffer_isencoding_encoding" id="buffer_class_method_buffer_isencoding_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The encoding string to test</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>Returns true if the <code>encoding</code> is a valid encoding argument, or false
otherwise.</p>
<h3>buf[index]<span><a class="mark" href="#buffer_buf_index" id="buffer_buf_index">#</a></span></h3>
<div class="api_metadata">
</div><p>The index operator <code>[index]</code> can be used to get and set the octet at position
<code>index</code> in the Buffer. The values refer to individual bytes, so the legal value
range is between <code>0x00</code> and <code>0xFF</code> (hex) or <code>0</code> and <code>255</code> (decimal).</p>
<p>Example: copy an ASCII string into a Buffer, one byte at a time:</p>
<pre><code class="lang-js">const str = "Node.js";
const buf = new Buffer(str.length);
for (var i = 0; i < str.length ; i++) {
buf[i] = str.charCodeAt(i);
}
console.log(buf.toString('ascii'));
// Prints: Node.js
</code></pre>
<h3>buf.compare(otherBuffer)<span><a class="mark" href="#buffer_buf_compare_otherbuffer" id="buffer_buf_compare_otherbuffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.13</span>
</div><ul>
<li><code>otherBuffer</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
<p>Compares two Buffer instances and returns a number indicating whether <code>buf</code>
comes before, after, or is the same as the <code>otherBuffer</code> in sort order.
Comparison is based on the actual sequence of bytes in each Buffer.</p>
<ul>
<li><code>0</code> is returned if <code>otherBuffer</code> is the same as <code>buf</code></li>
<li><code>1</code> is returned if <code>otherBuffer</code> should come <em>before</em> <code>buf</code> when sorted.</li>
<li><code>-1</code> is returned if <code>otherBuffer</code> should come <em>after</em> <code>buf</code> when sorted.</li>
</ul>
<pre><code class="lang-js">const buf1 = new Buffer('ABC');
const buf2 = new Buffer('BCD');
const buf3 = new Buffer('ABCD');
console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: -1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
[buf1, buf2, buf3].sort(Buffer.compare);
// produces sort order [buf1, buf3, buf2]
</code></pre>
<h3>buf.copy(targetBuffer[, targetStart[, sourceStart[, sourceEnd]]])<span><a class="mark" href="#buffer_buf_copy_targetbuffer_targetstart_sourcestart_sourceend" id="buffer_buf_copy_targetbuffer_targetstart_sourcestart_sourceend">#</a></span></h3>
<div class="signature"><ul>
<li><code>targetBuffer</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> Buffer to copy into</li>
<li><code>targetStart</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: 0</li>
<li><code>sourceStart</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: 0</li>
<li><code>sourceEnd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: <code>buffer.length</code></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The number of bytes copied.</li>
</ul>
</div><p>Copies data from a region of this Buffer to a region in the target Buffer even
if the target memory region overlaps with the source.</p>
<p>Example: build two Buffers, then copy <code>buf1</code> from byte 16 through byte 19
into <code>buf2</code>, starting at the 8th byte in <code>buf2</code>.</p>
<pre><code class="lang-js">const buf1 = new Buffer(26);
const buf2 = new Buffer(26).fill('!');
for (var i = 0 ; i < 26 ; i++) {
buf1[i] = i + 97; // 97 is ASCII a
}
buf1.copy(buf2, 8, 16, 20);
console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
</code></pre>
<p>Example: Build a single Buffer, then copy data from one region to an overlapping
region in the same Buffer</p>
<pre><code class="lang-js">const buf = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
buf[i] = i + 97; // 97 is ASCII a
}
buf.copy(buf, 0, 4, 10);
console.log(buf.toString());
// efghijghijklmnopqrstuvwxyz
</code></pre>
<h3>buf.entries()<span><a class="mark" href="#buffer_buf_entries" id="buffer_buf_entries">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.1.0</span>
</div><ul>
<li>Returns: <span class="type"><Iterator></span></li>
</ul>
<p>Creates and returns an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols">iterator</a> of <code>[index, byte]</code> pairs from the Buffer
contents.</p>
<pre><code class="lang-js">const buf = new Buffer('buffer');
for (var pair of buf.entries()) {
console.log(pair);
}
// prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
</code></pre>
<h3>buf.equals(otherBuffer)<span><a class="mark" href="#buffer_buf_equals_otherbuffer" id="buffer_buf_equals_otherbuffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><ul>
<li><code>otherBuffer</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>Returns a boolean indicating whether <code>this</code> and <code>otherBuffer</code> have exactly the
same bytes.</p>
<pre><code class="lang-js">const buf1 = new Buffer('ABC');
const buf2 = new Buffer('414243', 'hex');
const buf3 = new Buffer('ABCD');
console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
</code></pre>
<h3>buf.fill(value[, offset[, end]])<span><a class="mark" href="#buffer_buf_fill_value_offset_end" id="buffer_buf_fill_value_offset_end">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: 0</li>
<li><code>end</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: <code>buffer.length</code></li>
<li>Returns: <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
</ul>
<p>Fills the Buffer with the specified value. If the <code>offset</code> and <code>end</code> are not
given it will fill the entire Buffer. The method returns a reference to the
Buffer so calls can be chained.</p>
<pre><code class="lang-js">const b = new Buffer(50).fill('h');
console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
</code></pre>
<h3>buf.indexOf(value[, byteOffset][, encoding])<span><a class="mark" href="#buffer_buf_indexof_value_byteoffset_encoding" id="buffer_buf_indexof_value_byteoffset_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.5.0</span>
</div><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
<li><code>byteOffset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: 0</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Default: <code>'utf8'</code></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
<p>Operates similar to <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf"><code>Array#indexOf()</code></a> in that it returns either the
starting index position of <code>value</code> in Buffer or <code>-1</code> if the Buffer does not
contain <code>value</code>. The <code>value</code> can be a String, Buffer or Number. Strings are by
default interpreted as UTF8. Buffers will use the entire Buffer (to compare a
partial Buffer use <a href="#buffer_buf_slice_start_end"><code>buf.slice()</code></a>). Numbers will be interpreted as unsigned 8-bit
integer values between <code>0</code> and <code>255</code>.</p>
<pre><code class="lang-js">const buf = new Buffer('this is a buffer');
buf.indexOf('this');
// returns 0
buf.indexOf('is');
// returns 2
buf.indexOf(new Buffer('a buffer'));
// returns 8
buf.indexOf(97); // ascii for 'a'
// returns 8
buf.indexOf(new Buffer('a buffer example'));
// returns -1
buf.indexOf(new Buffer('a buffer example').slice(0,8));
// returns 8
const utf16Buffer = new Buffer('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
utf16Buffer.indexOf('\u03a3', 0, 'ucs2');
// returns 4
utf16Buffer.indexOf('\u03a3', -4, 'ucs2');
// returns 6
</code></pre>
<h3>buf.keys()<span><a class="mark" href="#buffer_buf_keys" id="buffer_buf_keys">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.1.0</span>
</div><ul>
<li>Returns: <span class="type"><Iterator></span></li>
</ul>
<p>Creates and returns an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols">iterator</a> of Buffer keys (indices).</p>
<pre><code class="lang-js">const buf = new Buffer('buffer');
for (var key of buf.keys()) {
console.log(key);
}
// prints:
// 0
// 1
// 2
// 3
// 4
// 5
</code></pre>
<h3>buf.length<span><a class="mark" href="#buffer_buf_length" id="buffer_buf_length">#</a></span></h3>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Returns the amount of memory allocated for the Buffer in number of bytes. Note
that this does not necessarily reflect the amount of usable data within the
Buffer. For instance, in the example below, a Buffer with 1234 bytes is
allocated, but only 11 ASCII bytes are written.</p>
<pre><code class="lang-js">const buf = new Buffer(1234);
console.log(buf.length);
// Prints: 1234
buf.write('some string', 0, 'ascii');
console.log(buf.length);
// Prints: 1234
</code></pre>
<p>While the <code>length</code> property is not immutable, changing the value of <code>length</code>
can result in undefined and inconsistent behavior. Applications that wish to
modify the length of a Buffer should therefore treat <code>length</code> as read-only and
use <a href="#buffer_buf_slice_start_end"><code>buf.slice()</code></a> to create a new Buffer.</p>
<pre><code class="lang-js">var buf = new Buffer(10);
buf.write('abcdefghj', 0, 'ascii');
console.log(buf.length);
// Prints: 10
buf = buf.slice(0,5);
console.log(buf.length);
// Prints: 5
</code></pre>
<h3>buf.readDoubleBE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readdoublebe_offset_noassert" id="buffer_buf_readdoublebe_offset_noassert">#</a></span></h3>
<h3>buf.readDoubleLE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readdoublele_offset_noassert" id="buffer_buf_readdoublele_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 8</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Reads a 64-bit double from the Buffer at the specified <code>offset</code> with specified
endian format (<code>readDoubleBE()</code> returns big endian, <code>readDoubleLE()</code> returns
little endian).</p>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<pre><code class="lang-js">const buf = new Buffer([1,2,3,4,5,6,7,8]);
buf.readDoubleBE();
// Returns: 8.20788039913184e-304
buf.readDoubleLE();
// Returns: 5.447603722011605e-270
buf.readDoubleLE(1);
// throws RangeError: Index out of range
buf.readDoubleLE(1, true); // Warning: reads passed end of buffer!
// Segmentation fault! don't do this!
</code></pre>
<h3>buf.readFloatBE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readfloatbe_offset_noassert" id="buffer_buf_readfloatbe_offset_noassert">#</a></span></h3>
<h3>buf.readFloatLE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readfloatle_offset_noassert" id="buffer_buf_readfloatle_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 4</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Reads a 32-bit float from the Buffer at the specified <code>offset</code> with specified
endian format (<code>readFloatBE()</code> returns big endian, <code>readFloatLE()</code> returns
little endian).</p>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<pre><code class="lang-js">const buf = new Buffer([1,2,3,4]);
buf.readFloatBE();
// Returns: 2.387939260590663e-38
buf.readFloatLE();
// Returns: 1.539989614439558e-36
buf.readFloatLE(1);
// throws RangeError: Index out of range
buf.readFloatLE(1, true); // Warning: reads passed end of buffer!
// Segmentation fault! don't do this!
</code></pre>
<h3>buf.readInt8(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readint8_offset_noassert" id="buffer_buf_readint8_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 1</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Reads a signed 8-bit integer from the Buffer at the specified <code>offset</code>.</p>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<p>Integers read from the Buffer are interpreted as two's complement signed values.</p>
<pre><code class="lang-js">const buf = new Buffer([1,-2,3,4]);
buf.readInt8(0);
// returns 1
buf.readInt8(1);
// returns -2
</code></pre>
<h3>buf.readInt16BE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readint16be_offset_noassert" id="buffer_buf_readint16be_offset_noassert">#</a></span></h3>
<h3>buf.readInt16LE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readint16le_offset_noassert" id="buffer_buf_readint16le_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 2</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Reads a signed 16-bit integer from the Buffer at the specified <code>offset</code> with
the specified endian format (<code>readInt16BE()</code> returns big endian,
<code>readInt16LE()</code> returns little endian).</p>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<p>Integers read from the Buffer are interpreted as two's complement signed values.</p>
<pre><code class="lang-js">const buf = new Buffer([1,-2,3,4]);
buf.readInt16BE();
// returns 510
buf.readInt16LE(1);
// returns 1022
</code></pre>
<h3>buf.readInt32BE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readint32be_offset_noassert" id="buffer_buf_readint32be_offset_noassert">#</a></span></h3>
<h3>buf.readInt32LE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readint32le_offset_noassert" id="buffer_buf_readint32le_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 4</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Reads a signed 32-bit integer from the Buffer at the specified <code>offset</code> with
the specified endian format (<code>readInt32BE()</code> returns big endian,
<code>readInt32LE()</code> returns little endian).</p>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<p>Integers read from the Buffer are interpreted as two's complement signed values.</p>
<pre><code class="lang-js">const buf = new Buffer([1,-2,3,4]);
buf.readInt32BE();
// returns 33424132
buf.readInt32LE();
// returns 67370497
buf.readInt32LE(1);
// throws RangeError: Index out of range
</code></pre>
<h3>buf.readIntBE(offset, byteLength[, noAssert])<span><a class="mark" href="#buffer_buf_readintbe_offset_bytelength_noassert" id="buffer_buf_readintbe_offset_bytelength_noassert">#</a></span></h3>
<h3>buf.readIntLE(offset, byteLength[, noAssert])<span><a class="mark" href="#buffer_buf_readintle_offset_bytelength_noassert" id="buffer_buf_readintle_offset_bytelength_noassert">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - byteLength</code></li>
<li><code>byteLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 < byteLength <= 6</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
<p>Reads <code>byteLength</code> number of bytes from the Buffer at the specified <code>offset</code>
and interprets the result as a two's complement signed value. Supports up to 48
bits of accuracy. For example:</p>
<pre><code class="lang-js">const buf = new Buffer(6);
buf.writeUInt16LE(0x90ab, 0);
buf.writeUInt32LE(0x12345678, 2);
buf.readIntLE(0, 6).toString(16); // Specify 6 bytes (48 bits)
// Returns: '1234567890ab'
buf.readIntBE(0, 6).toString(16);
// Returns: -546f87a9cbee
</code></pre>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<h3>buf.readUInt8(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readuint8_offset_noassert" id="buffer_buf_readuint8_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 1</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Reads an unsigned 8-bit integer from the Buffer at the specified <code>offset</code>.</p>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<pre><code class="lang-js">const buf = new Buffer([1,-2,3,4]);
buf.readUInt8(0);
// returns 1
buf.readUInt8(1);
// returns 254
</code></pre>
<h3>buf.readUInt16BE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readuint16be_offset_noassert" id="buffer_buf_readuint16be_offset_noassert">#</a></span></h3>
<h3>buf.readUInt16LE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readuint16le_offset_noassert" id="buffer_buf_readuint16le_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 2</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Reads an unsigned 16-bit integer from the Buffer at the specified <code>offset</code> with
specified endian format (<code>readUInt16BE()</code> returns big endian,
<code>readUInt16LE()</code> returns little endian).</p>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<p>Example:</p>
<pre><code class="lang-js">const buf = new Buffer([0x3, 0x4, 0x23, 0x42]);
buf.readUInt16BE(0);
// Returns: 0x0304
buf.readUInt16LE(0);
// Returns: 0x0403
buf.readUInt16BE(1);
// Returns: 0x0423
buf.readUInt16LE(1);
// Returns: 0x2304
buf.readUInt16BE(2);
// Returns: 0x2342
buf.readUInt16LE(2);
// Returns: 0x4223
</code></pre>
<h3>buf.readUInt32BE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readuint32be_offset_noassert" id="buffer_buf_readuint32be_offset_noassert">#</a></span></h3>
<h3>buf.readUInt32LE(offset[, noAssert])<span><a class="mark" href="#buffer_buf_readuint32le_offset_noassert" id="buffer_buf_readuint32le_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 4</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>Reads an unsigned 32-bit integer from the Buffer at the specified <code>offset</code> with
specified endian format (<code>readUInt32BE()</code> returns big endian,
<code>readUInt32LE()</code> returns little endian).</p>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<p>Example:</p>
<pre><code class="lang-js">const buf = new Buffer([0x3, 0x4, 0x23, 0x42]);
buf.readUInt32BE(0);
// Returns: 0x03042342
console.log(buf.readUInt32LE(0));
// Returns: 0x42230403
</code></pre>
<h3>buf.readUIntBE(offset, byteLength[, noAssert])<span><a class="mark" href="#buffer_buf_readuintbe_offset_bytelength_noassert" id="buffer_buf_readuintbe_offset_bytelength_noassert">#</a></span></h3>
<h3>buf.readUIntLE(offset, byteLength[, noAssert])<span><a class="mark" href="#buffer_buf_readuintle_offset_bytelength_noassert" id="buffer_buf_readuintle_offset_bytelength_noassert">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><ul>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - byteLength</code></li>
<li><code>byteLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 < byteLength <= 6</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
<p>Reads <code>byteLength</code> number of bytes from the Buffer at the specified <code>offset</code>
and interprets the result as an unsigned integer. Supports up to 48
bits of accuracy. For example:</p>
<pre><code class="lang-js">const buf = new Buffer(6);
buf.writeUInt16LE(0x90ab, 0);
buf.writeUInt32LE(0x12345678, 2);
buf.readUIntLE(0, 6).toString(16); // Specify 6 bytes (48 bits)
// Returns: '1234567890ab'
buf.readUIntBE(0, 6).toString(16);
// Returns: ab9078563412
</code></pre>
<p>Setting <code>noAssert</code> to <code>true</code> skips validation of the <code>offset</code>. This allows the
<code>offset</code> to be beyond the end of the Buffer.</p>
<h3>buf.slice([start[, end]])<span><a class="mark" href="#buffer_buf_slice_start_end" id="buffer_buf_slice_start_end">#</a></span></h3>
<div class="signature"><ul>
<li><code>start</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: 0</li>
<li><code>end</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: <code>buffer.length</code></li>
<li>Returns: <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
</ul>
</div><p>Returns a new Buffer that references the same memory as the original, but
offset and cropped by the <code>start</code> and <code>end</code> indices.</p>
<p><strong>Note that modifying the new Buffer slice will modify the memory in the
original Buffer because the allocated memory of the two objects overlap.</strong></p>
<p>Example: build a Buffer with the ASCII alphabet, take a slice, then modify one
byte from the original Buffer.</p>
<pre><code class="lang-js">const buf1 = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
buf1[i] = i + 97; // 97 is ASCII a
}
const buf2 = buf1.slice(0, 3);
buf2.toString('ascii', 0, buf2.length);
// Returns: 'abc'
buf1[0] = 33;
buf2.toString('ascii', 0, buf2.length);
// Returns : '!bc'
</code></pre>
<p>Specifying negative indexes causes the slice to be generated relative to the
end of the Buffer rather than the beginning.</p>
<pre><code class="lang-js">const buf = new Buffer('buffer');
buf.slice(-6, -1).toString();
// Returns 'buffe', equivalent to buf.slice(0, 5)
buf.slice(-6, -2).toString();
// Returns 'buff', equivalent to buf.slice(0, 4)
buf.slice(-5, -2).toString();
// Returns 'uff', equivalent to buf.slice(1, 4)
</code></pre>
<h3>buf.toString([encoding[, start[, end]]])<span><a class="mark" href="#buffer_buf_tostring_encoding_start_end" id="buffer_buf_tostring_encoding_start_end">#</a></span></h3>
<div class="signature"><ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Default: <code>'utf8'</code></li>
<li><code>start</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: 0</li>
<li><code>end</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: <code>buffer.length</code></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
</div><p>Decodes and returns a string from the Buffer data using the specified
character set <code>encoding</code>.</p>
<pre><code class="lang-js">const buf = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
buf[i] = i + 97; // 97 is ASCII a
}
buf.toString('ascii');
// Returns: 'abcdefghijklmnopqrstuvwxyz'
buf.toString('ascii',0,5);
// Returns: 'abcde'
buf.toString('utf8',0,5);
// Returns: 'abcde'
buf.toString(undefined,0,5);
// Returns: 'abcde', encoding defaults to 'utf8'
</code></pre>
<h3>buf.toJSON()<span><a class="mark" href="#buffer_buf_tojson" id="buffer_buf_tojson">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.2</span>
</div><ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Returns a JSON representation of the Buffer instance. <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify"><code>JSON.stringify()</code></a>
implicitly calls this function when stringifying a Buffer instance.</p>
<p>Example:</p>
<pre><code class="lang-js">const buf = new Buffer('test');
const json = JSON.stringify(buf);
console.log(json);
// Prints: '{"type":"Buffer","data":[116,101,115,116]}'
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer'
? new Buffer(value.data)
: value;
});
console.log(copy.toString());
// Prints: 'test'
</code></pre>
<h3>buf.values()<span><a class="mark" href="#buffer_buf_values" id="buffer_buf_values">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.1.0</span>
</div><ul>
<li>Returns: <span class="type"><Iterator></span></li>
</ul>
<p>Creates and returns an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols">iterator</a> for Buffer values (bytes). This function is
called automatically when the Buffer is used in a <code>for..of</code> statement.</p>
<pre><code class="lang-js">const buf = new Buffer('buffer');
for (var value of buf.values()) {
console.log(value);
}
// prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (var value of buf) {
console.log(value);
}
// prints:
// 98
// 117
// 102
// 102
// 101
// 114
</code></pre>
<h3>buf.write(string[, offset[, length]][, encoding])<span><a class="mark" href="#buffer_buf_write_string_offset_length_encoding" id="buffer_buf_write_string_offset_length_encoding">#</a></span></h3>
<div class="signature"><ul>
<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Bytes to be written to buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: 0</li>
<li><code>length</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: <code>buffer.length - offset</code></li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Default: <code>'utf8'</code></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Numbers of bytes written</li>
</ul>
</div><p>Writes <code>string</code> to the Buffer at <code>offset</code> using the given <code>encoding</code>.
The <code>length</code> parameter is the number of bytes to write. If the Buffer did not
contain enough space to fit the entire string, only a partial amount of the
string will be written however, it will not write only partially encoded
characters.</p>
<pre><code class="lang-js">const buf = new Buffer(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
// Prints: 12 bytes: ½ + ¼ = ¾
</code></pre>
<h3>buf.writeDoubleBE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writedoublebe_value_offset_noassert" id="buffer_buf_writedoublebe_value_offset_noassert">#</a></span></h3>
<h3>buf.writeDoubleLE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writedoublele_value_offset_noassert" id="buffer_buf_writedoublele_value_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 8</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code> with specified endian
format (<code>writeDoubleBE()</code> writes big endian, <code>writeDoubleLE()</code> writes little
endian). The <code>value</code> argument <em>should</em> be a valid 64-bit double. Behavior is
not defined when <code>value</code> is anything other than a 64-bit double.</p>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>Example:</p>
<pre><code class="lang-js">const buf = new Buffer(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);
console.log(buf);
// Prints: <Buffer 43 eb d5 b7 dd f9 5f d7>
buf.writeDoubleLE(0xdeadbeefcafebabe, 0);
console.log(buf);
// Prints: <Buffer d7 5f f9 dd b7 d5 eb 43>
</code></pre>
<h3>buf.writeFloatBE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writefloatbe_value_offset_noassert" id="buffer_buf_writefloatbe_value_offset_noassert">#</a></span></h3>
<h3>buf.writeFloatLE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writefloatle_value_offset_noassert" id="buffer_buf_writefloatle_value_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 4</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code> with specified endian
format (<code>writeFloatBE()</code> writes big endian, <code>writeFloatLE()</code> writes little
endian). Behavior is not defined when <code>value</code> is anything other than a 32-bit
float.</p>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>Example:</p>
<pre><code class="lang-js">const buf = new Buffer(4);
buf.writeFloatBE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer 4f 4a fe bb>
buf.writeFloatLE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
</code></pre>
<h3>buf.writeInt8(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeint8_value_offset_noassert" id="buffer_buf_writeint8_value_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 1</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code>. The <code>value</code> should be a
valid signed 8-bit integer. Behavior is not defined when <code>value</code> is anything
other than a signed 8-bit integer.</p>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>The <code>value</code> is interpreted and written as a two's complement signed integer.</p>
<pre><code class="lang-js">const buf = new Buffer(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
console.log(buf);
// Prints: <Buffer 02 fe>
</code></pre>
<h3>buf.writeInt16BE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeint16be_value_offset_noassert" id="buffer_buf_writeint16be_value_offset_noassert">#</a></span></h3>
<h3>buf.writeInt16LE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeint16le_value_offset_noassert" id="buffer_buf_writeint16le_value_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 2</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code> with specified endian
format (<code>writeInt16BE()</code> writes big endian, <code>writeInt16LE()</code> writes little
endian). The <code>value</code> should be a valid signed 16-bit integer. Behavior is
not defined when <code>value</code> is anything other than a signed 16-bit integer.</p>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>The <code>value</code> is interpreted and written as a two's complement signed integer.</p>
<pre><code class="lang-js">const buf = new Buffer(4);
buf.writeInt16BE(0x0102,0);
buf.writeInt16LE(0x0304,2);
console.log(buf);
// Prints: <Buffer 01 02 04 03>
</code></pre>
<h3>buf.writeInt32BE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeint32be_value_offset_noassert" id="buffer_buf_writeint32be_value_offset_noassert">#</a></span></h3>
<h3>buf.writeInt32LE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeint32le_value_offset_noassert" id="buffer_buf_writeint32le_value_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 4</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code> with specified endian
format (<code>writeInt32BE()</code> writes big endian, <code>writeInt32LE()</code> writes little
endian). The <code>value</code> should be a valid signed 32-bit integer. Behavior is
not defined when <code>value</code> is anything other than a signed 32-bit integer.</p>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>The <code>value</code> is interpreted and written as a two's complement signed integer.</p>
<pre><code class="lang-js">const buf = new Buffer(8);
buf.writeInt32BE(0x01020304,0);
buf.writeInt32LE(0x05060708,4);
console.log(buf);
// Prints: <Buffer 01 02 03 04 08 07 06 05>
</code></pre>
<h3>buf.writeIntBE(value, offset, byteLength[, noAssert])<span><a class="mark" href="#buffer_buf_writeintbe_value_offset_bytelength_noassert" id="buffer_buf_writeintbe_value_offset_bytelength_noassert">#</a></span></h3>
<h3>buf.writeIntLE(value, offset, byteLength[, noAssert])<span><a class="mark" href="#buffer_buf_writeintle_value_offset_bytelength_noassert" id="buffer_buf_writeintle_value_offset_bytelength_noassert">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - byteLength</code></li>
<li><code>byteLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 < byteLength <= 6</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
<p>Writes <code>value</code> to the Buffer at the specified <code>offset</code> and <code>byteLength</code>.
Supports up to 48 bits of accuracy. For example:</p>
<pre><code class="lang-js">const buf1 = new Buffer(6);
buf1.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf1);
// Prints: <Buffer 12 34 56 78 90 ab>
const buf2 = new Buffer(6);
buf2.writeUIntLE(0x1234567890ab, 0, 6);
console.log(buf2);
// Prints: <Buffer ab 90 78 56 34 12>
</code></pre>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>Behavior is not defined when <code>value</code> is anything other than an integer.</p>
<h3>buf.writeUInt8(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeuint8_value_offset_noassert" id="buffer_buf_writeuint8_value_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 1</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code>. The <code>value</code> should be a
valid unsigned 8-bit integer. Behavior is not defined when <code>value</code> is anything
other than an unsigned 8-bit integer.</p>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>Example:</p>
<pre><code class="lang-js">const buf = new Buffer(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
console.log(buf);
// Prints: <Buffer 03 04 23 42>
</code></pre>
<h3>buf.writeUInt16BE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeuint16be_value_offset_noassert" id="buffer_buf_writeuint16be_value_offset_noassert">#</a></span></h3>
<h3>buf.writeUInt16LE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeuint16le_value_offset_noassert" id="buffer_buf_writeuint16le_value_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 2</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code> with specified endian
format (<code>writeUInt16BE()</code> writes big endian, <code>writeUInt16LE()</code> writes little
endian). The <code>value</code> should be a valid unsigned 16-bit integer. Behavior is
not defined when <code>value</code> is anything other than an unsigned 16-bit integer.</p>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>Example:</p>
<pre><code class="lang-js">const buf = new Buffer(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer de ad be ef>
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer ad de ef be>
</code></pre>
<h3>buf.writeUInt32BE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeuint32be_value_offset_noassert" id="buffer_buf_writeuint32be_value_offset_noassert">#</a></span></h3>
<h3>buf.writeUInt32LE(value, offset[, noAssert])<span><a class="mark" href="#buffer_buf_writeuint32le_value_offset_noassert" id="buffer_buf_writeuint32le_value_offset_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - 4</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code> with specified endian
format (<code>writeUInt32BE()</code> writes big endian, <code>writeUInt32LE()</code> writes little
endian). The <code>value</code> should be a valid unsigned 32-bit integer. Behavior is
not defined when <code>value</code> is anything other than an unsigned 32-bit integer.</p>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>Example:</p>
<pre><code class="lang-js">const buf = new Buffer(4);
buf.writeUInt32BE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer fe ed fa ce>
buf.writeUInt32LE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer ce fa ed fe>
</code></pre>
<h3>buf.writeUIntBE(value, offset, byteLength[, noAssert])<span><a class="mark" href="#buffer_buf_writeuintbe_value_offset_bytelength_noassert" id="buffer_buf_writeuintbe_value_offset_bytelength_noassert">#</a></span></h3>
<h3>buf.writeUIntLE(value, offset, byteLength[, noAssert])<span><a class="mark" href="#buffer_buf_writeuintle_value_offset_bytelength_noassert" id="buffer_buf_writeuintle_value_offset_bytelength_noassert">#</a></span></h3>
<div class="signature"><ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Bytes to be written to Buffer</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 <= offset <= buf.length - byteLength</code></li>
<li><code>byteLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> <code>0 < byteLength <= 6</code></li>
<li><code>noAssert</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default: false</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The offset plus the number of written bytes</li>
</ul>
</div><p>Writes <code>value</code> to the Buffer at the specified <code>offset</code> and <code>byteLength</code>.
Supports up to 48 bits of accuracy. For example:</p>
<pre><code class="lang-js">const buf = new Buffer(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
</code></pre>
<p>Set <code>noAssert</code> to true to skip validation of <code>value</code> and <code>offset</code>. This means
that <code>value</code> may be too large for the specific function and <code>offset</code> may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.</p>
<p>Behavior is not defined when <code>value</code> is anything other than an unsigned integer.</p>
<h2>buffer.INSPECT_MAX_BYTES<span><a class="mark" href="#buffer_buffer_inspect_max_bytes" id="buffer_buffer_inspect_max_bytes">#</a></span></h2>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default: 50</li>
</ul>
</div><p>Returns the maximum number of bytes that will be returned when
<code>buffer.inspect()</code> is called. This can be overridden by user modules. See
<a href="util.html#util_util_inspect_object_options"><code>util.inspect()</code></a> for more details on <code>buffer.inspect()</code> behavior.</p>
<p>Note that this is a property on the <code>buffer</code> module as returned by
<code>require('buffer')</code>, not on the Buffer global or a Buffer instance.</p>
<h2>Class: SlowBuffer<span><a class="mark" href="#buffer_class_slowbuffer" id="buffer_class_slowbuffer">#</a></span></h2>
<p>Returns an un-pooled <code>Buffer</code>.</p>
<p>In order to avoid the garbage collection overhead of creating many individually
allocated Buffers, by default allocations under 4KB are sliced from a single
larger allocated object. This approach improves both performance and memory
usage since v8 does not need to track and cleanup as many <code>Persistent</code> objects.</p>
<p>In the case where a developer may need to retain a small chunk of memory from a
pool for an indeterminate amount of time, it may be appropriate to create an
un-pooled Buffer instance using <code>SlowBuffer</code> then copy out the relevant bits.</p>
<pre><code class="lang-js">// need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
var data = socket.read();
// allocate for retained data
var sb = new SlowBuffer(10);
// copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
</code></pre>
<p>Use of <code>SlowBuffer</code> should be used only as a last resort <em>after</em> a developer
has observed undue memory retention in their applications.</p>
<h3>new SlowBuffer(size)<span><a class="mark" href="#buffer_new_slowbuffer_size" id="buffer_new_slowbuffer_size">#</a></span></h3>
<div class="signature"><ul>
<li><code>size</code> Number</li>
</ul>
</div><p>Allocates a new <code>SlowBuffer</code> of <code>size</code> bytes. The <code>size</code> must be less than
or equal to the value of <code>require('buffer').kMaxLength</code> (on 64-bit
architectures, <code>kMaxLength</code> is <code>(2^31)-1</code>). Otherwise, a <a href="errors.html#errors_class_rangeerror"><code>RangeError</code></a> is
thrown. If a <code>size</code> less than 0 is specified, a zero-length <code>SlowBuffer</code> will be
created.</p>
<p>The underlying memory for <code>SlowBuffer</code> instances is <em>not initialized</em>. The
contents of a newly created <code>SlowBuffer</code> are unknown and could contain
sensitive data. Use <a href="#buffer_buf_fill_value_offset_end"><code>buf.fill(0)</code></a> to initialize a <code>SlowBuffer</code> to zeroes.</p>
<pre><code class="lang-js">const SlowBuffer = require('buffer').SlowBuffer;
const buf = new SlowBuffer(5);
console.log(buf);
// <Buffer 78 e0 82 02 01>
// (octets will be different, every time)
buf.fill(0);
console.log(buf);
// <Buffer 00 00 00 00 00>
</code></pre>
<!-- [end-include:buffer.md] -->
<!-- [start-include:child_process.md] -->
<h1>Child Process<span><a class="mark" href="#child_process_child_process" id="child_process_child_process">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>The <code>child_process</code> module provides the ability to spawn child processes in
a manner that is similar, but not identical, to <a href="http://linux.die.net/man/3/popen"><code>popen(3)</code></a>. This capability
is primarily provided by the <code>child_process.spawn()</code> function:</p>
<pre><code class="lang-js">const spawn = require('child_process').spawn;
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
</code></pre>
<p>By default, pipes for <code>stdin</code>, <code>stdout</code> and <code>stderr</code> are established between
the parent Node.js process and the spawned child. It is possible to stream data
through these pipes in a non-blocking way. <em>Note, however, that some programs
use line-buffered I/O internally. While that does not affect Node.js, it can
mean that data sent to the child process may not be immediately consumed.</em></p>
<p>The <code>child_process.spawn()</code> method spawns the child process asynchronously,
without blocking the Node.js event loop. The <code>child_process.spawnSync()</code>
function provides equivalent functionality in a synchronous manner that blocks
the event loop until the spawned process either exits or is terminated.</p>
<p>For convenience, the <code>child_process</code> module provides a handful of synchronous
and asynchronous alternatives to <a href="#child_process_child_process_spawn_command_args_options"><code>child_process.spawn()</code></a> and
<a href="#child_process_child_process_spawnsync_command_args_options"><code>child_process.spawnSync()</code></a>. <em>Note that each of these alternatives are
implemented on top of <code>child_process.spawn()</code> or <code>child_process.spawnSync()</code>.</em></p>
<ul>
<li><code>child_process.exec()</code>: spawns a shell and runs a command within that shell,
passing the <code>stdout</code> and <code>stderr</code> to a callback function when complete.</li>
<li><code>child_process.execFile()</code>: similar to <code>child_process.exec()</code> except that
it spawns the command directly without first spawning a shell.</li>
<li><code>child_process.fork()</code>: spawns a new Node.js process and invokes a
specified module with an IPC communication channel established that allows
sending messages between parent and child.</li>
<li><code>child_process.execSync()</code>: a synchronous version of
<code>child_process.exec()</code> that <em>will</em> block the Node.js event loop.</li>
<li><code>child_process.execFileSync()</code>: a synchronous version of
<code>child_process.execFile()</code> that <em>will</em> block the Node.js event loop.</li>
</ul>
<p>For certain use cases, such as automating shell scripts, the
<a href="#child_process_synchronous_process_creation">synchronous counterparts</a> may be more convenient. In many cases, however,
the synchronous methods can have significant impact on performance due to
stalling the event loop while spawned processes complete.</p>
<h2>Asynchronous Process Creation<span><a class="mark" href="#child_process_asynchronous_process_creation" id="child_process_asynchronous_process_creation">#</a></span></h2>
<p>The <code>child_process.spawn()</code>, <code>child_process.fork()</code>, <code>child_process.exec()</code>,
and <code>child_process.execFile()</code> methods all follow the idiomatic asynchronous
programming pattern typical of other Node.js APIs.</p>
<p>Each of the methods returns a <a href="#child_process_child_process"><code>ChildProcess</code></a> instance. These objects
implement the Node.js <a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a> API, allowing the parent process to
register listener functions that are called when certain events occur during
the life cycle of the child process.</p>
<p>The <code>child_process.exec()</code> and <code>child_process.execFile()</code> methods additionally
allow for an optional <code>callback</code> function to be specified that is invoked
when the child process terminates.</p>
<h3>Spawning <code>.bat</code> and <code>.cmd</code> files on Windows<span><a class="mark" href="#child_process_spawning_bat_and_cmd_files_on_windows" id="child_process_spawning_bat_and_cmd_files_on_windows">#</a></span></h3>
<p>The importance of the distinction between <code>child_process.exec()</code> and
<code>child_process.execFile()</code> can vary based on platform. On Unix-type operating
systems (Unix, Linux, OSX) <code>child_process.execFile()</code> can be more efficient
because it does not spawn a shell. On Windows, however, <code>.bat</code> and <code>.cmd</code>
files are not executable on their own without a terminal, and therefore cannot
be launched using <code>child_process.execFile()</code>. When running on Windows, <code>.bat</code>
and <code>.cmd</code> files can be invoked using <code>child_process.spawn()</code> with the <code>shell</code>
option set, with <code>child_process.exec()</code>, or by spawning <code>cmd.exe</code> and passing
the <code>.bat</code> or <code>.cmd</code> file as an argument (which is what the <code>shell</code> option and
<code>child_process.exec()</code> do).</p>
<pre><code class="lang-js">// On Windows Only ...
const spawn = require('child_process').spawn;
const bat = spawn('cmd.exe', ['/c', 'my.bat']);
bat.stdout.on('data', (data) => {
console.log(data);
});
bat.stderr.on('data', (data) => {
console.log(data);
});
bat.on('exit', (code) => {
console.log(`Child exited with code ${code}`);
});
// OR...
const exec = require('child_process').exec;
exec('my.bat', (err, stdout, stderr) => {
if (err) {
console.error(err);
return;
}
console.log(stdout);
});
</code></pre>
<h3>child_process.exec(command[, options][, callback])<span><a class="mark" href="#child_process_child_process_exec_command_options_callback" id="child_process_child_process_exec_command_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><code>command</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The command to run, with space-separated arguments</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>cwd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Current working directory of the child process</li>
<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Environment key-value pairs</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> (Default: 'utf8')</li>
<li><code>shell</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Shell to execute the command with
(Default: '/bin/sh' on UNIX, 'cmd.exe' on Windows, The shell should
understand the <code>-c</code> switch on UNIX or <code>/s /c</code> on Windows. On Windows,
command line parsing should be compatible with <code>cmd.exe</code>.)</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> (Default: 0)</li>
<li><code>maxBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> largest amount of data (in bytes) allowed on stdout or
stderr - if exceeded child process is killed (Default: <code>200*1024</code>)</li>
<li><code>killSignal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <span class="type"><Integer></span> (Default: 'SIGTERM')</li>
<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.)</li>
<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.)</li>
</ul>
</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> called with the output when process terminates<ul>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
<li><code>stdout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
<li><code>stderr</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
</ul>
</li>
<li>Returns: <a href="child_process.html#child_process_class_childprocess" class="type"><ChildProcess></a></li>
</ul>
<p>Spawns a shell then executes the <code>command</code> within that shell, buffering any
generated output.</p>
<p><strong>Note: Never pass unsanitised user input to this function. Any input
containing shell metacharacters may be used to trigger arbitrary command
execution.</strong></p>
<pre><code class="lang-js">const exec = require('child_process').exec;
exec('cat *.js bad_file | wc -l', (error, stdout, stderr) => {
if (error) {
console.error(`exec error: ${error}`);
return;
}
console.log(`stdout: ${stdout}`);
console.log(`stderr: ${stderr}`);
});
</code></pre>
<p>If a <code>callback</code> function is provided, it is called with the arguments
<code>(error, stdout, stderr)</code>. On success, <code>error</code> will be <code>null</code>. On error,
<code>error</code> will be an instance of <a href="errors.html#errors_class_error"><code>Error</code></a>. The <code>error.code</code> property will be
the exit code of the child process while <code>error.signal</code> will be set to the
signal that terminated the process. Any exit code other than <code>0</code> is considered
to be an error.</p>
<p>The <code>stdout</code> and <code>stderr</code> arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The <code>encoding</code> option
can be used to specify the character encoding used to decode the stdout and
stderr output. If <code>encoding</code> is <code>'buffer'</code>, or an unrecognized character
encoding, <code>Buffer</code> objects will be passed to the callback instead.</p>
<p>The <code>options</code> argument may be passed as the second argument to customize how
the process is spawned. The default options are:</p>
<pre><code class="lang-js">{
encoding: 'utf8',
timeout: 0,
maxBuffer: 200*1024,
killSignal: 'SIGTERM',
cwd: null,
env: null
}
</code></pre>
<p>If <code>timeout</code> is greater than <code>0</code>, the parent will send the the signal
identified by the <code>killSignal</code> property (the default is <code>'SIGTERM'</code>) if the
child runs longer than <code>timeout</code> milliseconds.</p>
<p>The <code>maxBuffer</code> option specifies the largest amount of data (in bytes) allowed
on stdout or stderr - if this value is exceeded then the child process is
terminated.</p>
<p><em>Note: Unlike the <code>exec()</code> POSIX system call, <code>child_process.exec()</code> does not
replace the existing process and uses a shell to execute the command.</em></p>
<h3>child_process.execFile(file[, args][, options][, callback])<span><a class="mark" href="#child_process_child_process_execfile_file_args_options_callback" id="child_process_child_process_execfile_file_args_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.91</span>
</div><ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The name or path of the executable file to run</li>
<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> List of string arguments</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>cwd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Current working directory of the child process</li>
<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Environment key-value pairs</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> (Default: 'utf8')</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> (Default: 0)</li>
<li><code>maxBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> largest amount of data (in bytes) allowed on stdout or
stderr - if exceeded child process is killed (Default: 200*1024)</li>
<li><code>killSignal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <span class="type"><Integer></span> (Default: 'SIGTERM')</li>
<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.)</li>
<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.)</li>
</ul>
</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> called with the output when process terminates<ul>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
<li><code>stdout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
<li><code>stderr</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
</ul>
</li>
<li>Returns: <a href="child_process.html#child_process_class_childprocess" class="type"><ChildProcess></a></li>
</ul>
<p>The <code>child_process.execFile()</code> function is similar to <a href="#child_process_child_process_exec_command_options_callback"><code>child_process.exec()</code></a>
except that it does not spawn a shell. Rather, the specified executable <code>file</code>
is spawned directly as a new process making it slightly more efficient than
<a href="#child_process_child_process_exec_command_options_callback"><code>child_process.exec()</code></a>.</p>
<p>The same options as <code>child_process.exec()</code> are supported. Since a shell is not
spawned, behaviors such as I/O redirection and file globbing are not supported.</p>
<pre><code class="lang-js">const execFile = require('child_process').execFile;
const child = execFile('node', ['--version'], (error, stdout, stderr) => {
if (error) {
throw error;
}
console.log(stdout);
});
</code></pre>
<p>The <code>stdout</code> and <code>stderr</code> arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The <code>encoding</code> option
can be used to specify the character encoding used to decode the stdout and
stderr output. If <code>encoding</code> is <code>'buffer'</code>, or an unrecognized character
encoding, <code>Buffer</code> objects will be passed to the callback instead.</p>
<h3>child_process.fork(modulePath[, args][, options])<span><a class="mark" href="#child_process_child_process_fork_modulepath_args_options" id="child_process_child_process_fork_modulepath_args_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><ul>
<li><code>modulePath</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The module to run in the child</li>
<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> List of string arguments</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>cwd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Current working directory of the child process</li>
<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Environment key-value pairs</li>
<li><code>execPath</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Executable used to create the child process</li>
<li><code>execArgv</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> List of string arguments passed to the executable
(Default: <code>process.execArgv</code>)</li>
<li><code>silent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> If true, stdin, stdout, and stderr of the child will be
piped to the parent, otherwise they will be inherited from the parent, see
the <code>'pipe'</code> and <code>'inherit'</code> options for <a href="#child_process_child_process_spawn_command_args_options"><code>child_process.spawn()</code></a>'s
<a href="#child_process_options_stdio"><code>stdio</code></a> for more details (default is false)</li>
<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.)</li>
<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.)</li>
</ul>
</li>
<li>Returns: <a href="child_process.html#child_process_class_childprocess" class="type"><ChildProcess></a></li>
</ul>
<p>The <code>child_process.fork()</code> method is a special case of
<a href="#child_process_child_process_spawn_command_args_options"><code>child_process.spawn()</code></a> used specifically to spawn new Node.js processes.
Like <code>child_process.spawn()</code>, a <code>ChildProcess</code> object is returned. The returned
<code>ChildProcess</code> will have an additional communication channel built-in that
allows messages to be passed back and forth between the parent and child. See
<a href="#child_process_child_send_message_sendhandle_callback"><code>ChildProcess#send()</code></a> for details.</p>
<p>It is important to keep in mind that spawned Node.js child processes are
independent of the parent with exception of the IPC communication channel
that is established between the two. Each process has its own memory, with
their own V8 instances. Because of the additional resource allocations
required, spawning a large number of child Node.js processes is not
recommended.</p>
<p>By default, <code>child_process.fork()</code> will spawn new Node.js instances using the
<code>process.execPath</code> of the parent process. The <code>execPath</code> property in the
<code>options</code> object allows for an alternative execution path to be used.</p>
<p>Node.js processes launched with a custom <code>execPath</code> will communicate with the
parent process using the file descriptor (fd) identified using the
environment variable <code>NODE_CHANNEL_FD</code> on the child process. The input and
output on this fd is expected to be line delimited JSON objects.</p>
<p><em>Note: Unlike the <code>fork()</code> POSIX system call, <a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a> does
not clone the current process.</em></p>
<h3>child_process.spawn(command[, args][, options])<span><a class="mark" href="#child_process_child_process_spawn_command_args_options" id="child_process_child_process_spawn_command_args_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><code>command</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The command to run</li>
<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> List of string arguments</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>cwd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Current working directory of the child process</li>
<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Environment key-value pairs</li>
<li><code>stdio</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Child's stdio configuration. (See
<a href="#child_process_options_stdio"><code>options.stdio</code></a>)</li>
<li><code>detached</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Prepare child to run independently of its parent
process. Specific behavior depends on the platform, see
<a href="#child_process_options_detached"><code>options.detached</code></a>)</li>
<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.)</li>
<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.)</li>
<li><code>shell</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> If <code>true</code>, runs <code>command</code> inside of a shell. Uses
'/bin/sh' on UNIX, and 'cmd.exe' on Windows. A different shell can be
specified as a string. The shell should understand the <code>-c</code> switch on UNIX,
or <code>/s /c</code> on Windows. Defaults to <code>false</code> (no shell).</li>
</ul>
</li>
<li>Returns: <a href="child_process.html#child_process_class_childprocess" class="type"><ChildProcess></a></li>
</ul>
<p>The <code>child_process.spawn()</code> method spawns a new process using the given
<code>command</code>, with command line arguments in <code>args</code>. If omitted, <code>args</code> defaults
to an empty array.</p>
<p><strong>Note: If the <code>shell</code> option is enabled, do not pass unsanitised user input to
this function. Any input containing shell metacharacters may be used to
trigger arbitrary command execution.</strong></p>
<p>A third argument may be used to specify additional options, with these defaults:</p>
<pre><code class="lang-js">{
cwd: undefined,
env: process.env
}
</code></pre>
<p>Use <code>cwd</code> to specify the working directory from which the process is spawned.
If not given, the default is to inherit the current working directory.</p>
<p>Use <code>env</code> to specify environment variables that will be visible to the new
process, the default is <code>process.env</code>.</p>
<p>Example of running <code>ls -lh /usr</code>, capturing <code>stdout</code>, <code>stderr</code>, and the
exit code:</p>
<pre><code class="lang-js">const spawn = require('child_process').spawn;
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
</code></pre>
<p>Example: A very elaborate way to run 'ps ax | grep ssh'</p>
<pre><code class="lang-js">const spawn = require('child_process').spawn;
const ps = spawn('ps', ['ax']);
const grep = spawn('grep', ['ssh']);
ps.stdout.on('data', (data) => {
grep.stdin.write(data);
});
ps.stderr.on('data', (data) => {
console.log(`ps stderr: ${data}`);
});
ps.on('close', (code) => {
if (code !== 0) {
console.log(`ps process exited with code ${code}`);
}
grep.stdin.end();
});
grep.stdout.on('data', (data) => {
console.log(`${data}`);
});
grep.stderr.on('data', (data) => {
console.log(`grep stderr: ${data}`);
});
grep.on('close', (code) => {
if (code !== 0) {
console.log(`grep process exited with code ${code}`);
}
});
</code></pre>
<p>Example of checking for failed exec:</p>
<pre><code class="lang-js">const spawn = require('child_process').spawn;
const child = spawn('bad_command');
child.on('error', (err) => {
console.log('Failed to start child process.');
});
</code></pre>
<h4>options.detached<span><a class="mark" href="#child_process_options_detached" id="child_process_options_detached">#</a></span></h4>
<div class="api_metadata">
<span>Added in: v0.7.10</span>
</div><p>On Windows, setting <code>options.detached</code> to <code>true</code> makes it possible for the
child process to continue running after the parent exits. The child will have
its own console window. <em>Once enabled for a child process, it cannot be
disabled</em>.</p>
<p>On non-Windows platforms, if <code>options.detached</code> is set to <code>true</code>, the child
process will be made the leader of a new process group and session. Note that
child processes may continue running after the parent exits regardless of
whether they are detached or not. See <code>setsid(2)</code> for more information.</p>
<p>By default, the parent will wait for the detached child to exit. To prevent
the parent from waiting for a given <code>child</code>, use the <code>child.unref()</code> method.
Doing so will cause the parent's event loop to not include the child in its
reference count, allowing the parent to exit independently of the child, unless
there is an established IPC channel between the child and parent.</p>
<p>When using the <code>detached</code> option to start a long-running process, the process
will not stay running in the background after the parent exits unless it is
provided with a <code>stdio</code> configuration that is not connected to the parent.
If the parent's <code>stdio</code> is inherited, the child will remain attached to the
controlling terminal.</p>
<p>Example of a long-running process, by detaching and also ignoring its parent
<code>stdio</code> file descriptors, in order to ignore the parent's termination:</p>
<pre><code class="lang-js">const spawn = require('child_process').spawn;
const child = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
child.unref();
</code></pre>
<p>Alternatively one can redirect the child process' output into files:</p>
<pre><code class="lang-js">const fs = require('fs');
const spawn = require('child_process').spawn;
const out = fs.openSync('./out.log', 'a');
const err = fs.openSync('./out.log', 'a');
const child = spawn('prg', [], {
detached: true,
stdio: [ 'ignore', out, err ]
});
child.unref();
</code></pre>
<h4>options.stdio<span><a class="mark" href="#child_process_options_stdio" id="child_process_options_stdio">#</a></span></h4>
<div class="api_metadata">
<span>Added in: v0.7.10</span>
</div><p>The <code>options.stdio</code> option is used to configure the pipes that are established
between the parent and child process. By default, the child's stdin, stdout,
and stderr are redirected to corresponding <code>child.stdin</code>, <code>child.stdout</code>, and
<code>child.stderr</code> streams on the <code>ChildProcess</code> object. This is equivalent to
setting the <code>options.stdio</code> equal to <code>['pipe', 'pipe', 'pipe']</code>.</p>
<p>For convenience, <code>options.stdio</code> may be one of the following strings:</p>
<ul>
<li><code>'pipe'</code> - equivalent to <code>['pipe', 'pipe', 'pipe']</code> (the default)</li>
<li><code>'ignore'</code> - equivalent to <code>['ignore', 'ignore', 'ignore']</code></li>
<li><code>'inherit'</code> - equivalent to <code>[process.stdin, process.stdout, process.stderr]</code>
or <code>[0,1,2]</code></li>
</ul>
<p>Otherwise, the value of <code>option.stdio</code> is an array where each index corresponds
to an fd in the child. The fds 0, 1, and 2 correspond to stdin, stdout,
and stderr, respectively. Additional fds can be specified to create additional
pipes between the parent and child. The value is one of the following:</p>
<ol>
<li><code>'pipe'</code> - Create a pipe between the child process and the parent process.
The parent end of the pipe is exposed to the parent as a property on the
<code>child_process</code> object as <code>ChildProcess.stdio[fd]</code>. Pipes created for
fds 0 - 2 are also available as ChildProcess.stdin, ChildProcess.stdout
and ChildProcess.stderr, respectively.</li>
<li><code>'ipc'</code> - Create an IPC channel for passing messages/file descriptors
between parent and child. A ChildProcess may have at most <em>one</em> IPC stdio
file descriptor. Setting this option enables the ChildProcess.send() method.
If the child writes JSON messages to this file descriptor, the
<code>ChildProcess.on('message')</code> event handler will be triggered in the parent.
If the child is a Node.js process, the presence of an IPC channel will enable
<code>process.send()</code>, <code>process.disconnect()</code>, <code>process.on('disconnect')</code>, and
<code>process.on('message')</code> within the child.</li>
<li><code>'ignore'</code> - Instructs Node.js to ignore the fd in the child. While Node.js
will always open fds 0 - 2 for the processes it spawns, setting the fd to
<code>'ignore'</code> will cause Node.js to open <code>/dev/null</code> and attach it to the
child's fd.</li>
<li><code>Stream</code> object - Share a readable or writable stream that refers to a tty,
file, socket, or a pipe with the child process. The stream's underlying
file descriptor is duplicated in the child process to the fd that
corresponds to the index in the <code>stdio</code> array. Note that the stream must
have an underlying descriptor (file streams do not until the <code>'open'</code>
event has occurred).</li>
<li>Positive integer - The integer value is interpreted as a file descriptor
that is is currently open in the parent process. It is shared with the child
process, similar to how <code>Stream</code> objects can be shared.</li>
<li><code>null</code>, <code>undefined</code> - Use default value. For stdio fds 0, 1 and 2 (in other
words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the
default is <code>'ignore'</code>.</li>
</ol>
<p>Example:</p>
<pre><code class="lang-js">const spawn = require('child_process').spawn;
// Child will use parent's stdios
spawn('prg', [], { stdio: 'inherit' });
// Spawn child sharing only stderr
spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });
// Open an extra fd=4, to interact with programs presenting a
// startd-style interface.
spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });
</code></pre>
<p><em>It is worth noting that when an IPC channel is established between the
parent and child processes, and the child is a Node.js process, the child
is launched with the IPC channel unreferenced (using <code>unref()</code>) until the
child registers an event handler for the <code>process.on('disconnect')</code> event
or the <code>process.on('message')</code> event.This allows the child to exit normally
without the process being held open by the open IPC channel.</em></p>
<p>See also: <a href="#child_process_child_process_exec_command_options_callback"><code>child_process.exec()</code></a> and <a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a></p>
<h2>Synchronous Process Creation<span><a class="mark" href="#child_process_synchronous_process_creation" id="child_process_synchronous_process_creation">#</a></span></h2>
<p>The <code>child_process.spawnSync()</code>, <code>child_process.execSync()</code>, and
<code>child_process.execFileSync()</code> methods are <strong>synchronous</strong> and <strong>WILL</strong> block
the Node.js event loop, pausing execution of any additional code until the
spawned process exits.</p>
<p>Blocking calls like these are mostly useful for simplifying general purpose
scripting tasks and for simplifying the loading/processing of application
configuration at startup.</p>
<h3>child_process.execFileSync(file[, args][, options])<span><a class="mark" href="#child_process_child_process_execfilesync_file_args_options" id="child_process_child_process_execfilesync_file_args_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The name or path of the executable file to run</li>
<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> List of string arguments</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>cwd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Current working directory of the child process</li>
<li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> The value which will be passed as stdin to the spawned process<ul>
<li>supplying this value will override <code>stdio[0]</code></li>
</ul>
</li>
<li><code>stdio</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> Child's stdio configuration. (Default: 'pipe')<ul>
<li><code>stderr</code> by default will be output to the parent process' stderr unless
<code>stdio</code> is specified</li>
</ul>
</li>
<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Environment key-value pairs</li>
<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.)</li>
<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.)</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)</li>
<li><code>killSignal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <span class="type"><Integer></span> The signal value to be used when the spawned process will be killed. (Default: 'SIGTERM')</li>
<li><code>maxBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> largest amount of data (in bytes) allowed on stdout or
stderr - if exceeded child process is killed</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The encoding used for all stdio inputs and outputs. (Default: 'buffer')</li>
</ul>
</li>
<li>Returns: <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The stdout from the command</li>
</ul>
<p>The <code>child_process.execFileSync()</code> method is generally identical to
<code>child_process.execFile()</code> with the exception that the method will not return
until the child process has fully closed. When a timeout has been encountered
and <code>killSignal</code> is sent, the method won't return until the process has
completely exited. <em>Note that if the child process intercepts and handles
the <code>SIGTERM</code> signal and does not exit, the parent process will still wait
until the child process has exited.</em></p>
<p>If the process times out, or has a non-zero exit code, this method <strong><em>will</em></strong>
throw. The <a href="errors.html#errors_class_error"><code>Error</code></a> object will contain the entire result from
<a href="#child_process_child_process_spawnsync_command_args_options"><code>child_process.spawnSync()</code></a></p>
<h3>child_process.execSync(command[, options])<span><a class="mark" href="#child_process_child_process_execsync_command_options" id="child_process_child_process_execsync_command_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><ul>
<li><code>command</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The command to run</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>cwd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Current working directory of the child process</li>
<li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> The value which will be passed as stdin to the spawned process<ul>
<li>supplying this value will override <code>stdio[0]</code></li>
</ul>
</li>
<li><code>stdio</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> Child's stdio configuration. (Default: 'pipe')<ul>
<li><code>stderr</code> by default will be output to the parent process' stderr unless
<code>stdio</code> is specified</li>
</ul>
</li>
<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Environment key-value pairs</li>
<li><code>shell</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Shell to execute the command with
(Default: '/bin/sh' on UNIX, 'cmd.exe' on Windows, The shell should
understand the <code>-c</code> switch on UNIX or <code>/s /c</code> on Windows. On Windows,
command line parsing should be compatible with <code>cmd.exe</code>.)</li>
<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.)</li>
<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.)</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)</li>
<li><code>killSignal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <span class="type"><Integer></span> The signal value to be used when the spawned process will be killed. (Default: 'SIGTERM')</li>
<li><code>maxBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> largest amount of data (in bytes) allowed on stdout or
stderr - if exceeded child process is killed</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The encoding used for all stdio inputs and outputs. (Default: 'buffer')</li>
</ul>
</li>
<li>Returns: <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The stdout from the command</li>
</ul>
<p>The <code>child_process.execSync()</code> method is generally identical to
<code>child_process.exec()</code> with the exception that the method will not return until
the child process has fully closed. When a timeout has been encountered and
<code>killSignal</code> is sent, the method won't return until the process has completely
exited. <em>Note that if the child process intercepts and handles the <code>SIGTERM</code>
signal and doesn't exit, the parent process will wait until the child
process has exited.</em></p>
<p>If the process times out, or has a non-zero exit code, this method <strong><em>will</em></strong>
throw. The <a href="errors.html#errors_class_error"><code>Error</code></a> object will contain the entire result from
<a href="#child_process_child_process_spawnsync_command_args_options"><code>child_process.spawnSync()</code></a></p>
<p><strong>Note: Never pass unsanitised user input to this function. Any input
containing shell metacharacters may be used to trigger arbitrary command
execution.</strong></p>
<h3>child_process.spawnSync(command[, args][, options])<span><a class="mark" href="#child_process_child_process_spawnsync_command_args_options" id="child_process_child_process_spawnsync_command_args_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><ul>
<li><code>command</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The command to run</li>
<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> List of string arguments</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>cwd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Current working directory of the child process</li>
<li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> The value which will be passed as stdin to the spawned process<ul>
<li>supplying this value will override <code>stdio[0]</code></li>
</ul>
</li>
<li><code>stdio</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> Child's stdio configuration. (Default: 'pipe')</li>
<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Environment key-value pairs</li>
<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.)</li>
<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.)</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)</li>
<li><code>killSignal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <span class="type"><Integer></span> The signal value to be used when the spawned process will be killed. (Default: 'SIGTERM')</li>
<li><code>maxBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> largest amount of data (in bytes) allowed on stdout or
stderr - if exceeded child process is killed</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The encoding used for all stdio inputs and outputs. (Default: 'buffer')</li>
<li><code>shell</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> If <code>true</code>, runs <code>command</code> inside of a shell. Uses
'/bin/sh' on UNIX, and 'cmd.exe' on Windows. A different shell can be
specified as a string. The shell should understand the <code>-c</code> switch on UNIX,
or <code>/s /c</code> on Windows. Defaults to <code>false</code> (no shell).</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>pid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Pid of the child process</li>
<li><code>output</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> Array of results from stdio output</li>
<li><code>stdout</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The contents of <code>output[1]</code></li>
<li><code>stderr</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The contents of <code>output[2]</code></li>
<li><code>status</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The exit code of the child process</li>
<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The signal used to kill the child process</li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a> The error object if the child process failed or timed out</li>
</ul>
</li>
</ul>
<p>The <code>child_process.spawnSync()</code> method is generally identical to
<code>child_process.spawn()</code> with the exception that the function will not return
until the child process has fully closed. When a timeout has been encountered
and <code>killSignal</code> is sent, the method won't return until the process has
completely exited. Note that if the process intercepts and handles the
<code>SIGTERM</code> signal and doesn't exit, the parent process will wait until the child
process has exited.</p>
<p><strong>Note: If the <code>shell</code> option is enabled, do not pass unsanitised user input to
this function. Any input containing shell metacharacters may be used to
trigger arbitrary command execution.</strong></p>
<h2>Class: ChildProcess<span><a class="mark" href="#child_process_class_childprocess" id="child_process_class_childprocess">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v2.2.0</span>
</div><p>Instances of the <code>ChildProcess</code> class are <a href="events.html#events_class_events_eventemitter"><code>EventEmitters</code></a> that represent
spawned child processes.</p>
<p>Instances of <code>ChildProcess</code> are not intended to be created directly. Rather,
use the <a href="#child_process_child_process_spawn_command_args_options"><code>child_process.spawn()</code></a>, <a href="#child_process_child_process_exec_command_options_callback"><code>child_process.exec()</code></a>,
<a href="#child_process_child_process_execfile_file_args_options_callback"><code>child_process.execFile()</code></a>, or <a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a> methods to create
instances of <code>ChildProcess</code>.</p>
<h3>Event: 'close'<span><a class="mark" href="#child_process_event_close" id="child_process_event_close">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><ul>
<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> the exit code if the child exited on its own.</li>
<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> the signal by which the child process was terminated.</li>
</ul>
<p>The <code>'close'</code> event is emitted when the stdio streams of a child process have
been closed. This is distinct from the <code>'exit'</code> event, since multiple
processes might share the same stdio streams.</p>
<h3>Event: 'disconnect'<span><a class="mark" href="#child_process_event_disconnect" id="child_process_event_disconnect">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.2</span>
</div><p>The <code>'disconnect'</code> event is emitted after calling the
<code>ChildProcess.disconnect()</code> method in the parent or child process. After
disconnecting it is no longer possible to send or receive messages, and the
<code>ChildProcess.connected</code> property is false.</p>
<h3>Event: 'error'<span><a class="mark" href="#child_process_event_error" id="child_process_event_error">#</a></span></h3>
<div class="signature"><ul>
<li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a> the error.</li>
</ul>
</div><p>The <code>'error'</code> event is emitted whenever:</p>
<ol>
<li>The process could not be spawned, or</li>
<li>The process could not be killed, or</li>
<li>Sending a message to the child process failed.</li>
</ol>
<p>Note that the <code>'exit'</code> event may or may not fire after an error has occurred.
If you are listening to both the <code>'exit'</code> and <code>'error'</code> events, it is important
to guard against accidentally invoking handler functions multiple times.</p>
<p>See also <a href="#child_process_child_kill_signal"><code>ChildProcess#kill()</code></a> and <a href="#child_process_child_send_message_sendhandle_callback"><code>ChildProcess#send()</code></a>.</p>
<h3>Event: 'exit'<span><a class="mark" href="#child_process_event_exit" id="child_process_event_exit">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> the exit code if the child exited on its own.</li>
<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> the signal by which the child process was terminated.</li>
</ul>
<p>The <code>'exit'</code> event is emitted after the child process ends. If the process
exited, <code>code</code> is the final exit code of the process, otherwise <code>null</code>. If the
process terminated due to receipt of a signal, <code>signal</code> is the string name of
the signal, otherwise <code>null</code>. One of the two will always be non-null.</p>
<p>Note that when the <code>'exit'</code> event is triggered, child process stdio streams
might still be open.</p>
<p>Also, note that Node.js establishes signal handlers for <code>SIGINT</code> and
<code>SIGTERM</code> and Node.js processes will not terminate immediately due to receipt
of those signals. Rather, Node.js will perform a sequence of cleanup actions
and then will re-raise the handled signal.</p>
<p>See <code>waitpid(2)</code>.</p>
<h3>Event: 'message'<span><a class="mark" href="#child_process_event_message" id="child_process_event_message">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> a parsed JSON object or primitive value.</li>
<li><code>sendHandle</code> <a href="net.html#net_server_listen_handle_backlog_callback" class="type"><Handle></a> a <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> or <a href="net.html#net_class_net_server"><code>net.Server</code></a> object, or
undefined.</li>
</ul>
<p>The <code>'message'</code> event is triggered when a child process uses <code>process.send()</code>
to send messages.</p>
<h3>child.connected<span><a class="mark" href="#child_process_child_connected" id="child_process_child_connected">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.2</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Set to false after <code>.disconnect</code> is called</li>
</ul>
<p>The <code>child.connected</code> property indicates whether it is still possible to send
and receive messages from a child process. When <code>child.connected</code> is false, it
is no longer possible to send or receive messages.</p>
<h3>child.disconnect()<span><a class="mark" href="#child_process_child_disconnect" id="child_process_child_disconnect">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.2</span>
</div><p>Closes the IPC channel between parent and child, allowing the child to exit
gracefully once there are no other connections keeping it alive. After calling
this method the <code>child.connected</code> and <code>process.connected</code> properties in both
the parent and child (respectively) will be set to <code>false</code>, and it will be no
longer possible to pass messages between the processes.</p>
<p>The <code>'disconnect'</code> event will be emitted when there are no messages in the
process of being received. This will most often be triggered immediately after
calling <code>child.disconnect()</code>.</p>
<p>Note that when the child process is a Node.js instance (e.g. spawned using
<a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a>), the <code>process.disconnect()</code> method can be invoked
within the child process to close the IPC channel as well.</p>
<h3>child.kill([signal])<span><a class="mark" href="#child_process_child_kill_signal" id="child_process_child_kill_signal">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
<p>The <code>child.kill()</code> methods sends a signal to the child process. If no argument
is given, the process will be sent the <code>'SIGTERM'</code> signal. See <a href="http://man7.org/linux/man-pages/man7/signal.7.html">signal(7)</a> for
a list of available signals.</p>
<pre><code class="lang-js">const spawn = require('child_process').spawn;
const grep = spawn('grep', ['ssh']);
grep.on('close', (code, signal) => {
console.log(
`child process terminated due to receipt of signal ${signal}`);
});
// Send SIGHUP to process
grep.kill('SIGHUP');
</code></pre>
<p>The <code>ChildProcess</code> object may emit an <code>'error'</code> event if the signal cannot be
delivered. Sending a signal to a child process that has already exited is not
an error but may have unforeseen consequences. Specifically, if the process
identifier (PID) has been reassigned to another process, the signal will be
delivered to that process instead which can have unexpected results.</p>
<p>Note that while the function is called <code>kill</code>, the signal delivered to the
child process may not actually terminate the process.</p>
<p>See <code>kill(2)</code> for reference.</p>
<p>Also note: on Linux, child processes of child processes will not be terminated
when attempting to kill their parent. This is likely to happen when running a
new process in a shell or with use of the <code>shell</code> option of <code>ChildProcess</code>, such
as in this example:</p>
<pre><code class="lang-js">'use strict';
const spawn = require('child_process').spawn;
let child = spawn('sh', ['-c',
`node -e "setInterval(() => {
console.log(process.pid, 'is alive')
}, 500);"`
], {
stdio: ['inherit', 'inherit', 'inherit']
});
setTimeout(() => {
child.kill(); // does not terminate the node process in the shell
}, 2000);
</code></pre>
<h3>child.pid<span><a class="mark" href="#child_process_child_pid" id="child_process_child_pid">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Integer</li>
</ul>
<p>Returns the process identifier (PID) of the child process.</p>
<p>Example:</p>
<pre><code class="lang-js">const spawn = require('child_process').spawn;
const grep = spawn('grep', ['ssh']);
console.log(`Spawned child pid: ${grep.pid}`);
grep.stdin.end();
</code></pre>
<h3>child.send(message[, sendHandle][, callback])<span><a class="mark" href="#child_process_child_send_message_sendhandle_callback" id="child_process_child_send_message_sendhandle_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>sendHandle</code> <a href="net.html#net_server_listen_handle_backlog_callback" class="type"><Handle></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>When an IPC channel has been established between the parent and child (
i.e. when using <a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a>), the <code>child.send()</code> method can be
used to send messages to the child process. When the child process is a Node.js
instance, these messages can be received via the <code>process.on('message')</code> event.</p>
<p>For example, in the parent script:</p>
<pre><code class="lang-js">const cp = require('child_process');
const n = cp.fork(`${__dirname}/sub.js`);
n.on('message', (m) => {
console.log('PARENT got message:', m);
});
n.send({ hello: 'world' });
</code></pre>
<p>And then the child script, <code>'sub.js'</code> might look like this:</p>
<pre><code class="lang-js">process.on('message', (m) => {
console.log('CHILD got message:', m);
});
process.send({ foo: 'bar' });
</code></pre>
<p>Child Node.js processes will have a <code>process.send()</code> method of their own that
allows the child to send messages back to the parent.</p>
<p>There is a special case when sending a <code>{cmd: 'NODE_foo'}</code> message. All messages
containing a <code>NODE_</code> prefix in its <code>cmd</code> property are considered to be reserved
for use within Node.js core and will not be emitted in the child's
<code>process.on('message')</code> event. Rather, such messages are emitted using the
<code>process.on('internalMessage')</code> event and are consumed internally by Node.js.
Applications should avoid using such messages or listening for
<code>'internalMessage'</code> events as it is subject to change without notice.</p>
<p>The optional <code>sendHandle</code> argument that may be passed to <code>child.send()</code> is for
passing a TCP server or socket object to the child process. The child will
receive the object as the second argument passed to the callback function
registered on the <code>process.on('message')</code> event. Any data that is received and
buffered in the socket will not be sent to the child.</p>
<p>The optional <code>callback</code> is a function that is invoked after the message is
sent but before the child may have received it. The function is called with a
single argument: <code>null</code> on success, or an <a href="errors.html#errors_class_error"><code>Error</code></a> object on failure.</p>
<p>If no <code>callback</code> function is provided and the message cannot be sent, an
<code>'error'</code> event will be emitted by the <code>ChildProcess</code> object. This can happen,
for instance, when the child process has already exited.</p>
<p><code>child.send()</code> will return <code>false</code> if the channel has closed or when the
backlog of unsent messages exceeds a threshold that makes it unwise to send
more. Otherwise, the method returns <code>true</code>. The <code>callback</code> function can be
used to implement flow control.</p>
<h4>Example: sending a server object<span><a class="mark" href="#child_process_example_sending_a_server_object" id="child_process_example_sending_a_server_object">#</a></span></h4>
<p>The <code>sendHandle</code> argument can be used, for instance, to pass the handle of
a TCP server object to the child process as illustrated in the example below:</p>
<pre><code class="lang-js">const child = require('child_process').fork('child.js');
// Open up the server object and send the handle.
const server = require('net').createServer();
server.on('connection', (socket) => {
socket.end('handled by parent');
});
server.listen(1337, () => {
child.send('server', server);
});
</code></pre>
<p>The child would then receive the server object as:</p>
<pre><code class="lang-js">process.on('message', (m, server) => {
if (m === 'server') {
server.on('connection', (socket) => {
socket.end('handled by child');
});
}
});
</code></pre>
<p>Once the server is now shared between the parent and child, some connections
can be handled by the parent and some by the child.</p>
<p>While the example above uses a server created using the <code>net</code> module, <code>dgram</code>
module servers use exactly the same workflow with the exceptions of listening on
a <code>'message'</code> event instead of <code>'connection'</code> and using <code>server.bind</code> instead of
<code>server.listen</code>. This is, however, currently only supported on UNIX platforms.</p>
<h4>Example: sending a socket object<span><a class="mark" href="#child_process_example_sending_a_socket_object" id="child_process_example_sending_a_socket_object">#</a></span></h4>
<p>Similarly, the <code>sendHandler</code> argument can be used to pass the handle of a
socket to the child process. The example below spawns two children that each
handle connections with "normal" or "special" priority:</p>
<pre><code class="lang-js">const normal = require('child_process').fork('child.js', ['normal']);
const special = require('child_process').fork('child.js', ['special']);
// Open up the server and send sockets to child
const server = require('net').createServer();
server.on('connection', (socket) => {
// If this is special priority
if (socket.remoteAddress === '74.125.127.100') {
special.send('socket', socket);
return;
}
// This is normal priority
normal.send('socket', socket);
});
server.listen(1337);
</code></pre>
<p>The <code>child.js</code> would receive the socket handle as the second argument passed
to the event callback function:</p>
<pre><code class="lang-js">process.on('message', (m, socket) => {
if (m === 'socket') {
socket.end(`Request handled with ${process.argv[2]} priority`);
}
});
</code></pre>
<p>Once a socket has been passed to a child, the parent is no longer capable of
tracking when the socket is destroyed. To indicate this, the <code>.connections</code>
property becomes <code>null</code>. It is recommended not to use <code>.maxConnections</code> when
this occurs.</p>
<p><em>Note: this function uses <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify"><code>JSON.stringify()</code></a> internally to serialize the <code>message</code>.</em></p>
<h3>child.stderr<span><a class="mark" href="#child_process_child_stderr" id="child_process_child_stderr">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><a href="stream.html#stream_stream" class="type"><Stream></a></li>
</ul>
<p>A <code>Readable Stream</code> that represents the child process's <code>stderr</code>.</p>
<p>If the child was spawned with <code>stdio[2]</code> set to anything other than <code>'pipe'</code>,
then this will be <code>undefined</code>.</p>
<p><code>child.stderr</code> is an alias for <code>child.stdio[2]</code>. Both properties will refer to
the same value.</p>
<h3>child.stdin<span><a class="mark" href="#child_process_child_stdin" id="child_process_child_stdin">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><a href="stream.html#stream_stream" class="type"><Stream></a></li>
</ul>
<p>A <code>Writable Stream</code> that represents the child process's <code>stdin</code>.</p>
<p><em>Note that if a child process waits to read all of its input, the child will not
continue until this stream has been closed via <code>end()</code>.</em></p>
<p>If the child was spawned with <code>stdio[0]</code> set to anything other than <code>'pipe'</code>,
then this will be <code>undefined</code>.</p>
<p><code>child.stdin</code> is an alias for <code>child.stdio[0]</code>. Both properties will refer to
the same value.</p>
<h3>child.stdio<span><a class="mark" href="#child_process_child_stdio" id="child_process_child_stdio">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.10</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a></li>
</ul>
<p>A sparse array of pipes to the child process, corresponding with positions in
the <a href="#child_process_options_stdio"><code>stdio</code></a> option passed to <a href="#child_process_child_process_spawn_command_args_options"><code>child_process.spawn()</code></a> that have been set
to the value <code>'pipe'</code>. Note that <code>child.stdio[0]</code>, <code>child.stdio[1]</code>, and
<code>child.stdio[2]</code> are also available as <code>child.stdin</code>, <code>child.stdout</code>, and
<code>child.stderr</code>, respectively.</p>
<p>In the following example, only the child's fd <code>1</code> (stdout) is configured as a
pipe, so only the parent's <code>child.stdio[1]</code> is a stream, all other values in
the array are <code>null</code>.</p>
<pre><code class="lang-js">const assert = require('assert');
const fs = require('fs');
const child_process = require('child_process');
const child = child_process.spawn('ls', {
stdio: [
0, // Use parents stdin for child
'pipe', // Pipe child's stdout to parent
fs.openSync('err.out', 'w') // Direct child's stderr to a file
]
});
assert.equal(child.stdio[0], null);
assert.equal(child.stdio[0], child.stdin);
assert(child.stdout);
assert.equal(child.stdio[1], child.stdout);
assert.equal(child.stdio[2], null);
assert.equal(child.stdio[2], child.stderr);
</code></pre>
<h3>child.stdout<span><a class="mark" href="#child_process_child_stdout" id="child_process_child_stdout">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><a href="stream.html#stream_stream" class="type"><Stream></a></li>
</ul>
<p>A <code>Readable Stream</code> that represents the child process's <code>stdout</code>.</p>
<p>If the child was spawned with <code>stdio[1]</code> set to anything other than <code>'pipe'</code>,
then this will be <code>undefined</code>.</p>
<p><code>child.stdout</code> is an alias for <code>child.stdio[1]</code>. Both properties will refer
to the same value.</p>
<!-- [end-include:child_process.md] -->
<!-- [start-include:cluster.md] -->
<h1>Cluster<span><a class="mark" href="#cluster_cluster" id="cluster_cluster">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>A single instance of Node.js runs in a single thread. To take advantage of
multi-core systems the user will sometimes want to launch a cluster of Node.js
processes to handle the load.</p>
<p>The cluster module allows you to easily create child processes that
all share server ports.</p>
<pre><code class="lang-js">const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
// Fork workers.
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`worker ${worker.process.pid} died`);
});
} else {
// Workers can share any TCP connection
// In this case it is an HTTP server
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
}
</code></pre>
<p>Running Node.js will now share port 8000 between the workers:</p>
<pre><code>$ NODE_DEBUG=cluster node server.js
23521,Master Worker 23524 online
23521,Master Worker 23526 online
23521,Master Worker 23523 online
23521,Master Worker 23528 online
</code></pre><p>Please note that, on Windows, it is not yet possible to set up a named pipe
server in a worker.</p>
<h2>How It Works<span><a class="mark" href="#cluster_how_it_works" id="cluster_how_it_works">#</a></span></h2>
<!--type=misc-->
<p>The worker processes are spawned using the <a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a> method,
so that they can communicate with the parent via IPC and pass server
handles back and forth.</p>
<p>The cluster module supports two methods of distributing incoming
connections.</p>
<p>The first one (and the default one on all platforms except Windows),
is the round-robin approach, where the master process listens on a
port, accepts new connections and distributes them across the workers
in a round-robin fashion, with some built-in smarts to avoid
overloading a worker process.</p>
<p>The second approach is where the master process creates the listen
socket and sends it to interested workers. The workers then accept
incoming connections directly.</p>
<p>The second approach should, in theory, give the best performance.
In practice however, distribution tends to be very unbalanced due
to operating system scheduler vagaries. Loads have been observed
where over 70% of all connections ended up in just two processes,
out of a total of eight.</p>
<p>Because <code>server.listen()</code> hands off most of the work to the master
process, there are three cases where the behavior between a normal
Node.js process and a cluster worker differs:</p>
<ol>
<li><code>server.listen({fd: 7})</code> Because the message is passed to the master,
file descriptor 7 <strong>in the parent</strong> will be listened on, and the
handle passed to the worker, rather than listening to the worker's
idea of what the number 7 file descriptor references.</li>
<li><code>server.listen(handle)</code> Listening on handles explicitly will cause
the worker to use the supplied handle, rather than talk to the master
process. If the worker already has the handle, then it's presumed
that you know what you are doing.</li>
<li><code>server.listen(0)</code> Normally, this will cause servers to listen on a
random port. However, in a cluster, each worker will receive the
same "random" port each time they do <code>listen(0)</code>. In essence, the
port is random the first time, but predictable thereafter. If you
want to listen on a unique port, generate a port number based on the
cluster worker ID.</li>
</ol>
<p>There is no routing logic in Node.js, or in your program, and no shared
state between the workers. Therefore, it is important to design your
program such that it does not rely too heavily on in-memory data objects
for things like sessions and login.</p>
<p>Because workers are all separate processes, they can be killed or
re-spawned depending on your program's needs, without affecting other
workers. As long as there are some workers still alive, the server will
continue to accept connections. If no workers are alive, existing connections
will be dropped and new connections will be refused. Node.js does not
automatically manage the number of workers for you, however. It is your
responsibility to manage the worker pool for your application's needs.</p>
<h2>Class: Worker<span><a class="mark" href="#cluster_class_worker" id="cluster_class_worker">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p>A Worker object contains all public information and method about a worker.
In the master it can be obtained using <code>cluster.workers</code>. In a worker
it can be obtained using <code>cluster.worker</code>.</p>
<h3>Event: 'disconnect'<span><a class="mark" href="#cluster_event_disconnect" id="cluster_event_disconnect">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>Similar to the <code>cluster.on('disconnect')</code> event, but specific to this worker.</p>
<pre><code class="lang-js">cluster.fork().on('disconnect', () => {
// Worker has disconnected
});
</code></pre>
<h3>Event: 'error'<span><a class="mark" href="#cluster_event_error" id="cluster_event_error">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.3</span>
</div><p>This event is the same as the one provided by <a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a>.</p>
<p>In a worker you can also use <code>process.on('error')</code>.</p>
<h3>Event: 'exit'<span><a class="mark" href="#cluster_event_exit" id="cluster_event_exit">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.2</span>
</div><ul>
<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> the exit code, if it exited normally.</li>
<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> the name of the signal (e.g. <code>'SIGHUP'</code>) that caused
the process to be killed.</li>
</ul>
<p>Similar to the <code>cluster.on('exit')</code> event, but specific to this worker.</p>
<pre><code class="lang-js">const worker = cluster.fork();
worker.on('exit', (code, signal) => {
if (signal) {
console.log(`worker was killed by signal: ${signal}`);
} else if (code !== 0) {
console.log(`worker exited with error code: ${code}`);
} else {
console.log('worker success!');
}
});
</code></pre>
<h3>Event: 'listening'<span><a class="mark" href="#cluster_event_listening" id="cluster_event_listening">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Similar to the <code>cluster.on('listening')</code> event, but specific to this worker.</p>
<pre><code class="lang-js">cluster.fork().on('listening', (address) => {
// Worker is listening
});
</code></pre>
<p>It is not emitted in the worker.</p>
<h3>Event: 'message'<span><a class="mark" href="#cluster_event_message" id="cluster_event_message">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>handle</code> <span class="type"><undefined></span> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Similar to the <code>cluster.on('message')</code> event, but specific to this worker. In a
worker you can also use <code>process.on('message')</code>.</p>
<p>See <a href="process.html#process_event_message"><code>process</code> event: <code>'message'</code></a>.</p>
<p>As an example, here is a cluster that keeps count of the number of requests
in the master process using the message system:</p>
<pre><code class="lang-js">const cluster = require('cluster');
const http = require('http');
if (cluster.isMaster) {
// Keep track of http requests
var numReqs = 0;
setInterval(() => {
console.log('numReqs =', numReqs);
}, 1000);
// Count requests
function messageHandler(msg) {
if (msg.cmd && msg.cmd == 'notifyRequest') {
numReqs += 1;
}
}
// Start workers and listen for messages containing notifyRequest
const numCPUs = require('os').cpus().length;
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
Object.keys(cluster.workers).forEach((id) => {
cluster.workers[id].on('message', messageHandler);
});
} else {
// Worker processes have a http server.
http.Server((req, res) => {
res.writeHead(200);
res.end('hello world\n');
// notify master about the request
process.send({ cmd: 'notifyRequest' });
}).listen(8000);
}
</code></pre>
<h3>Event: 'online'<span><a class="mark" href="#cluster_event_online" id="cluster_event_online">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p>Similar to the <code>cluster.on('online')</code> event, but specific to this worker.</p>
<pre><code class="lang-js">cluster.fork().on('online', () => {
// Worker is online
});
</code></pre>
<p>It is not emitted in the worker.</p>
<h3>worker.disconnect()<span><a class="mark" href="#cluster_worker_disconnect" id="cluster_worker_disconnect">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>In a worker, this function will close all servers, wait for the <code>'close'</code> event on
those servers, and then disconnect the IPC channel.</p>
<p>In the master, an internal message is sent to the worker causing it to call
<code>.disconnect()</code> on itself.</p>
<p>Causes <code>.suicide</code> to be set.</p>
<p>Note that after a server is closed, it will no longer accept new connections,
but connections may be accepted by any other listening worker. Existing
connections will be allowed to close as usual. When no more connections exist,
see <a href="#net_server_close_callback"><code>server.close()</code></a>, the IPC channel to the worker will close allowing it to
die gracefully.</p>
<p>The above applies <em>only</em> to server connections, client connections are not
automatically closed by workers, and disconnect does not wait for them to close
before exiting.</p>
<p>Note that in a worker, <code>process.disconnect</code> exists, but it is not this function,
it is <a href="child_process.html#child_process_child_disconnect"><code>disconnect</code></a>.</p>
<p>Because long living server connections may block workers from disconnecting, it
may be useful to send a message, so application specific actions may be taken to
close them. It also may be useful to implement a timeout, killing a worker if
the <code>'disconnect'</code> event has not been emitted after some time.</p>
<pre><code class="lang-js">if (cluster.isMaster) {
var worker = cluster.fork();
var timeout;
worker.on('listening', (address) => {
worker.send('shutdown');
worker.disconnect();
timeout = setTimeout(() => {
worker.kill();
}, 2000);
});
worker.on('disconnect', () => {
clearTimeout(timeout);
});
} else if (cluster.isWorker) {
const net = require('net');
var server = net.createServer((socket) => {
// connections never end
});
server.listen(8000);
process.on('message', (msg) => {
if (msg === 'shutdown') {
// initiate graceful close of any connections to server
}
});
}
</code></pre>
<h3>worker.id<span><a class="mark" href="#cluster_worker_id" id="cluster_worker_id">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.8.0</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
<p>Each new worker is given its own unique id, this id is stored in the
<code>id</code>.</p>
<p>While a worker is alive, this is the key that indexes it in
cluster.workers</p>
<h3>worker.isConnected()<span><a class="mark" href="#cluster_worker_isconnected" id="cluster_worker_isconnected">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>This function returns <code>true</code> if the worker is connected to its master via its IPC
channel, <code>false</code> otherwise. A worker is connected to its master after it's been
created. It is disconnected after the <code>'disconnect'</code> event is emitted.</p>
<h3>worker.isDead()<span><a class="mark" href="#cluster_worker_isdead" id="cluster_worker_isdead">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>This function returns <code>true</code> if the worker's process has terminated (either
because of exiting or being signaled). Otherwise, it returns <code>false</code>.</p>
<h3>worker.kill([signal='SIGTERM'])<span><a class="mark" href="#cluster_worker_kill_signal_sigterm" id="cluster_worker_kill_signal_sigterm">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.12</span>
</div><ul>
<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Name of the kill signal to send to the worker
process.</li>
</ul>
<p>This function will kill the worker. In the master, it does this by disconnecting
the <code>worker.process</code>, and once disconnected, killing with <code>signal</code>. In the
worker, it does it by disconnecting the channel, and then exiting with code <code>0</code>.</p>
<p>Causes <code>.suicide</code> to be set.</p>
<p>This method is aliased as <code>worker.destroy()</code> for backwards compatibility.</p>
<p>Note that in a worker, <code>process.kill()</code> exists, but it is not this function,
it is <a href="process.html#process_process_kill_pid_signal"><code>kill</code></a>.</p>
<h3>worker.process<span><a class="mark" href="#cluster_worker_process" id="cluster_worker_process">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><a href="child_process.html#child_process_class_childprocess" class="type"><ChildProcess></a></li>
</ul>
<p>All workers are created using <a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a>, the returned object
from this function is stored as <code>.process</code>. In a worker, the global <code>process</code>
is stored.</p>
<p>See: <a href="child_process.html#child_process_child_process_fork_modulepath_args_options">Child Process module</a></p>
<p>Note that workers will call <code>process.exit(0)</code> if the <code>'disconnect'</code> event occurs
on <code>process</code> and <code>.suicide</code> is not <code>true</code>. This protects against accidental
disconnection.</p>
<h3>worker.send(message[, sendHandle][, callback])<span><a class="mark" href="#cluster_worker_send_message_sendhandle_callback" id="cluster_worker_send_message_sendhandle_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>sendHandle</code> <a href="net.html#net_server_listen_handle_backlog_callback" class="type"><Handle></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li>Returns: Boolean</li>
</ul>
<p>Send a message to a worker or master, optionally with a handle.</p>
<p>In the master this sends a message to a specific worker. It is identical to
<a href="child_process.html#child_process_child_send_message_sendhandle_callback"><code>ChildProcess.send()</code></a>.</p>
<p>In a worker this sends a message to the master. It is identical to
<code>process.send()</code>.</p>
<p>This example will echo back all messages from the master:</p>
<pre><code class="lang-js">if (cluster.isMaster) {
var worker = cluster.fork();
worker.send('hi there');
} else if (cluster.isWorker) {
process.on('message', (msg) => {
process.send(msg);
});
}
</code></pre>
<h3>worker.suicide<span><a class="mark" href="#cluster_worker_suicide" id="cluster_worker_suicide">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
<span>Deprecated since: v6.0.0 </span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>Set by calling <code>.kill()</code> or <code>.disconnect()</code>, until then it is <code>undefined</code>.</p>
<p>The boolean <code>worker.suicide</code> lets you distinguish between voluntary and accidental
exit, the master may choose not to respawn a worker based on this value.</p>
<pre><code class="lang-js">cluster.on('exit', (worker, code, signal) => {
if (worker.suicide === true) {
console.log('Oh, it was just suicide\' – no need to worry').
}
});
// kill worker
worker.kill();
</code></pre>
<h2>Event: 'disconnect'<span><a class="mark" href="#cluster_event_disconnect_1" id="cluster_event_disconnect_1">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.9</span>
</div><ul>
<li><code>worker</code> <a href="cluster.html#cluster_class_worker" class="type"><cluster.Worker></a></li>
</ul>
<p>Emitted after the worker IPC channel has disconnected. This can occur when a
worker exits gracefully, is killed, or is disconnected manually (such as with
worker.disconnect()).</p>
<p>There may be a delay between the <code>'disconnect'</code> and <code>'exit'</code> events. These events
can be used to detect if the process is stuck in a cleanup or if there are
long-living connections.</p>
<pre><code class="lang-js">cluster.on('disconnect', (worker) => {
console.log(`The worker #${worker.id} has disconnected`);
});
</code></pre>
<h2>Event: 'exit'<span><a class="mark" href="#cluster_event_exit_1" id="cluster_event_exit_1">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.9</span>
</div><ul>
<li><code>worker</code> <a href="cluster.html#cluster_class_worker" class="type"><cluster.Worker></a></li>
<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> the exit code, if it exited normally.</li>
<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> the name of the signal (e.g. <code>'SIGHUP'</code>) that caused
the process to be killed.</li>
</ul>
<p>When any of the workers die the cluster module will emit the <code>'exit'</code> event.</p>
<p>This can be used to restart the worker by calling <code>.fork()</code> again.</p>
<pre><code class="lang-js">cluster.on('exit', (worker, code, signal) => {
console.log('worker %d died (%s). restarting...',
worker.process.pid, signal || code);
cluster.fork();
});
</code></pre>
<p>See <a href="child_process.html#child_process_event_exit">child_process event: 'exit'</a>.</p>
<h2>Event: 'fork'<span><a class="mark" href="#cluster_event_fork" id="cluster_event_fork">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><code>worker</code> <a href="cluster.html#cluster_class_worker" class="type"><cluster.Worker></a></li>
</ul>
<p>When a new worker is forked the cluster module will emit a <code>'fork'</code> event.
This can be used to log worker activity, and create your own timeout.</p>
<pre><code class="lang-js">var timeouts = [];
function errorMsg() {
console.error('Something must be wrong with the connection ...');
}
cluster.on('fork', (worker) => {
timeouts[worker.id] = setTimeout(errorMsg, 2000);
});
cluster.on('listening', (worker, address) => {
clearTimeout(timeouts[worker.id]);
});
cluster.on('exit', (worker, code, signal) => {
clearTimeout(timeouts[worker.id]);
errorMsg();
});
</code></pre>
<h2>Event: 'listening'<span><a class="mark" href="#cluster_event_listening_1" id="cluster_event_listening_1">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><code>worker</code> <a href="cluster.html#cluster_class_worker" class="type"><cluster.Worker></a></li>
<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>After calling <code>listen()</code> from a worker, when the <code>'listening'</code> event is emitted on
the server, a <code>'listening'</code> event will also be emitted on <code>cluster</code> in the master.</p>
<p>The event handler is executed with two arguments, the <code>worker</code> contains the worker
object and the <code>address</code> object contains the following connection properties:
<code>address</code>, <code>port</code> and <code>addressType</code>. This is very useful if the worker is listening
on more than one address.</p>
<pre><code class="lang-js">cluster.on('listening', (worker, address) => {
console.log(
`A worker is now connected to ${address.address}:${address.port}`);
});
</code></pre>
<p>The <code>addressType</code> is one of:</p>
<ul>
<li><code>4</code> (TCPv4)</li>
<li><code>6</code> (TCPv6)</li>
<li><code>-1</code> (unix domain socket)</li>
<li><code>"udp4"</code> or <code>"udp6"</code> (UDP v4 or v6)</li>
</ul>
<h2>Event: 'message'<span><a class="mark" href="#cluster_event_message_1" id="cluster_event_message_1">#</a></span></h2>
<div class="signature"><ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>handle</code> <span class="type"><undefined></span> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
</div><p>Emitted when the cluster master receives a message from any worker.</p>
<p>See <a href="child_process.html#child_process_event_message">child_process event: 'message'</a>.</p>
<h2>Event: 'online'<span><a class="mark" href="#cluster_event_online_1" id="cluster_event_online_1">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><code>worker</code> <a href="cluster.html#cluster_class_worker" class="type"><cluster.Worker></a></li>
</ul>
<p>After forking a new worker, the worker should respond with an online message.
When the master receives an online message it will emit this event.
The difference between <code>'fork'</code> and <code>'online'</code> is that fork is emitted when the
master forks a worker, and 'online' is emitted when the worker is running.</p>
<pre><code class="lang-js">cluster.on('online', (worker) => {
console.log('Yay, the worker responded after it was forked');
});
</code></pre>
<h2>Event: 'setup'<span><a class="mark" href="#cluster_event_setup" id="cluster_event_setup">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.1</span>
</div><ul>
<li><code>settings</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Emitted every time <code>.setupMaster()</code> is called.</p>
<p>The <code>settings</code> object is the <code>cluster.settings</code> object at the time
<code>.setupMaster()</code> was called and is advisory only, since multiple calls to
<code>.setupMaster()</code> can be made in a single tick.</p>
<p>If accuracy is important, use <code>cluster.settings</code>.</p>
<h2>cluster.disconnect([callback])<span><a class="mark" href="#cluster_cluster_disconnect_callback" id="cluster_cluster_disconnect_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><ul>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> called when all workers are disconnected and handles are
closed</li>
</ul>
<p>Calls <code>.disconnect()</code> on each worker in <code>cluster.workers</code>.</p>
<p>When they are disconnected all internal handles will be closed, allowing the
master process to die gracefully if no other event is waiting.</p>
<p>The method takes an optional callback argument which will be called when finished.</p>
<p>This can only be called from the master process.</p>
<h2>cluster.fork([env])<span><a class="mark" href="#cluster_cluster_fork_env" id="cluster_cluster_fork_env">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><ul>
<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Key/value pairs to add to worker process environment.</li>
<li>return <a href="cluster.html#cluster_class_worker" class="type"><cluster.Worker></a></li>
</ul>
<p>Spawn a new worker process.</p>
<p>This can only be called from the master process.</p>
<h2>cluster.isMaster<span><a class="mark" href="#cluster_cluster_ismaster" id="cluster_cluster_ismaster">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.8.1</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>True if the process is a master. This is determined
by the <code>process.env.NODE_UNIQUE_ID</code>. If <code>process.env.NODE_UNIQUE_ID</code> is
undefined, then <code>isMaster</code> is <code>true</code>.</p>
<h2>cluster.isWorker<span><a class="mark" href="#cluster_cluster_isworker" id="cluster_cluster_isworker">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>True if the process is not a master (it is the negation of <code>cluster.isMaster</code>).</p>
<h2>cluster.schedulingPolicy<span><a class="mark" href="#cluster_cluster_schedulingpolicy" id="cluster_cluster_schedulingpolicy">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.2</span>
</div><p>The scheduling policy, either <code>cluster.SCHED_RR</code> for round-robin or
<code>cluster.SCHED_NONE</code> to leave it to the operating system. This is a
global setting and effectively frozen once you spawn the first worker
or call <code>cluster.setupMaster()</code>, whatever comes first.</p>
<p><code>SCHED_RR</code> is the default on all operating systems except Windows.
Windows will change to <code>SCHED_RR</code> once libuv is able to effectively
distribute IOCP handles without incurring a large performance hit.</p>
<p><code>cluster.schedulingPolicy</code> can also be set through the
<code>NODE_CLUSTER_SCHED_POLICY</code> environment variable. Valid
values are <code>"rr"</code> and <code>"none"</code>.</p>
<h2>cluster.settings<span><a class="mark" href="#cluster_cluster_settings" id="cluster_cluster_settings">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.1</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>execArgv</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> list of string arguments passed to the Node.js
executable. (Default=<code>process.execArgv</code>)</li>
<li><code>exec</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> file path to worker file. (Default=<code>process.argv[1]</code>)</li>
<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> string arguments passed to worker.
(Default=<code>process.argv.slice(2)</code>)</li>
<li><code>silent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> whether or not to send output to parent's stdio.
(Default=<code>false</code>)</li>
<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.)</li>
<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.)</li>
</ul>
</li>
</ul>
<p>After calling <code>.setupMaster()</code> (or <code>.fork()</code>) this settings object will contain
the settings, including the default values.</p>
<p>This object is not supposed to be changed or set manually, by you.</p>
<h2>cluster.setupMaster([settings])<span><a class="mark" href="#cluster_cluster_setupmaster_settings" id="cluster_cluster_setupmaster_settings">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.1</span>
</div><ul>
<li><code>settings</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>exec</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> file path to worker file. (Default=<code>process.argv[1]</code>)</li>
<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> string arguments passed to worker.
(Default=<code>process.argv.slice(2)</code>)</li>
<li><code>silent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> whether or not to send output to parent's stdio.
(Default=<code>false</code>)</li>
</ul>
</li>
</ul>
<p><code>setupMaster</code> is used to change the default 'fork' behavior. Once called,
the settings will be present in <code>cluster.settings</code>.</p>
<p>Note that:</p>
<ul>
<li>any settings changes only affect future calls to <code>.fork()</code> and have no
effect on workers that are already running</li>
<li>The <em>only</em> attribute of a worker that cannot be set via <code>.setupMaster()</code> is
the <code>env</code> passed to <code>.fork()</code></li>
<li>the defaults above apply to the first call only, the defaults for later
calls is the current value at the time of <code>cluster.setupMaster()</code> is called</li>
</ul>
<p>Example:</p>
<pre><code class="lang-js">const cluster = require('cluster');
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'https'],
silent: true
});
cluster.fork(); // https worker
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'http']
});
cluster.fork(); // http worker
</code></pre>
<p>This can only be called from the master process.</p>
<h2>cluster.worker<span><a class="mark" href="#cluster_cluster_worker" id="cluster_cluster_worker">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>A reference to the current worker object. Not available in the master process.</p>
<pre><code class="lang-js">const cluster = require('cluster');
if (cluster.isMaster) {
console.log('I am master');
cluster.fork();
cluster.fork();
} else if (cluster.isWorker) {
console.log(`I am worker #${cluster.worker.id}`);
}
</code></pre>
<h2>cluster.workers<span><a class="mark" href="#cluster_cluster_workers" id="cluster_cluster_workers">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>A hash that stores the active worker objects, keyed by <code>id</code> field. Makes it
easy to loop through all the workers. It is only available in the master
process.</p>
<p>A worker is removed from cluster.workers after the worker has disconnected <em>and</em>
exited. The order between these two events cannot be determined in advance.
However, it is guaranteed that the removal from the cluster.workers list happens
before last <code>'disconnect'</code> or <code>'exit'</code> event is emitted.</p>
<pre><code class="lang-js">// Go through all workers
function eachWorker(callback) {
for (var id in cluster.workers) {
callback(cluster.workers[id]);
}
}
eachWorker((worker) => {
worker.send('big announcement to all workers');
});
</code></pre>
<p>Should you wish to reference a worker over a communication channel, using
the worker's unique id is the easiest way to find the worker.</p>
<pre><code class="lang-js">socket.on('data', (id) => {
var worker = cluster.workers[id];
});
</code></pre>
<!-- [end-include:cluster.md] -->
<!-- [start-include:cli.md] -->
<h1>Command Line Options<span><a class="mark" href="#cli_command_line_options" id="cli_command_line_options">#</a></span></h1>
<!--type=misc-->
<p>Node.js comes with a variety of CLI options. These options expose built-in
debugging, multiple ways to execute scripts, and other helpful runtime options.</p>
<p>To view this documentation as a manual page in your terminal, run <code>man node</code>.</p>
<h2>Synopsis<span><a class="mark" href="#cli_synopsis" id="cli_synopsis">#</a></span></h2>
<p><code>node [options] [v8 options] [script.js | -e "script"] [arguments]</code></p>
<p><code>node debug [script.js | -e "script" | <host>:<port>] …</code></p>
<p><code>node --v8-options</code></p>
<p>Execute without arguments to start the <a href="repl.html">REPL</a>.</p>
<p><em>For more info about <code>node debug</code>, please see the <a href="debugger.html">debugger</a> documentation.</em></p>
<h2>Options<span><a class="mark" href="#cli_options" id="cli_options">#</a></span></h2>
<h3><code>-v</code>, <code>--version</code><span><a class="mark" href="#cli_v_version" id="cli_v_version">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.3</span>
</div><p>Print node's version.</p>
<h3><code>-h</code>, <code>--help</code><span><a class="mark" href="#cli_h_help" id="cli_h_help">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.3</span>
</div><p>Print node command line options.
The output of this option is less detailed than this document.</p>
<h3><code>-e</code>, <code>--eval "script"</code><span><a class="mark" href="#cli_e_eval_script" id="cli_e_eval_script">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.2</span>
</div><p>Evaluate the following argument as JavaScript.</p>
<h3><code>-p</code>, <code>--print "script"</code><span><a class="mark" href="#cli_p_print_script" id="cli_p_print_script">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.4</span>
</div><p>Identical to <code>-e</code> but prints the result.</p>
<h3><code>-c</code>, <code>--check</code><span><a class="mark" href="#cli_c_check" id="cli_c_check">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.2.0</span>
</div><p>Syntax check the script without executing.</p>
<h3><code>-i</code>, <code>--interactive</code><span><a class="mark" href="#cli_i_interactive" id="cli_i_interactive">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>Opens the REPL even if stdin does not appear to be a terminal.</p>
<h3><code>-r</code>, <code>--require module</code><span><a class="mark" href="#cli_r_require_module" id="cli_r_require_module">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.6.0</span>
</div><p>Preload the specified module at startup.</p>
<p>Follows <code>require()</code>'s module resolution
rules. <code>module</code> may be either a path to a file, or a node module name.</p>
<h3><code>--no-deprecation</code><span><a class="mark" href="#cli_no_deprecation" id="cli_no_deprecation">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.8.0</span>
</div><p>Silence deprecation warnings.</p>
<h3><code>--trace-deprecation</code><span><a class="mark" href="#cli_trace_deprecation" id="cli_trace_deprecation">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.8.0</span>
</div><p>Print stack traces for deprecations.</p>
<h3><code>--throw-deprecation</code><span><a class="mark" href="#cli_throw_deprecation" id="cli_throw_deprecation">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Throw errors for deprecations.</p>
<h3><code>--trace-sync-io</code><span><a class="mark" href="#cli_trace_sync_io" id="cli_trace_sync_io">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v2.1.0</span>
</div><p>Prints a stack trace whenever synchronous I/O is detected after the first turn
of the event loop.</p>
<h3><code>--zero-fill-buffers</code><span><a class="mark" href="#cli_zero_fill_buffers" id="cli_zero_fill_buffers">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.5.0</span>
</div><p>Automatically zero-fills all newly allocated <a href="buffer.html">Buffer</a> and <a href="buffer.html#buffer_class_slowbuffer">SlowBuffer</a>
instances.</p>
<h3><code>--track-heap-objects</code><span><a class="mark" href="#cli_track_heap_objects" id="cli_track_heap_objects">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v2.4.0</span>
</div><p>Track heap object allocations for heap snapshots.</p>
<h3><code>--prof-process</code><span><a class="mark" href="#cli_prof_process" id="cli_prof_process">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.4.0</span>
</div><p>Process v8 profiler output generated using the v8 option <code>--prof</code>.</p>
<h3><code>--v8-options</code><span><a class="mark" href="#cli_v8_options" id="cli_v8_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.3</span>
</div><p>Print v8 command line options.</p>
<h3><code>--tls-cipher-list=list</code><span><a class="mark" href="#cli_tls_cipher_list_list" id="cli_tls_cipher_list_list">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v4.0.0</span>
</div><p>Specify an alternative default TLS cipher list. (Requires Node.js to be built
with crypto support. (Default))</p>
<h3><code>--enable-fips</code><span><a class="mark" href="#cli_enable_fips" id="cli_enable_fips">#</a></span></h3>
<p>Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with
<code>./configure --openssl-fips</code>)</p>
<h3><code>--force-fips</code><span><a class="mark" href="#cli_force_fips" id="cli_force_fips">#</a></span></h3>
<p>Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.)
(Same requirements as <code>--enable-fips</code>)</p>
<h3><code>--icu-data-dir=file</code><span><a class="mark" href="#cli_icu_data_dir_file" id="cli_icu_data_dir_file">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.15</span>
</div><p>Specify ICU data load path. (overrides <code>NODE_ICU_DATA</code>)</p>
<h2>Environment Variables<span><a class="mark" href="#cli_environment_variables" id="cli_environment_variables">#</a></span></h2>
<h3><code>NODE_DEBUG=module[,…]</code><span><a class="mark" href="#cli_node_debug_module" id="cli_node_debug_module">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.32</span>
</div><p><code>','</code>-separated list of core modules that should print debug information.</p>
<h3><code>NODE_PATH=path[:…]</code><span><a class="mark" href="#cli_node_path_path" id="cli_node_path_path">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.32</span>
</div><p><code>':'</code>-separated list of directories prefixed to the module search path.</p>
<p><em>Note: on Windows, this is a <code>';'</code>-separated list instead.</em></p>
<h3><code>NODE_DISABLE_COLORS=1</code><span><a class="mark" href="#cli_node_disable_colors_1" id="cli_node_disable_colors_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>When set to <code>1</code> colors will not be used in the REPL.</p>
<h3><code>NODE_ICU_DATA=file</code><span><a class="mark" href="#cli_node_icu_data_file" id="cli_node_icu_data_file">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.15</span>
</div><p>Data path for ICU (Intl object) data. Will extend linked-in data when compiled
with small-icu support.</p>
<h3><code>NODE_REPL_HISTORY=file</code><span><a class="mark" href="#cli_node_repl_history_file" id="cli_node_repl_history_file">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v3.0.0</span>
</div><p>Path to the file used to store the persistent REPL history. The default path is
<code>~/.node_repl_history</code>, which is overridden by this variable. Setting the value
to an empty string (<code>""</code> or <code>" "</code>) disables persistent REPL history.</p>
<h3><code>NODE_EXTRA_CA_CERTS=file</code><span><a class="mark" href="#cli_node_extra_ca_certs_file" id="cli_node_extra_ca_certs_file">#</a></span></h3>
<div class="api_metadata">
<span>Added in: XXX</span>
</div><p>When set, the well known "root" CAs (like VeriSign) will be extended with the
extra certificates in <code>file</code>. The file should consist of one or more trusted
certificates in PEM format. A message will be printed to stderr (once)
if the file is missing or
misformatted, but any errors are otherwise ignored.</p>
<p>Note that neither the well known nor extra certificates are used when the <code>ca</code>
options property is explicitly specified for a TLS or HTTPS client or server.</p>
<!-- [end-include:cli.md] -->
<!-- [start-include:console.md] -->
<h1>Console<span><a class="mark" href="#console_console" id="console_console">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>The <code>console</code> module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.</p>
<p>The module exports two specific components:</p>
<ul>
<li>A <code>Console</code> class with methods such as <code>console.log()</code>, <code>console.error()</code> and
<code>console.warn()</code> that can be used to write to any Node.js stream.</li>
<li>A global <code>console</code> instance configured to write to <code>stdout</code> and <code>stderr</code>.
Because this object is global, it can be used without calling
<code>require('console')</code>.</li>
</ul>
<p>Example using the global <code>console</code>:</p>
<pre><code class="lang-js">console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to stderr
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
</code></pre>
<p>Example using the <code>Console</code> class:</p>
<pre><code class="lang-js">const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
</code></pre>
<p>While the API for the <code>Console</code> class is designed fundamentally around the
browser <code>console</code> object, the <code>Console</code> in Node.js is <em>not</em> intended to
duplicate the browser's functionality exactly.</p>
<h2>Asynchronous vs Synchronous Consoles<span><a class="mark" href="#console_asynchronous_vs_synchronous_consoles" id="console_asynchronous_vs_synchronous_consoles">#</a></span></h2>
<p>The console functions are usually asynchronous unless the destination is a file.
Disks are fast and operating systems normally employ write-back caching;
it should be a very rare occurrence indeed that a write blocks, but it
is possible.</p>
<p>Additionally, console functions are blocking when outputting to TTYs
(terminals) on OS X as a workaround for the OS's very small, 1kb buffer size.
This is to prevent interleaving between <code>stdout</code> and <code>stderr</code>.</p>
<h2>Class: Console<span><a class="mark" href="#console_class_console" id="console_class_console">#</a></span></h2>
<!--type=class-->
<p>The <code>Console</code> class can be used to create a simple logger with configurable
output streams and can be accessed using either <code>require('console').Console</code>
or <code>console.Console</code>:</p>
<pre><code class="lang-js">const Console = require('console').Console;
const Console = console.Console;
</code></pre>
<h3>new Console(stdout[, stderr])<span><a class="mark" href="#console_new_console_stdout_stderr" id="console_new_console_stdout_stderr">#</a></span></h3>
<p>Creates a new <code>Console</code> by passing one or two writable stream instances.
<code>stdout</code> is a writable stream to print log or info output. <code>stderr</code>
is used for warning or error output. If <code>stderr</code> isn't passed, warning and error
output will be sent to <code>stdout</code>.</p>
<pre><code class="lang-js">const output = fs.createWriteStream('./stdout.log');
const errorOutput = fs.createWriteStream('./stderr.log');
// custom simple logger
const logger = new Console(output, errorOutput);
// use it like console
const count = 5;
logger.log('count: %d', count);
// in stdout.log: count 5
</code></pre>
<p>The global <code>console</code> is a special <code>Console</code> whose output is sent to
<a href="process.html#process_process_stdout"><code>process.stdout</code></a> and <a href="process.html#process_process_stderr"><code>process.stderr</code></a>. It is equivalent to calling:</p>
<pre><code class="lang-js">new Console(process.stdout, process.stderr);
</code></pre>
<h3>console.assert(value[, message][, ...])<span><a class="mark" href="#console_console_assert_value_message" id="console_console_assert_value_message">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.101</span>
</div><p>A simple assertion test that verifies whether <code>value</code> is truthy. If it is not,
an <code>AssertionError</code> is thrown. If provided, the error <code>message</code> is formatted
using <a href="util.html#util_util_format_format"><code>util.format()</code></a> and used as the error message.</p>
<pre><code class="lang-js">console.assert(true, 'does nothing');
// OK
console.assert(false, 'Whoops %s', 'didn\'t work');
// AssertionError: Whoops didn't work
</code></pre>
<p><em>Note: the <code>console.assert()</code> method is implemented differently in Node.js
than the <code>console.assert()</code> method <a href="https://developer.mozilla.org/en-US/docs/Web/API/console/assert">available in browsers</a>.</em></p>
<p>Specifically, in browsers, calling <code>console.assert()</code> with a falsy
assertion will cause the <code>message</code> to be printed to the console without
interrupting execution of subsequent code. In Node.js, however, a falsy
assertion will cause an <code>AssertionError</code> to be thrown.</p>
<p>Functionality approximating that implemented by browsers can be implemented
by extending Node.js' <code>console</code> and overriding the <code>console.assert()</code> method.</p>
<p>In the following example, a simple module is created that extends and overrides
the default behavior of <code>console</code> in Node.js.</p>
<pre><code class="lang-js">'use strict';
// Creates a simple extension of console with a
// new impl for assert without monkey-patching.
const myConsole = Object.create(console, {
assert: {
value: function assert(assertion, message, ...args) {
try {
console.assert(assertion, message, ...args);
} catch (err) {
console.error(err.stack);
}
},
configurable: true,
enumerable: true,
writable: true,
},
});
module.exports = myConsole;
</code></pre>
<p>This can then be used as a direct replacement for the built in console:</p>
<pre><code class="lang-js">const console = require('./myConsole');
console.assert(false, 'this message will print, but no error thrown');
console.log('this will also print');
</code></pre>
<h3>console.dir(obj[, options])<span><a class="mark" href="#console_console_dir_obj_options" id="console_console_dir_obj_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.101</span>
</div><p>Uses <a href="util.html#util_util_inspect_object_options"><code>util.inspect()</code></a> on <code>obj</code> and prints the resulting string to <code>stdout</code>.
This function bypasses any custom <code>inspect()</code> function defined on <code>obj</code>. An
optional <code>options</code> object may be passed to alter certain aspects of the
formatted string:</p>
<ul>
<li><p><code>showHidden</code> - if <code>true</code> then the object's non-enumerable and symbol
properties will be shown too. Defaults to <code>false</code>.</p>
</li>
<li><p><code>depth</code> - tells <a href="util.html#util_util_inspect_object_options"><code>util.inspect()</code></a> how many times to recurse while
formatting the object. This is useful for inspecting large complicated objects.
Defaults to <code>2</code>. To make it recurse indefinitely, pass <code>null</code>.</p>
</li>
<li><p><code>colors</code> - if <code>true</code>, then the output will be styled with ANSI color codes.
Defaults to <code>false</code>. Colors are customizable; see
<a href="util.html#util_customizing_util_inspect_colors">customizing <code>util.inspect()</code> colors</a>.</p>
</li>
</ul>
<h3>console.error([data][, ...])<span><a class="mark" href="#console_console_error_data" id="console_console_error_data">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.100</span>
</div><p>Prints to <code>stderr</code> with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to <a href="http://man7.org/linux/man-pages/man3/printf.3.html">printf(3)</a> (the arguments are all passed to
<a href="util.html#util_util_format_format"><code>util.format()</code></a>).</p>
<pre><code class="lang-js">const code = 5;
console.error('error #%d', code);
// Prints: error #5, to stderr
console.error('error', code);
// Prints: error 5, to stderr
</code></pre>
<p>If formatting elements (e.g. <code>%d</code>) are not found in the first string then
<a href="util.html#util_util_inspect_object_options"><code>util.inspect()</code></a> is called on each argument and the resulting string
values are concatenated. See <a href="util.html#util_util_format_format"><code>util.format()</code></a> for more information.</p>
<h3>console.info([data][, ...])<span><a class="mark" href="#console_console_info_data" id="console_console_info_data">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.100</span>
</div><p>The <code>console.info()</code> function is an alias for <a href="console.html#console_console_log_data"><code>console.log()</code></a>.</p>
<h3>console.log([data][, ...])<span><a class="mark" href="#console_console_log_data" id="console_console_log_data">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.100</span>
</div><p>Prints to <code>stdout</code> with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to <a href="http://man7.org/linux/man-pages/man3/printf.3.html">printf(3)</a> (the arguments are all passed to
<a href="util.html#util_util_format_format"><code>util.format()</code></a>).</p>
<pre><code class="lang-js">const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
</code></pre>
<p>If formatting elements (e.g. <code>%d</code>) are not found in the first string then
<a href="util.html#util_util_inspect_object_options"><code>util.inspect()</code></a> is called on each argument and the resulting string
values are concatenated. See <a href="util.html#util_util_format_format"><code>util.format()</code></a> for more information.</p>
<h3>console.time(label)<span><a class="mark" href="#console_console_time_label" id="console_console_time_label">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.104</span>
</div><p>Used to calculate the duration of a specific operation. To start a timer, call
the <code>console.time()</code> method, giving it a unique <code>label</code> as the only parameter. To stop the
timer, and to get the elapsed time in milliseconds, just call the
<a href="#console_console_timeend_label"><code>console.timeEnd()</code></a> method, again passing the
timer's unique <code>label</code> as the parameter.</p>
<h3>console.timeEnd(label)<span><a class="mark" href="#console_console_timeend_label" id="console_console_timeend_label">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.104</span>
</div><p>Stops a timer that was previously started by calling <a href="#console_console_time_label"><code>console.time()</code></a> and
prints the result to stdout:</p>
<pre><code class="lang-js">console.time('100-elements');
for (let i = 0; i < 100; i++) {
;
}
console.timeEnd('100-elements');
// prints 100-elements: 262ms
</code></pre>
<h3>console.trace(message[, ...])<span><a class="mark" href="#console_console_trace_message" id="console_console_trace_message">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.104</span>
</div><p>Prints to <code>stderr</code> the string <code>'Trace :'</code>, followed by the <a href="util.html#util_util_format_format"><code>util.format()</code></a>
formatted message and stack trace to the current position in the code.</p>
<pre><code class="lang-js">console.trace('Show me');
// Prints: (stack trace will vary based on where trace is called)
// Trace: Show me
// at repl:2:9
// at REPLServer.defaultEval (repl.js:248:27)
// at bound (domain.js:287:14)
// at REPLServer.runBound [as eval] (domain.js:300:12)
// at REPLServer.<anonymous> (repl.js:412:12)
// at emitOne (events.js:82:20)
// at REPLServer.emit (events.js:169:7)
// at REPLServer.Interface._onLine (readline.js:210:10)
// at REPLServer.Interface._line (readline.js:549:8)
// at REPLServer.Interface._ttyWrite (readline.js:826:14)
</code></pre>
<h3>console.warn([data][, ...])<span><a class="mark" href="#console_console_warn_data" id="console_console_warn_data">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.100</span>
</div><p>The <code>console.warn()</code> function is an alias for <a href="console.html#console_console_error_data"><code>console.error()</code></a>.</p>
<!-- [end-include:console.md] -->
<!-- [start-include:crypto.md] -->
<h1>Crypto<span><a class="mark" href="#crypto_crypto" id="crypto_crypto">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>The <code>crypto</code> module provides cryptographic functionality that includes a set of
wrappers for OpenSSL's hash, HMAC, cipher, decipher, sign and verify functions.</p>
<p>Use <code>require('crypto')</code> to access this module.</p>
<pre><code class="lang-js">const crypto = require('crypto');
const secret = 'abcdefg';
const hash = crypto.createHmac('sha256', secret)
.update('I love cupcakes')
.digest('hex');
console.log(hash);
// Prints:
// c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
</code></pre>
<h2>Class: Certificate<span><a class="mark" href="#crypto_class_certificate" id="crypto_class_certificate">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.8</span>
</div><p>SPKAC is a Certificate Signing Request mechanism originally implemented by
Netscape and now specified formally as part of <a href="http://www.w3.org/TR/html5/forms.html#the-keygen-element">HTML5's <code>keygen</code> element</a>.</p>
<p>The <code>crypto</code> module provides the <code>Certificate</code> class for working with SPKAC
data. The most common usage is handling output generated by the HTML5
<code><keygen></code> element. Node.js uses <a href="https://www.openssl.org/docs/apps/spkac.html">OpenSSL's SPKAC implementation</a> internally.</p>
<h3>new crypto.Certificate()<span><a class="mark" href="#crypto_new_crypto_certificate" id="crypto_new_crypto_certificate">#</a></span></h3>
<p>Instances of the <code>Certificate</code> class can be created using the <code>new</code> keyword
or by calling <code>crypto.Certificate()</code> as a function:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const cert1 = new crypto.Certificate();
const cert2 = crypto.Certificate();
</code></pre>
<h3>certificate.exportChallenge(spkac)<span><a class="mark" href="#crypto_certificate_exportchallenge_spkac" id="crypto_certificate_exportchallenge_spkac">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.8</span>
</div><p>The <code>spkac</code> data structure includes a public key and a challenge. The
<code>certificate.exportChallenge()</code> returns the challenge component in the
form of a Node.js <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>. The <code>spkac</code> argument can be either a string
or a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<pre><code class="lang-js">const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const challenge = cert.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints the challenge as a UTF8 string
</code></pre>
<h3>certificate.exportPublicKey(spkac)<span><a class="mark" href="#crypto_certificate_exportpublickey_spkac" id="crypto_certificate_exportpublickey_spkac">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.8</span>
</div><p>The <code>spkac</code> data structure includes a public key and a challenge. The
<code>certificate.exportPublicKey()</code> returns the public key component in the
form of a Node.js <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>. The <code>spkac</code> argument can be either a string
or a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<pre><code class="lang-js">const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const publicKey = cert.exportPublicKey(spkac);
console.log(publicKey);
// Prints the public key as <Buffer ...>
</code></pre>
<h3>certificate.verifySpkac(spkac)<span><a class="mark" href="#crypto_certificate_verifyspkac_spkac" id="crypto_certificate_verifyspkac_spkac">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.8</span>
</div><p>Returns <code>true</code> if the given <code>spkac</code> data structure is valid, <code>false</code> otherwise.
The <code>spkac</code> argument must be a Node.js <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<pre><code class="lang-js">const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
console.log(cert.verifySpkac(new Buffer(spkac)));
// Prints true or false
</code></pre>
<h2>Class: Cipher<span><a class="mark" href="#crypto_class_cipher" id="crypto_class_cipher">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Instances of the <code>Cipher</code> class are used to encrypt data. The class can be
used in one of two ways:</p>
<ul>
<li>As a <a href="stream.html#stream_stream">stream</a> that is both readable and writable, where plain unencrypted
data is written to produce encrypted data on the readable side, or</li>
<li>Using the <a href="#crypto_cipher_update_data_input_encoding_output_encoding"><code>cipher.update()</code></a> and <a href="#crypto_cipher_final_output_encoding"><code>cipher.final()</code></a> methods to produce
the encrypted data.</li>
</ul>
<p>The <a href="#crypto_crypto_createcipher_algorithm_password"><code>crypto.createCipher()</code></a> or <a href="#crypto_crypto_createcipheriv_algorithm_key_iv"><code>crypto.createCipheriv()</code></a> methods are
used to create <code>Cipher</code> instances. <code>Cipher</code> objects are not to be created
directly using the <code>new</code> keyword.</p>
<p>Example: Using <code>Cipher</code> objects as streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const cipher = crypto.createCipher('aes192', 'a password');
var encrypted = '';
cipher.on('readable', () => {
var data = cipher.read();
if (data)
encrypted += data.toString('hex');
});
cipher.on('end', () => {
console.log(encrypted);
// Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
});
cipher.write('some clear text data');
cipher.end();
</code></pre>
<p>Example: Using <code>Cipher</code> and piped streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const fs = require('fs');
const cipher = crypto.createCipher('aes192', 'a password');
const input = fs.createReadStream('test.js');
const output = fs.createWriteStream('test.enc');
input.pipe(cipher).pipe(output);
</code></pre>
<p>Example: Using the <a href="#crypto_cipher_update_data_input_encoding_output_encoding"><code>cipher.update()</code></a> and <a href="#crypto_cipher_final_output_encoding"><code>cipher.final()</code></a> methods:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const cipher = crypto.createCipher('aes192', 'a password');
var encrypted = cipher.update('some clear text data', 'utf8', 'hex');
encrypted += cipher.final('hex');
console.log(encrypted);
// Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
</code></pre>
<h3>cipher.final([output_encoding])<span><a class="mark" href="#crypto_cipher_final_output_encoding" id="crypto_cipher_final_output_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Returns any remaining enciphered contents. If <code>output_encoding</code>
parameter is one of <code>'binary'</code>, <code>'base64'</code> or <code>'hex'</code>, a string is returned.
If an <code>output_encoding</code> is not provided, a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<p>Once the <code>cipher.final()</code> method has been called, the <code>Cipher</code> object can no
longer be used to encrypt data. Attempts to call <code>cipher.final()</code> more than
once will result in an error being thrown.</p>
<h3>cipher.setAAD(buffer)<span><a class="mark" href="#crypto_cipher_setaad_buffer" id="crypto_cipher_setaad_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><p>When using an authenticated encryption mode (only <code>GCM</code> is currently
supported), the <code>cipher.setAAD()</code> method sets the value used for the
<em>additional authenticated data</em> (AAD) input parameter.</p>
<h3>cipher.getAuthTag()<span><a class="mark" href="#crypto_cipher_getauthtag" id="crypto_cipher_getauthtag">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><p>When using an authenticated encryption mode (only <code>GCM</code> is currently
supported), the <code>cipher.getAuthTag()</code> method returns a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> containing
the <em>authentication tag</em> that has been computed from the given data.</p>
<p>The <code>cipher.getAuthTag()</code> method should only be called after encryption has
been completed using the <a href="#crypto_cipher_final_output_encoding"><code>cipher.final()</code></a> method.</p>
<h3>cipher.setAutoPadding(auto_padding=true)<span><a class="mark" href="#crypto_cipher_setautopadding_auto_padding_true" id="crypto_cipher_setautopadding_auto_padding_true">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.1</span>
</div><p>When using block encryption algorithms, the <code>Cipher</code> class will automatically
add padding to the input data to the appropriate block size. To disable the
default padding call <code>cipher.setAutoPadding(false)</code>.</p>
<p>When <code>auto_padding</code> is <code>false</code>, the length of the entire input data must be a
multiple of the cipher's block size or <a href="#crypto_cipher_final_output_encoding"><code>cipher.final()</code></a> will throw an Error.
Disabling automatic padding is useful for non-standard padding, for instance
using <code>0x0</code> instead of PKCS padding.</p>
<p>The <code>cipher.setAutoPadding()</code> method must be called before <a href="#crypto_cipher_final_output_encoding"><code>cipher.final()</code></a>.</p>
<h3>cipher.update(data[, input_encoding][, output_encoding])<span><a class="mark" href="#crypto_cipher_update_data_input_encoding_output_encoding" id="crypto_cipher_update_data_input_encoding_output_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Updates the cipher with <code>data</code>. If the <code>input_encoding</code> argument is given,
it's value must be one of <code>'utf8'</code>, <code>'ascii'</code>, or <code>'binary'</code> and the <code>data</code>
argument is a string using the specified encoding. If the <code>input_encoding</code>
argument is not given, <code>data</code> must be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>. If <code>data</code> is a
<a href="buffer.html#buffer_buffer"><code>Buffer</code></a> then <code>input_encoding</code> is ignored.</p>
<p>The <code>output_encoding</code> specifies the output format of the enciphered
data, and can be <code>'binary'</code>, <code>'base64'</code> or <code>'hex'</code>. If the <code>output_encoding</code>
is specified, a string using the specified encoding is returned. If no
<code>output_encoding</code> is provided, a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<p>The <code>cipher.update()</code> method can be called multiple times with new data until
<a href="#crypto_cipher_final_output_encoding"><code>cipher.final()</code></a> is called. Calling <code>cipher.update()</code> after
<a href="#crypto_cipher_final_output_encoding"><code>cipher.final()</code></a> will result in an error being thrown.</p>
<h2>Class: Decipher<span><a class="mark" href="#crypto_class_decipher" id="crypto_class_decipher">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Instances of the <code>Decipher</code> class are used to decrypt data. The class can be
used in one of two ways:</p>
<ul>
<li>As a <a href="stream.html#stream_stream">stream</a> that is both readable and writable, where plain encrypted
data is written to produce unencrypted data on the readable side, or</li>
<li>Using the <a href="#crypto_decipher_update_data_input_encoding_output_encoding"><code>decipher.update()</code></a> and <a href="#crypto_decipher_final_output_encoding"><code>decipher.final()</code></a> methods to
produce the unencrypted data.</li>
</ul>
<p>The <a href="#crypto_crypto_createdecipher_algorithm_password"><code>crypto.createDecipher()</code></a> or <a href="#crypto_crypto_createdecipheriv_algorithm_key_iv"><code>crypto.createDecipheriv()</code></a> methods are
used to create <code>Decipher</code> instances. <code>Decipher</code> objects are not to be created
directly using the <code>new</code> keyword.</p>
<p>Example: Using <code>Decipher</code> objects as streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const decipher = crypto.createDecipher('aes192', 'a password');
var decrypted = '';
decipher.on('readable', () => {
var data = decipher.read();
if (data)
decrypted += data.toString('utf8');
});
decipher.on('end', () => {
console.log(decrypted);
// Prints: some clear text data
});
var encrypted = 'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
decipher.write(encrypted, 'hex');
decipher.end();
</code></pre>
<p>Example: Using <code>Decipher</code> and piped streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const fs = require('fs');
const decipher = crypto.createDecipher('aes192', 'a password');
const input = fs.createReadStream('test.enc');
const output = fs.createWriteStream('test.js');
input.pipe(decipher).pipe(output);
</code></pre>
<p>Example: Using the <a href="#crypto_decipher_update_data_input_encoding_output_encoding"><code>decipher.update()</code></a> and <a href="#crypto_decipher_final_output_encoding"><code>decipher.final()</code></a> methods:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const decipher = crypto.createDecipher('aes192', 'a password');
var encrypted = 'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
var decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');
console.log(decrypted);
// Prints: some clear text data
</code></pre>
<h3>decipher.final([output_encoding])<span><a class="mark" href="#crypto_decipher_final_output_encoding" id="crypto_decipher_final_output_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Returns any remaining deciphered contents. If <code>output_encoding</code>
parameter is one of <code>'binary'</code>, <code>'base64'</code> or <code>'hex'</code>, a string is returned.
If an <code>output_encoding</code> is not provided, a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<p>Once the <code>decipher.final()</code> method has been called, the <code>Decipher</code> object can
no longer be used to decrypt data. Attempts to call <code>decipher.final()</code> more
than once will result in an error being thrown.</p>
<h3>decipher.setAAD(buffer)<span><a class="mark" href="#crypto_decipher_setaad_buffer" id="crypto_decipher_setaad_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><p>When using an authenticated encryption mode (only <code>GCM</code> is currently
supported), the <code>decipher.setAAD()</code> method sets the value used for the
<em>additional authenticated data</em> (AAD) input parameter.</p>
<h3>decipher.setAuthTag(buffer)<span><a class="mark" href="#crypto_decipher_setauthtag_buffer" id="crypto_decipher_setauthtag_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><p>When using an authenticated encryption mode (only <code>GCM</code> is currently
supported), the <code>decipher.setAuthTag()</code> method is used to pass in the
received <em>authentication tag</em>. If no tag is provided, or if the cipher text
has been tampered with, <a href="#crypto_decipher_final_output_encoding"><code>decipher.final()</code></a> with throw, indicating that the
cipher text should be discarded due to failed authentication.</p>
<h3>decipher.setAutoPadding(auto_padding=true)<span><a class="mark" href="#crypto_decipher_setautopadding_auto_padding_true" id="crypto_decipher_setautopadding_auto_padding_true">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.1</span>
</div><p>When data has been encrypted without standard block padding, calling
<code>decipher.setAutoPadding(false)</code> will disable automatic padding to prevent
<a href="#crypto_decipher_final_output_encoding"><code>decipher.final()</code></a> from checking for and removing padding.</p>
<p>Turning auto padding off will only work if the input data's length is a
multiple of the ciphers block size.</p>
<p>The <code>decipher.setAutoPadding()</code> method must be called before
<a href="#crypto_decipher_update_data_input_encoding_output_encoding"><code>decipher.update()</code></a>.</p>
<h3>decipher.update(data[, input_encoding][, output_encoding])<span><a class="mark" href="#crypto_decipher_update_data_input_encoding_output_encoding" id="crypto_decipher_update_data_input_encoding_output_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Updates the decipher with <code>data</code>. If the <code>input_encoding</code> argument is given,
it's value must be one of <code>'binary'</code>, <code>'base64'</code>, or <code>'hex'</code> and the <code>data</code>
argument is a string using the specified encoding. If the <code>input_encoding</code>
argument is not given, <code>data</code> must be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>. If <code>data</code> is a
<a href="buffer.html#buffer_buffer"><code>Buffer</code></a> then <code>input_encoding</code> is ignored.</p>
<p>The <code>output_encoding</code> specifies the output format of the enciphered
data, and can be <code>'binary'</code>, <code>'ascii'</code> or <code>'utf8'</code>. If the <code>output_encoding</code>
is specified, a string using the specified encoding is returned. If no
<code>output_encoding</code> is provided, a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<p>The <code>decipher.update()</code> method can be called multiple times with new data until
<a href="#crypto_decipher_final_output_encoding"><code>decipher.final()</code></a> is called. Calling <code>decipher.update()</code> after
<a href="#crypto_decipher_final_output_encoding"><code>decipher.final()</code></a> will result in an error being thrown.</p>
<h2>Class: DiffieHellman<span><a class="mark" href="#crypto_class_diffiehellman" id="crypto_class_diffiehellman">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>The <code>DiffieHellman</code> class is a utility for creating Diffie-Hellman key
exchanges.</p>
<p>Instances of the <code>DiffieHellman</code> class can be created using the
<a href="#crypto_crypto_creatediffiehellman_prime_prime_encoding_generator_generator_encoding"><code>crypto.createDiffieHellman()</code></a> function.</p>
<pre><code class="lang-js">const crypto = require('crypto');
const assert = require('assert');
// Generate Alice's keys...
const alice = crypto.createDiffieHellman(2048);
const alice_key = alice.generateKeys();
// Generate Bob's keys...
const bob = crypto.createDiffieHellman(alice.getPrime(), alice.getGenerator());
const bob_key = bob.generateKeys();
// Exchange and generate the secret...
const alice_secret = alice.computeSecret(bob_key);
const bob_secret = bob.computeSecret(alice_key);
// OK
assert.equal(alice_secret.toString('hex'), bob_secret.toString('hex'));
</code></pre>
<h3>diffieHellman.computeSecret(other_public_key[, input_encoding][, output_encoding])<span><a class="mark" href="#crypto_diffiehellman_computesecret_other_public_key_input_encoding_output_encoding" id="crypto_diffiehellman_computesecret_other_public_key_input_encoding_output_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Computes the shared secret using <code>other_public_key</code> as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using the specified <code>input_encoding</code>, and secret is
encoded using specified <code>output_encoding</code>. Encodings can be
<code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If the <code>input_encoding</code> is not
provided, <code>other_public_key</code> is expected to be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<p>If <code>output_encoding</code> is given a string is returned; otherwise, a
<a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<h3>diffieHellman.generateKeys([encoding])<span><a class="mark" href="#crypto_diffiehellman_generatekeys_encoding" id="crypto_diffiehellman_generatekeys_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Generates private and public Diffie-Hellman key values, and returns
the public key in the specified <code>encoding</code>. This key should be
transferred to the other party. Encoding can be <code>'binary'</code>, <code>'hex'</code>,
or <code>'base64'</code>. If <code>encoding</code> is provided a string is returned; otherwise a
<a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<h3>diffieHellman.getGenerator([encoding])<span><a class="mark" href="#crypto_diffiehellman_getgenerator_encoding" id="crypto_diffiehellman_getgenerator_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Returns the Diffie-Hellman generator in the specified <code>encoding</code>, which can
be <code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If <code>encoding</code> is provided a string is
returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<h3>diffieHellman.getPrime([encoding])<span><a class="mark" href="#crypto_diffiehellman_getprime_encoding" id="crypto_diffiehellman_getprime_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Returns the Diffie-Hellman prime in the specified <code>encoding</code>, which can
be <code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If <code>encoding</code> is provided a string is
returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<h3>diffieHellman.getPrivateKey([encoding])<span><a class="mark" href="#crypto_diffiehellman_getprivatekey_encoding" id="crypto_diffiehellman_getprivatekey_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Returns the Diffie-Hellman private key in the specified <code>encoding</code>,
which can be <code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If <code>encoding</code> is provided a
string is returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<h3>diffieHellman.getPublicKey([encoding])<span><a class="mark" href="#crypto_diffiehellman_getpublickey_encoding" id="crypto_diffiehellman_getpublickey_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Returns the Diffie-Hellman public key in the specified <code>encoding</code>, which
can be <code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If <code>encoding</code> is provided a
string is returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<h3>diffieHellman.setPrivateKey(private_key[, encoding])<span><a class="mark" href="#crypto_diffiehellman_setprivatekey_private_key_encoding" id="crypto_diffiehellman_setprivatekey_private_key_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Sets the Diffie-Hellman private key. If the <code>encoding</code> argument is provided
and is either <code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>, <code>private_key</code> is expected
to be a string. If no <code>encoding</code> is provided, <code>private_key</code> is expected
to be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<h3>diffieHellman.setPublicKey(public_key[, encoding])<span><a class="mark" href="#crypto_diffiehellman_setpublickey_public_key_encoding" id="crypto_diffiehellman_setpublickey_public_key_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Sets the Diffie-Hellman public key. If the <code>encoding</code> argument is provided
and is either <code>'binary'</code>, <code>'hex'</code> or <code>'base64'</code>, <code>public_key</code> is expected
to be a string. If no <code>encoding</code> is provided, <code>public_key</code> is expected
to be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<h3>diffieHellman.verifyError<span><a class="mark" href="#crypto_diffiehellman_verifyerror" id="crypto_diffiehellman_verifyerror">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>A bit field containing any warnings and/or errors resulting from a check
performed during initialization of the <code>DiffieHellman</code> object.</p>
<p>The following values are valid for this property (as defined in <code>constants</code>
module):</p>
<ul>
<li><code>DH_CHECK_P_NOT_SAFE_PRIME</code></li>
<li><code>DH_CHECK_P_NOT_PRIME</code></li>
<li><code>DH_UNABLE_TO_CHECK_GENERATOR</code></li>
<li><code>DH_NOT_SUITABLE_GENERATOR</code></li>
</ul>
<h2>Class: ECDH<span><a class="mark" href="#crypto_class_ecdh" id="crypto_class_ecdh">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>The <code>ECDH</code> class is a utility for creating Elliptic Curve Diffie-Hellman (ECDH)
key exchanges.</p>
<p>Instances of the <code>ECDH</code> class can be created using the
<a href="#crypto_crypto_createecdh_curve_name"><code>crypto.createECDH()</code></a> function.</p>
<pre><code class="lang-js">const crypto = require('crypto');
const assert = require('assert');
// Generate Alice's keys...
const alice = crypto.createECDH('secp521r1');
const alice_key = alice.generateKeys();
// Generate Bob's keys...
const bob = crypto.createECDH('secp521r1');
const bob_key = bob.generateKeys();
// Exchange and generate the secret...
const alice_secret = alice.computeSecret(bob_key);
const bob_secret = bob.computeSecret(alice_key);
assert(alice_secret, bob_secret);
// OK
</code></pre>
<h3>ecdh.computeSecret(other_public_key[, input_encoding][, output_encoding])<span><a class="mark" href="#crypto_ecdh_computesecret_other_public_key_input_encoding_output_encoding" id="crypto_ecdh_computesecret_other_public_key_input_encoding_output_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Computes the shared secret using <code>other_public_key</code> as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using specified <code>input_encoding</code>, and the returned secret
is encoded using the specified <code>output_encoding</code>. Encodings can be
<code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If the <code>input_encoding</code> is not
provided, <code>other_public_key</code> is expected to be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<p>If <code>output_encoding</code> is given a string will be returned; otherwise a
<a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<h3>ecdh.generateKeys([encoding[, format]])<span><a class="mark" href="#crypto_ecdh_generatekeys_encoding_format" id="crypto_ecdh_generatekeys_encoding_format">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Generates private and public EC Diffie-Hellman key values, and returns
the public key in the specified <code>format</code> and <code>encoding</code>. This key should be
transferred to the other party.</p>
<p>The <code>format</code> arguments specifies point encoding and can be <code>'compressed'</code>,
<code>'uncompressed'</code>, or <code>'hybrid'</code>. If <code>format</code> is not specified, the point will
be returned in <code>'uncompressed'</code> format.</p>
<p>The <code>encoding</code> argument can be <code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If
<code>encoding</code> is provided a string is returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>
is returned.</p>
<h3>ecdh.getPrivateKey([encoding])<span><a class="mark" href="#crypto_ecdh_getprivatekey_encoding" id="crypto_ecdh_getprivatekey_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Returns the EC Diffie-Hellman private key in the specified <code>encoding</code>,
which can be <code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If <code>encoding</code> is provided
a string is returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<h3>ecdh.getPublicKey([encoding[, format]])<span><a class="mark" href="#crypto_ecdh_getpublickey_encoding_format" id="crypto_ecdh_getpublickey_encoding_format">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Returns the EC Diffie-Hellman public key in the specified <code>encoding</code> and
<code>format</code>.</p>
<p>The <code>format</code> argument specifies point encoding and can be <code>'compressed'</code>,
<code>'uncompressed'</code>, or <code>'hybrid'</code>. If <code>format</code> is not specified the point will be
returned in <code>'uncompressed'</code> format.</p>
<p>The <code>encoding</code> argument can be <code>'binary'</code>, <code>'hex'</code>, or <code>'base64'</code>. If
<code>encoding</code> is specified, a string is returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is
returned.</p>
<h3>ecdh.setPrivateKey(private_key[, encoding])<span><a class="mark" href="#crypto_ecdh_setprivatekey_private_key_encoding" id="crypto_ecdh_setprivatekey_private_key_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Sets the EC Diffie-Hellman private key. The <code>encoding</code> can be <code>'binary'</code>,
<code>'hex'</code> or <code>'base64'</code>. If <code>encoding</code> is provided, <code>private_key</code> is expected
to be a string; otherwise <code>private_key</code> is expected to be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>. If
<code>private_key</code> is not valid for the curve specified when the <code>ECDH</code> object was
created, an error is thrown. Upon setting the private key, the associated
public point (key) is also generated and set in the ECDH object.</p>
<h3>ecdh.setPublicKey(public_key[, encoding])<span><a class="mark" href="#crypto_ecdh_setpublickey_public_key_encoding" id="crypto_ecdh_setpublickey_public_key_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
<span>Deprecated since: v5.2.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Sets the EC Diffie-Hellman public key. Key encoding can be <code>'binary'</code>,
<code>'hex'</code> or <code>'base64'</code>. If <code>encoding</code> is provided <code>public_key</code> is expected to
be a string; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is expected.</p>
<p>Note that there is not normally a reason to call this method because <code>ECDH</code>
only requires a private key and the other party's public key to compute the
shared secret. Typically either <a href="#crypto_ecdh_generatekeys_encoding_format"><code>ecdh.generateKeys()</code></a> or
<a href="#crypto_ecdh_setprivatekey_private_key_encoding"><code>ecdh.setPrivateKey()</code></a> will be called. The <a href="#crypto_ecdh_setprivatekey_private_key_encoding"><code>ecdh.setPrivateKey()</code></a> method
attempts to generate the public point/key associated with the private key being
set.</p>
<p>Example (obtaining a shared secret):</p>
<pre><code class="lang-js">const crypto = require('crypto');
const alice = crypto.createECDH('secp256k1');
const bob = crypto.createECDH('secp256k1');
// Note: This is a shortcut way to specify one of Alice's previous private
// keys. It would be unwise to use such a predictable private key in a real
// application.
alice.setPrivateKey(
crypto.createHash('sha256').update('alice', 'utf8').digest()
);
// Bob uses a newly generated cryptographically strong
// pseudorandom key pair bob.generateKeys();
const alice_secret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bob_secret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
// alice_secret and bob_secret should be the same shared secret value
console.log(alice_secret === bob_secret);
</code></pre>
<h2>Class: Hash<span><a class="mark" href="#crypto_class_hash" id="crypto_class_hash">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>The <code>Hash</code> class is a utility for creating hash digests of data. It can be
used in one of two ways:</p>
<ul>
<li>As a <a href="stream.html#stream_stream">stream</a> that is both readable and writable, where data is written
to produce a computed hash digest on the readable side, or</li>
<li>Using the <a href="#crypto_hash_update_data_input_encoding"><code>hash.update()</code></a> and <a href="#crypto_hash_digest_encoding"><code>hash.digest()</code></a> methods to produce the
computed hash.</li>
</ul>
<p>The <a href="#crypto_crypto_createhash_algorithm"><code>crypto.createHash()</code></a> method is used to create <code>Hash</code> instances. <code>Hash</code>
objects are not to be created directly using the <code>new</code> keyword.</p>
<p>Example: Using <code>Hash</code> objects as streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const hash = crypto.createHash('sha256');
hash.on('readable', () => {
var data = hash.read();
if (data)
console.log(data.toString('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
});
hash.write('some data to hash');
hash.end();
</code></pre>
<p>Example: Using <code>Hash</code> and piped streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');
const input = fs.createReadStream('test.js');
input.pipe(hash).pipe(process.stdout);
</code></pre>
<p>Example: Using the <a href="#crypto_hash_update_data_input_encoding"><code>hash.update()</code></a> and <a href="#crypto_hash_digest_encoding"><code>hash.digest()</code></a> methods:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const hash = crypto.createHash('sha256');
hash.update('some data to hash');
console.log(hash.digest('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
</code></pre>
<h3>hash.digest([encoding])<span><a class="mark" href="#crypto_hash_digest_encoding" id="crypto_hash_digest_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Calculates the digest of all of the data passed to be hashed (using the
<a href="#crypto_hash_update_data_input_encoding"><code>hash.update()</code></a> method). The <code>encoding</code> can be <code>'hex'</code>, <code>'binary'</code> or
<code>'base64'</code>. If <code>encoding</code> is provided a string will be returned; otherwise
a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned.</p>
<p>The <code>Hash</code> object can not be used again after <code>hash.digest()</code> method has been
called. Multiple calls will cause an error to be thrown.</p>
<h3>hash.update(data[, input_encoding])<span><a class="mark" href="#crypto_hash_update_data_input_encoding" id="crypto_hash_update_data_input_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Updates the hash content with the given <code>data</code>, the encoding of which
is given in <code>input_encoding</code> and can be <code>'utf8'</code>, <code>'ascii'</code> or
<code>'binary'</code>. If <code>encoding</code> is not provided, and the <code>data</code> is a string, an
encoding of <code>'binary'</code> is enforced. If <code>data</code> is a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> then
<code>input_encoding</code> is ignored.</p>
<p>This can be called many times with new data as it is streamed.</p>
<h2>Class: Hmac<span><a class="mark" href="#crypto_class_hmac" id="crypto_class_hmac">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>The <code>Hmac</code> Class is a utility for creating cryptographic HMAC digests. It can
be used in one of two ways:</p>
<ul>
<li>As a <a href="stream.html#stream_stream">stream</a> that is both readable and writable, where data is written
to produce a computed HMAC digest on the readable side, or</li>
<li>Using the <a href="#crypto_hmac_update_data"><code>hmac.update()</code></a> and <a href="#crypto_hmac_digest_encoding"><code>hmac.digest()</code></a> methods to produce the
computed HMAC digest.</li>
</ul>
<p>The <a href="#crypto_crypto_createhmac_algorithm_key"><code>crypto.createHmac()</code></a> method is used to create <code>Hmac</code> instances. <code>Hmac</code>
objects are not to be created directly using the <code>new</code> keyword.</p>
<p>Example: Using <code>Hmac</code> objects as streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');
hmac.on('readable', () => {
var data = hmac.read();
if (data)
console.log(data.toString('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
});
hmac.write('some data to hash');
hmac.end();
</code></pre>
<p>Example: Using <code>Hmac</code> and piped streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');
const input = fs.createReadStream('test.js');
input.pipe(hmac).pipe(process.stdout);
</code></pre>
<p>Example: Using the <a href="#crypto_hmac_update_data"><code>hmac.update()</code></a> and <a href="#crypto_hmac_digest_encoding"><code>hmac.digest()</code></a> methods:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');
hmac.update('some data to hash');
console.log(hmac.digest('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
</code></pre>
<h3>hmac.digest([encoding])<span><a class="mark" href="#crypto_hmac_digest_encoding" id="crypto_hmac_digest_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Calculates the HMAC digest of all of the data passed using <a href="#crypto_hmac_update_data"><code>hmac.update()</code></a>.
The <code>encoding</code> can be <code>'hex'</code>, <code>'binary'</code> or <code>'base64'</code>. If <code>encoding</code> is
provided a string is returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is returned;</p>
<p>The <code>Hmac</code> object can not be used again after <code>hmac.digest()</code> has been
called. Multiple calls to <code>hmac.digest()</code> will result in an error being thrown.</p>
<h3>hmac.update(data[, input_encoding])<span><a class="mark" href="#crypto_hmac_update_data_input_encoding" id="crypto_hmac_update_data_input_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Updates the <code>Hmac</code> content with the given <code>data</code>, the encoding of which
is given in <code>input_encoding</code> and can be <code>'utf8'</code>, <code>'ascii'</code> or
<code>'binary'</code>. If <code>encoding</code> is not provided, and the <code>data</code> is a string, an
encoding of <code>'utf8'</code> is enforced. If <code>data</code> is a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> then
<code>input_encoding</code> is ignored.</p>
<p>This can be called many times with new data as it is streamed.</p>
<h2>Class: Sign<span><a class="mark" href="#crypto_class_sign" id="crypto_class_sign">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>The <code>Sign</code> Class is a utility for generating signatures. It can be used in one
of two ways:</p>
<ul>
<li>As a writable <a href="stream.html#stream_stream">stream</a>, where data to be signed is written and the
<a href="#crypto_sign_sign_private_key_output_format"><code>sign.sign()</code></a> method is used to generate and return the signature, or</li>
<li>Using the <a href="#crypto_sign_update_data"><code>sign.update()</code></a> and <a href="#crypto_sign_sign_private_key_output_format"><code>sign.sign()</code></a> methods to produce the
signature.</li>
</ul>
<p>The <a href="#crypto_crypto_createsign_algorithm"><code>crypto.createSign()</code></a> method is used to create <code>Sign</code> instances. <code>Sign</code>
objects are not to be created directly using the <code>new</code> keyword.</p>
<p>Example: Using <code>Sign</code> objects as streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const sign = crypto.createSign('RSA-SHA256');
sign.write('some data to sign');
sign.end();
const private_key = getPrivateKeySomehow();
console.log(sign.sign(private_key, 'hex'));
// Prints the calculated signature
</code></pre>
<p>Example: Using the <a href="#crypto_sign_update_data"><code>sign.update()</code></a> and <a href="#crypto_sign_sign_private_key_output_format"><code>sign.sign()</code></a> methods:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const sign = crypto.createSign('RSA-SHA256');
sign.update('some data to sign');
const private_key = getPrivateKeySomehow();
console.log(sign.sign(private_key, 'hex'));
// Prints the calculated signature
</code></pre>
<p>A <code>Sign</code> instance can also be created by just passing in the digest
algorithm name, in which case OpenSSL will infer the full signature algorithm
from the type of the PEM-formatted private key, including algorithms that
do not have directly exposed name constants, e.g. 'ecdsa-with-SHA256'.</p>
<p>Example: signing using ECDSA with SHA256</p>
<pre><code class="lang-js">const crypto = require('crypto');
const sign = crypto.createSign('sha256');
sign.update('some data to sign');
const private_key = '-----BEGIN EC PRIVATE KEY-----\n' +
'MHcCAQEEIF+jnWY1D5kbVYDNvxxo/Y+ku2uJPDwS0r/VuPZQrjjVoAoGCCqGSM49\n' +
'AwEHoUQDQgAEurOxfSxmqIRYzJVagdZfMMSjRNNhB8i3mXyIMq704m2m52FdfKZ2\n' +
'pQhByd5eyj3lgZ7m7jbchtdgyOF8Io/1ng==\n' +
'-----END EC PRIVATE KEY-----\n';
console.log(sign.sign(private_key).toString('hex'));
</code></pre>
<h3>sign.sign(private_key[, output_format])<span><a class="mark" href="#crypto_sign_sign_private_key_output_format" id="crypto_sign_sign_private_key_output_format">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Calculates the signature on all the data passed through using either
<a href="#crypto_sign_update_data"><code>sign.update()</code></a> or <a href="stream.html#stream_writable_write_chunk_encoding_callback"><code>sign.write()</code></a>.</p>
<p>The <code>private_key</code> argument can be an object or a string. If <code>private_key</code> is a
string, it is treated as a raw key with no passphrase. If <code>private_key</code> is an
object, it is interpreted as a hash containing two properties:</p>
<ul>
<li><code>key</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - PEM encoded private key</li>
<li><code>passphrase</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - passphrase for the private key</li>
</ul>
<p>The <code>output_format</code> can specify one of <code>'binary'</code>, <code>'hex'</code> or <code>'base64'</code>. If
<code>output_format</code> is provided a string is returned; otherwise a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is
returned.</p>
<p>The <code>Sign</code> object can not be again used after <code>sign.sign()</code> method has been
called. Multiple calls to <code>sign.sign()</code> will result in an error being thrown.</p>
<h3>sign.update(data[, input_encoding])<span><a class="mark" href="#crypto_sign_update_data_input_encoding" id="crypto_sign_update_data_input_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Updates the <code>Sign</code> content with the given <code>data</code>, the encoding of which
is given in <code>input_encoding</code> and can be <code>'utf8'</code>, <code>'ascii'</code> or
<code>'binary'</code>. If <code>encoding</code> is not provided, and the <code>data</code> is a string, an
encoding of <code>'utf8'</code> is enforced. If <code>data</code> is a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> then
<code>input_encoding</code> is ignored.</p>
<p>This can be called many times with new data as it is streamed.</p>
<h2>Class: Verify<span><a class="mark" href="#crypto_class_verify" id="crypto_class_verify">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>The <code>Verify</code> class is a utility for verifying signatures. It can be used in one
of two ways:</p>
<ul>
<li>As a writable <a href="stream.html#stream_stream">stream</a> where written data is used to validate against the
supplied signature, or</li>
<li>Using the <a href="#crypto_verifier_update_data"><code>verify.update()</code></a> and <a href="#crypto_verifier_verify_object_signature_signature_format"><code>verify.verify()</code></a> methods to verify
the signature.</li>
</ul>
<p>The [<code>crypto.createVerify()</code>][] method is used to create <code>Verify</code> instances.
<code>Verify</code> objects are not to be created directly using the <code>new</code> keyword.</p>
<p>Example: Using <code>Verify</code> objects as streams:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const verify = crypto.createVerify('RSA-SHA256');
verify.write('some data to sign');
verify.end();
const public_key = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(public_key, signature));
// Prints true or false
</code></pre>
<p>Example: Using the <a href="#crypto_verifier_update_data"><code>verify.update()</code></a> and <a href="#crypto_verifier_verify_object_signature_signature_format"><code>verify.verify()</code></a> methods:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const verify = crypto.createVerify('RSA-SHA256');
verify.update('some data to sign');
const public_key = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(public_key, signature));
// Prints true or false
</code></pre>
<h3>verifier.update(data[, input_encoding])<span><a class="mark" href="#crypto_verifier_update_data_input_encoding" id="crypto_verifier_update_data_input_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Updates the <code>Verify</code> content with the given <code>data</code>, the encoding of which
is given in <code>input_encoding</code> and can be <code>'utf8'</code>, <code>'ascii'</code> or
<code>'binary'</code>. If <code>encoding</code> is not provided, and the <code>data</code> is a string, an
encoding of <code>'utf8'</code> is enforced. If <code>data</code> is a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> then
<code>input_encoding</code> is ignored.</p>
<p>This can be called many times with new data as it is streamed.</p>
<h3>verifier.verify(object, signature[, signature_format])<span><a class="mark" href="#crypto_verifier_verify_object_signature_signature_format" id="crypto_verifier_verify_object_signature_signature_format">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Verifies the provided data using the given <code>object</code> and <code>signature</code>.
The <code>object</code> argument is a string containing a PEM encoded object, which can be
one an RSA public key, a DSA public key, or an X.509 certificate.
The <code>signature</code> argument is the previously calculated signature for the data, in
the <code>signature_format</code> which can be <code>'binary'</code>, <code>'hex'</code> or <code>'base64'</code>.
If a <code>signature_format</code> is specified, the <code>signature</code> is expected to be a
string; otherwise <code>signature</code> is expected to be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<p>Returns <code>true</code> or <code>false</code> depending on the validity of the signature for
the data and public key.</p>
<p>The <code>verifier</code> object can not be used again after <code>verify.verify()</code> has been
called. Multiple calls to <code>verify.verify()</code> will result in an error being
thrown.</p>
<h2><code>crypto</code> module methods and properties<span><a class="mark" href="#crypto_crypto_module_methods_and_properties" id="crypto_crypto_module_methods_and_properties">#</a></span></h2>
<h3>crypto.DEFAULT_ENCODING<span><a class="mark" href="#crypto_crypto_default_encoding" id="crypto_crypto_default_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.3</span>
</div><p>The default encoding to use for functions that can take either strings
or <a href="buffer.html#buffer_buffer">buffers</a>. The default value is <code>'buffer'</code>, which makes methods
default to <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> objects.</p>
<p>The <code>crypto.DEFAULT_ENCODING</code> mechanism is provided for backwards compatibility
with legacy programs that expect <code>'binary'</code> to be the default encoding.</p>
<p>New applications should expect the default to be <code>'buffer'</code>. This property may
become deprecated in a future Node.js release.</p>
<h3>crypto.createCipher(algorithm, password)<span><a class="mark" href="#crypto_crypto_createcipher_algorithm_password" id="crypto_crypto_createcipher_algorithm_password">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Creates and returns a <code>Cipher</code> object that uses the given <code>algorithm</code> and
<code>password</code>.</p>
<p>The <code>algorithm</code> is dependent on OpenSSL, examples are <code>'aes192'</code>, etc. On
recent OpenSSL releases, <code>openssl list-cipher-algorithms</code> will display the
available cipher algorithms.</p>
<p>The <code>password</code> is used to derive the cipher key and initialization vector (IV).
The value must be either a <code>'binary'</code> encoded string or a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<p>The implementation of <code>crypto.createCipher()</code> derives keys using the OpenSSL
function <a href="https://www.openssl.org/docs/crypto/EVP_BytesToKey.html"><code>EVP_BytesToKey</code></a> with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.</p>
<p>In line with OpenSSL's recommendation to use pbkdf2 instead of
<a href="https://www.openssl.org/docs/crypto/EVP_BytesToKey.html"><code>EVP_BytesToKey</code></a> it is recommended that developers derive a key and IV on
their own using <a href="#crypto_crypto_pbkdf2_password_salt_iterations_keylen_digest_callback"><code>crypto.pbkdf2()</code></a> and to use <a href="#crypto_crypto_createcipheriv_algorithm_key_iv"><code>crypto.createCipheriv()</code></a>
to create the <code>Cipher</code> object.</p>
<h3>crypto.createCipheriv(algorithm, key, iv)<span><a class="mark" href="#crypto_crypto_createcipheriv_algorithm_key_iv" id="crypto_crypto_createcipheriv_algorithm_key_iv">#</a></span></h3>
<p>Creates and returns a <code>Cipher</code> object, with the given <code>algorithm</code>, <code>key</code> and
initialization vector (<code>iv</code>).</p>
<p>The <code>algorithm</code> is dependent on OpenSSL, examples are <code>'aes192'</code>, etc. On
recent OpenSSL releases, <code>openssl list-cipher-algorithms</code> will display the
available cipher algorithms.</p>
<p>The <code>key</code> is the raw key used by the <code>algorithm</code> and <code>iv</code> is an
<a href="https://en.wikipedia.org/wiki/Initialization_vector">initialization vector</a>. Both arguments must be <code>'binary'</code> encoded strings or
<a href="buffer.html#buffer_buffer">buffers</a>.</p>
<h3>crypto.createCredentials(details)<span><a class="mark" href="#crypto_crypto_createcredentials_details" id="crypto_crypto_createcredentials_details">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
<span>Deprecated since: v0.11.13 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="#tls_tls_createsecurecontext_details"><code>tls.createSecureContext()</code></a> instead.</pre><p>The <code>crypto.createCredentials()</code> method is a deprecated alias for creating
and returning a <code>tls.SecureContext</code> object. The <code>crypto.createCredentials()</code>
method should not be used.</p>
<p>The optional <code>details</code> argument is a hash object with keys:</p>
<ul>
<li><code>pfx</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> - PFX or PKCS12 encoded private
key, certificate and CA certificates</li>
<li><code>key</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - PEM encoded private key</li>
<li><code>passphrase</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - passphrase for the private key or PFX</li>
<li><code>cert</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - PEM encoded certificate</li>
<li><code>ca</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> - Either a string or array of strings of PEM encoded CA
certificates to trust.</li>
<li><code>crl</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> - Either a string or array of strings of PEM encoded CRLs
(Certificate Revocation List)</li>
<li><code>ciphers</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> using the <a href="https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT">OpenSSL cipher list format</a> describing the
cipher algorithms to use or exclude.</li>
</ul>
<p>If no 'ca' details are given, Node.js will use Mozilla's default
<a href="https://mxr.mozilla.org/mozilla/source/security/nss/lib/ckfw/builtins/certdata.txt">publicly trusted list of CAs</a>.</p>
<h3>crypto.createDecipher(algorithm, password)<span><a class="mark" href="#crypto_crypto_createdecipher_algorithm_password" id="crypto_crypto_createdecipher_algorithm_password">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Creates and returns a <code>Decipher</code> object that uses the given <code>algorithm</code> and
<code>password</code> (key).</p>
<p>The implementation of <code>crypto.createDecipher()</code> derives keys using the OpenSSL
function <a href="https://www.openssl.org/docs/crypto/EVP_BytesToKey.html"><code>EVP_BytesToKey</code></a> with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.</p>
<p>In line with OpenSSL's recommendation to use pbkdf2 instead of
<a href="https://www.openssl.org/docs/crypto/EVP_BytesToKey.html"><code>EVP_BytesToKey</code></a> it is recommended that developers derive a key and IV on
their own using <a href="#crypto_crypto_pbkdf2_password_salt_iterations_keylen_digest_callback"><code>crypto.pbkdf2()</code></a> and to use <a href="#crypto_crypto_createdecipheriv_algorithm_key_iv"><code>crypto.createDecipheriv()</code></a>
to create the <code>Decipher</code> object.</p>
<h3>crypto.createDecipheriv(algorithm, key, iv)<span><a class="mark" href="#crypto_crypto_createdecipheriv_algorithm_key_iv" id="crypto_crypto_createdecipheriv_algorithm_key_iv">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Creates and returns a <code>Decipher</code> object that uses the given <code>algorithm</code>, <code>key</code>
and initialization vector (<code>iv</code>).</p>
<p>The <code>algorithm</code> is dependent on OpenSSL, examples are <code>'aes192'</code>, etc. On
recent OpenSSL releases, <code>openssl list-cipher-algorithms</code> will display the
available cipher algorithms.</p>
<p>The <code>key</code> is the raw key used by the <code>algorithm</code> and <code>iv</code> is an
<a href="https://en.wikipedia.org/wiki/Initialization_vector">initialization vector</a>. Both arguments must be <code>'binary'</code> encoded strings or
<a href="buffer.html#buffer_buffer">buffers</a>.</p>
<h3>crypto.createDiffieHellman(prime[, prime_encoding][, generator][, generator_encoding])<span><a class="mark" href="#crypto_crypto_creatediffiehellman_prime_prime_encoding_generator_generator_encoding" id="crypto_crypto_creatediffiehellman_prime_prime_encoding_generator_generator_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>Creates a <code>DiffieHellman</code> key exchange object using the supplied <code>prime</code> and an
optional specific <code>generator</code>.</p>
<p>The <code>generator</code> argument can be a number, string, or <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>. If
<code>generator</code> is not specified, the value <code>2</code> is used.</p>
<p>The <code>prime_encoding</code> and <code>generator_encoding</code> arguments can be <code>'binary'</code>,
<code>'hex'</code>, or <code>'base64'</code>.</p>
<p>If <code>prime_encoding</code> is specified, <code>prime</code> is expected to be a string; otherwise
a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is expected.</p>
<p>If <code>generator_encoding</code> is specified, <code>generator</code> is expected to be a string;
otherwise either a number or <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> is expected.</p>
<h3>crypto.createDiffieHellman(prime_length[, generator])<span><a class="mark" href="#crypto_crypto_creatediffiehellman_prime_length_generator" id="crypto_crypto_creatediffiehellman_prime_length_generator">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Creates a <code>DiffieHellman</code> key exchange object and generates a prime of
<code>prime_length</code> bits using an optional specific numeric <code>generator</code>.
If <code>generator</code> is not specified, the value <code>2</code> is used.</p>
<h3>crypto.createECDH(curve_name)<span><a class="mark" href="#crypto_crypto_createecdh_curve_name" id="crypto_crypto_createecdh_curve_name">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Creates an Elliptic Curve Diffie-Hellman (<code>ECDH</code>) key exchange object using a
predefined curve specified by the <code>curve_name</code> string. Use
<a href="crypto.html#crypto_crypto_getcurves"><code>crypto.getCurves()</code></a> to obtain a list of available curve names. On recent
OpenSSL releases, <code>openssl ecparam -list_curves</code> will also display the name
and description of each available elliptic curve.</p>
<h3>crypto.createHash(algorithm)<span><a class="mark" href="#crypto_crypto_createhash_algorithm" id="crypto_crypto_createhash_algorithm">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Creates and returns a <code>Hash</code> object that can be used to generate hash digests
using the given <code>algorithm</code>.</p>
<p>The <code>algorithm</code> is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are <code>'sha256'</code>, <code>'sha512'</code>, etc.
On recent releases of OpenSSL, <code>openssl list-message-digest-algorithms</code> will
display the available digest algorithms.</p>
<p>Example: generating the sha256 sum of a file</p>
<pre><code class="lang-js">const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');
const input = fs.createReadStream(filename);
input.on('readable', () => {
var data = input.read();
if (data)
hash.update(data);
else {
console.log(`${hash.digest('hex')} ${filename}`);
}
});
</code></pre>
<h3>crypto.createHmac(algorithm, key)<span><a class="mark" href="#crypto_crypto_createhmac_algorithm_key" id="crypto_crypto_createhmac_algorithm_key">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p>Creates and returns an <code>Hmac</code> object that uses the given <code>algorithm</code> and <code>key</code>.</p>
<p>The <code>algorithm</code> is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are <code>'sha256'</code>, <code>'sha512'</code>, etc.
On recent releases of OpenSSL, <code>openssl list-message-digest-algorithms</code> will
display the available digest algorithms.</p>
<p>The <code>key</code> is the HMAC key used to generate the cryptographic HMAC hash.</p>
<p>Example: generating the sha256 HMAC of a file</p>
<pre><code class="lang-js">const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');
const input = fs.createReadStream(filename);
input.on('readable', () => {
var data = input.read();
if (data)
hmac.update(data);
else {
console.log(`${hmac.digest('hex')} ${filename}`);
}
});
</code></pre>
<h3>crypto.createSign(algorithm)<span><a class="mark" href="#crypto_crypto_createsign_algorithm" id="crypto_crypto_createsign_algorithm">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Creates and returns a <code>Sign</code> object that uses the given <code>algorithm</code>.
Use <a href="#crypto_crypto_gethashes"><code>crypto.getHashes()</code></a> to obtain an array of names of the available
signing algorithms.</p>
<h3>crypto.createVerify(algorithm)<span><a class="mark" href="#crypto_crypto_createverify_algorithm" id="crypto_crypto_createverify_algorithm">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Creates and returns a <code>Verify</code> object that uses the given algorithm.
Use <a href="#crypto_crypto_gethashes"><code>crypto.getHashes()</code></a> to obtain an array of names of the available
signing algorithms.</p>
<h3>crypto.getCiphers()<span><a class="mark" href="#crypto_crypto_getciphers" id="crypto_crypto_getciphers">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.3</span>
</div><p>Returns an array with the names of the supported cipher algorithms.</p>
<p>Example:</p>
<pre><code class="lang-js">const ciphers = crypto.getCiphers();
console.log(ciphers); // ['aes-128-cbc', 'aes-128-ccm', ...]
</code></pre>
<h3>crypto.getCurves()<span><a class="mark" href="#crypto_crypto_getcurves" id="crypto_crypto_getcurves">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v2.3.0</span>
</div><p>Returns an array with the names of the supported elliptic curves.</p>
<p>Example:</p>
<pre><code class="lang-js">const curves = crypto.getCurves();
console.log(curves); // ['secp256k1', 'secp384r1', ...]
</code></pre>
<h3>crypto.getDiffieHellman(group_name)<span><a class="mark" href="#crypto_crypto_getdiffiehellman_group_name" id="crypto_crypto_getdiffiehellman_group_name">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.5</span>
</div><p>Creates a predefined <code>DiffieHellman</code> key exchange object. The
supported groups are: <code>'modp1'</code>, <code>'modp2'</code>, <code>'modp5'</code> (defined in
<a href="https://www.rfc-editor.org/rfc/rfc2412.txt">RFC 2412</a>, but see <a href="#fs_caveats">Caveats</a>) and <code>'modp14'</code>, <code>'modp15'</code>,
<code>'modp16'</code>, <code>'modp17'</code>, <code>'modp18'</code> (defined in <a href="https://www.rfc-editor.org/rfc/rfc3526.txt">RFC 3526</a>). The
returned object mimics the interface of objects created by
<a href="#crypto_crypto_creatediffiehellman_prime_prime_encoding_generator_generator_encoding"><code>crypto.createDiffieHellman()</code></a>, but will not allow changing
the keys (with <a href="#crypto_diffiehellman_setpublickey_public_key_encoding"><code>diffieHellman.setPublicKey()</code></a> for example). The
advantage of using this method is that the parties do not have to
generate nor exchange a group modulus beforehand, saving both processor
and communication time.</p>
<p>Example (obtaining a shared secret):</p>
<pre><code class="lang-js">const crypto = require('crypto');
const alice = crypto.getDiffieHellman('modp14');
const bob = crypto.getDiffieHellman('modp14');
alice.generateKeys();
bob.generateKeys();
const alice_secret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bob_secret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
/* alice_secret and bob_secret should be the same */
console.log(alice_secret == bob_secret);
</code></pre>
<h3>crypto.getHashes()<span><a class="mark" href="#crypto_crypto_gethashes" id="crypto_crypto_gethashes">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.3</span>
</div><p>Returns an array of the names of the supported hash algorithms,
such as <code>RSA-SHA256</code>.</p>
<p>Example:</p>
<pre><code class="lang-js">const hashes = crypto.getHashes();
console.log(hashes); // ['sha', 'sha1', 'sha1WithRSAEncryption', ...]
</code></pre>
<h3>crypto.pbkdf2(password, salt, iterations, keylen[, digest], callback)<span><a class="mark" href="#crypto_crypto_pbkdf2_password_salt_iterations_keylen_digest_callback" id="crypto_crypto_pbkdf2_password_salt_iterations_keylen_digest_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.5</span>
</div><p>Provides an asynchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by <code>digest</code> is
applied to derive a key of the requested byte length (<code>keylen</code>) from the
<code>password</code>, <code>salt</code> and <code>iterations</code>. If the <code>digest</code> algorithm is not specified,
a default of <code>'sha1'</code> is used.</p>
<p>The supplied <code>callback</code> function is called with two arguments: <code>err</code> and
<code>derivedKey</code>. If an error occurs, <code>err</code> will be set; otherwise <code>err</code> will be
null. The successfully generated <code>derivedKey</code> will be passed as a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<p>The <code>iterations</code> argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.</p>
<p>The <code>salt</code> should also be as unique as possible. It is recommended that the
salts are random and their lengths are greater than 16 bytes. See
<a href="http://csrc.nist.gov/publications/nistpubs/800-132/nist-sp800-132.pdf">NIST SP 800-132</a> for details.</p>
<p>Example:</p>
<pre><code class="lang-js">const crypto = require('crypto');
crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', (err, key) => {
if (err) throw err;
console.log(key.toString('hex')); // 'c5e478d...1469e50'
});
</code></pre>
<p>An array of supported digest functions can be retrieved using
<a href="#crypto_crypto_gethashes"><code>crypto.getHashes()</code></a>.</p>
<h3>crypto.pbkdf2Sync(password, salt, iterations, keylen[, digest])<span><a class="mark" href="#crypto_crypto_pbkdf2sync_password_salt_iterations_keylen_digest" id="crypto_crypto_pbkdf2sync_password_salt_iterations_keylen_digest">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.3</span>
</div><p>Provides a synchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by <code>digest</code> is
applied to derive a key of the requested byte length (<code>keylen</code>) from the
<code>password</code>, <code>salt</code> and <code>iterations</code>. If the <code>digest</code> algorithm is not specified,
a default of <code>'sha1'</code> is used.</p>
<p>If an error occurs an Error will be thrown, otherwise the derived key will be
returned as a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<p>The <code>iterations</code> argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.</p>
<p>The <code>salt</code> should also be as unique as possible. It is recommended that the
salts are random and their lengths are greater than 16 bytes. See
<a href="http://csrc.nist.gov/publications/nistpubs/800-132/nist-sp800-132.pdf">NIST SP 800-132</a> for details.</p>
<p>Example:</p>
<pre><code class="lang-js">const crypto = require('crypto');
const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 512, 'sha512');
console.log(key.toString('hex')); // 'c5e478d...1469e50'
</code></pre>
<p>An array of supported digest functions can be retrieved using
<a href="#crypto_crypto_gethashes"><code>crypto.getHashes()</code></a>.</p>
<h3>crypto.privateDecrypt(private_key, buffer)<span><a class="mark" href="#crypto_crypto_privatedecrypt_private_key_buffer" id="crypto_crypto_privatedecrypt_private_key_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Decrypts <code>buffer</code> with <code>private_key</code>.</p>
<p><code>private_key</code> can be an object or a string. If <code>private_key</code> is a string, it is
treated as the key with no passphrase and will use <code>RSA_PKCS1_OAEP_PADDING</code>.
If <code>private_key</code> is an object, it is interpreted as a hash object with the
keys:</p>
<ul>
<li><code>key</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - PEM encoded private key</li>
<li><code>passphrase</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - Optional passphrase for the private key</li>
<li><code>padding</code> : An optional padding value, one of the following:<ul>
<li><code>constants.RSA_NO_PADDING</code></li>
<li><code>constants.RSA_PKCS1_PADDING</code></li>
<li><code>constants.RSA_PKCS1_OAEP_PADDING</code></li>
</ul>
</li>
</ul>
<p>All paddings are defined in the <code>constants</code> module.</p>
<h3>crypto.privateEncrypt(private_key, buffer)<span><a class="mark" href="#crypto_crypto_privateencrypt_private_key_buffer" id="crypto_crypto_privateencrypt_private_key_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.1.0</span>
</div><p>Encrypts <code>buffer</code> with <code>private_key</code>.</p>
<p><code>private_key</code> can be an object or a string. If <code>private_key</code> is a string, it is
treated as the key with no passphrase and will use <code>RSA_PKCS1_PADDING</code>.
If <code>private_key</code> is an object, it is interpreted as a hash object with the
keys:</p>
<ul>
<li><code>key</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - PEM encoded private key</li>
<li><code>passphrase</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - Optional passphrase for the private key</li>
<li><code>padding</code> : An optional padding value, one of the following:<ul>
<li><code>constants.RSA_NO_PADDING</code></li>
<li><code>constants.RSA_PKCS1_PADDING</code></li>
</ul>
</li>
</ul>
<p>All paddings are defined in the <code>constants</code> module.</p>
<h3>crypto.publicDecrypt(public_key, buffer)<span><a class="mark" href="#crypto_crypto_publicdecrypt_public_key_buffer" id="crypto_crypto_publicdecrypt_public_key_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.1.0</span>
</div><p>Decrypts <code>buffer</code> with <code>public_key</code>.</p>
<p><code>public_key</code> can be an object or a string. If <code>public_key</code> is a string, it is
treated as the key with no passphrase and will use <code>RSA_PKCS1_PADDING</code>.
If <code>public_key</code> is an object, it is interpreted as a hash object with the
keys:</p>
<ul>
<li><code>key</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - PEM encoded public key</li>
<li><code>passphrase</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - Optional passphrase for the private key</li>
<li><code>padding</code> : An optional padding value, one of the following:<ul>
<li><code>constants.RSA_NO_PADDING</code></li>
<li><code>constants.RSA_PKCS1_PADDING</code></li>
<li><code>constants.RSA_PKCS1_OAEP_PADDING</code></li>
</ul>
</li>
</ul>
<p>Because RSA public keys can be derived from private keys, a private key may
be passed instead of a public key.</p>
<p>All paddings are defined in the <code>constants</code> module.</p>
<h3>crypto.publicEncrypt(public_key, buffer)<span><a class="mark" href="#crypto_crypto_publicencrypt_public_key_buffer" id="crypto_crypto_publicencrypt_public_key_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Encrypts <code>buffer</code> with <code>public_key</code>.</p>
<p><code>public_key</code> can be an object or a string. If <code>public_key</code> is a string, it is
treated as the key with no passphrase and will use <code>RSA_PKCS1_OAEP_PADDING</code>.
If <code>public_key</code> is an object, it is interpreted as a hash object with the
keys:</p>
<ul>
<li><code>key</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - PEM encoded public key</li>
<li><code>passphrase</code> : <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - Optional passphrase for the private key</li>
<li><code>padding</code> : An optional padding value, one of the following:<ul>
<li><code>constants.RSA_NO_PADDING</code></li>
<li><code>constants.RSA_PKCS1_PADDING</code></li>
<li><code>constants.RSA_PKCS1_OAEP_PADDING</code></li>
</ul>
</li>
</ul>
<p>Because RSA public keys can be derived from private keys, a private key may
be passed instead of a public key.</p>
<p>All paddings are defined in the <code>constants</code> module.</p>
<h3>crypto.randomBytes(size[, callback])<span><a class="mark" href="#crypto_crypto_randombytes_size_callback" id="crypto_crypto_randombytes_size_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Generates cryptographically strong pseudo-random data. The <code>size</code> argument
is a number indicating the number of bytes to generate.</p>
<p>If a <code>callback</code> function is provided, the bytes are generated asynchronously
and the <code>callback</code> function is invoked with two arguments: <code>err</code> and <code>buf</code>.
If an error occurs, <code>err</code> will be an Error object; otherwise it is null. The
<code>buf</code> argument is a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> containing the generated bytes.</p>
<pre><code class="lang-js">// Asynchronous
const crypto = require('crypto');
crypto.randomBytes(256, (err, buf) => {
if (err) throw err;
console.log(`${buf.length} bytes of random data: ${buf.toString('hex')}`);
});
</code></pre>
<p>If the <code>callback</code> function is not provided, the random bytes are generated
synchronously and returned as a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>. An error will be thrown if
there is a problem generating the bytes.</p>
<pre><code class="lang-js">// Synchronous
const buf = crypto.randomBytes(256);
console.log(
`${buf.length} bytes of random data: ${buf.toString('hex')}`);
</code></pre>
<p>The <code>crypto.randomBytes()</code> method will block until there is sufficient entropy.
This should normally never take longer than a few milliseconds. The only time
when generating the random bytes may conceivably block for a longer period of
time is right after boot, when the whole system is still low on entropy.</p>
<h3>crypto.setEngine(engine[, flags])<span><a class="mark" href="#crypto_crypto_setengine_engine_flags" id="crypto_crypto_setengine_engine_flags">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.11</span>
</div><p>Load and set the <code>engine</code> for some or all OpenSSL functions (selected by flags).</p>
<p><code>engine</code> could be either an id or a path to the engine's shared library.</p>
<p>The optional <code>flags</code> argument uses <code>ENGINE_METHOD_ALL</code> by default. The <code>flags</code>
is a bit field taking one of or a mix of the following flags (defined in the
<code>constants</code> module):</p>
<ul>
<li><code>ENGINE_METHOD_RSA</code></li>
<li><code>ENGINE_METHOD_DSA</code></li>
<li><code>ENGINE_METHOD_DH</code></li>
<li><code>ENGINE_METHOD_RAND</code></li>
<li><code>ENGINE_METHOD_ECDH</code></li>
<li><code>ENGINE_METHOD_ECDSA</code></li>
<li><code>ENGINE_METHOD_CIPHERS</code></li>
<li><code>ENGINE_METHOD_DIGESTS</code></li>
<li><code>ENGINE_METHOD_STORE</code></li>
<li><code>ENGINE_METHOD_PKEY_METH</code></li>
<li><code>ENGINE_METHOD_PKEY_ASN1_METH</code></li>
<li><code>ENGINE_METHOD_ALL</code></li>
<li><code>ENGINE_METHOD_NONE</code></li>
</ul>
<h2>Notes<span><a class="mark" href="#crypto_notes" id="crypto_notes">#</a></span></h2>
<h3>Legacy Streams API (pre Node.js v0.10)<span><a class="mark" href="#crypto_legacy_streams_api_pre_node_js_v0_10" id="crypto_legacy_streams_api_pre_node_js_v0_10">#</a></span></h3>
<p>The Crypto module was added to Node.js before there was the concept of a
unified Stream API, and before there were <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> objects for handling
binary data. As such, the many of the <code>crypto</code> defined classes have methods not
typically found on other Node.js classes that implement the <a href="stream.html#stream_stream">streams</a>
API (e.g. <code>update()</code>, <code>final()</code>, or <code>digest()</code>). Also, many methods accepted
and returned <code>'binary'</code> encoded strings by default rather than Buffers. This
default was changed after Node.js v0.8 to use <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> objects by default
instead.</p>
<h3>Recent ECDH Changes<span><a class="mark" href="#crypto_recent_ecdh_changes" id="crypto_recent_ecdh_changes">#</a></span></h3>
<p>Usage of <code>ECDH</code> with non-dynamically generated key pairs has been simplified.
Now, <a href="#crypto_ecdh_setprivatekey_private_key_encoding"><code>ecdh.setPrivateKey()</code></a> can be called with a preselected private key
and the associated public point (key) will be computed and stored in the object.
This allows code to only store and provide the private part of the EC key pair.
<a href="#crypto_ecdh_setprivatekey_private_key_encoding"><code>ecdh.setPrivateKey()</code></a> now also validates that the private key is valid for
the selected curve.</p>
<p>The <a href="#crypto_ecdh_setpublickey_public_key_encoding"><code>ecdh.setPublicKey()</code></a> method is now deprecated as its inclusion in the
API is not useful. Either a previously stored private key should be set, which
automatically generates the associated public key, or <a href="#crypto_ecdh_generatekeys_encoding_format"><code>ecdh.generateKeys()</code></a>
should be called. The main drawback of using <a href="#crypto_ecdh_setpublickey_public_key_encoding"><code>ecdh.setPublicKey()</code></a> is that
it can be used to put the ECDH key pair into an inconsistent state.</p>
<h3>Support for weak or compromised algorithms<span><a class="mark" href="#crypto_support_for_weak_or_compromised_algorithms" id="crypto_support_for_weak_or_compromised_algorithms">#</a></span></h3>
<p>The <code>crypto</code> module still supports some algorithms which are already
compromised and are not currently recommended for use. The API also allows
the use of ciphers and hashes with a small key size that are considered to be
too weak for safe use.</p>
<p>Users should take full responsibility for selecting the crypto
algorithm and key size according to their security requirements.</p>
<p>Based on the recommendations of <a href="http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-131Ar1.pdf">NIST SP 800-131A</a>:</p>
<ul>
<li>MD5 and SHA-1 are no longer acceptable where collision resistance is
required such as digital signatures.</li>
<li>The key used with RSA, DSA and DH algorithms is recommended to have
at least 2048 bits and that of the curve of ECDSA and ECDH at least
224 bits, to be safe to use for several years.</li>
<li>The DH groups of <code>modp1</code>, <code>modp2</code> and <code>modp5</code> have a key size
smaller than 2048 bits and are not recommended.</li>
</ul>
<p>See the reference for other recommendations and details.</p>
<!-- [end-include:crypto.md] -->
<!-- [start-include:debugger.md] -->
<h1>Debugger<span><a class="mark" href="#debugger_debugger" id="debugger_debugger">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><!-- type=misc -->
<p>Node.js includes an out-of-process debugging utility accessible via a
<a href="https://github.com/v8/v8/wiki/Debugging-Protocol">TCP-based protocol</a> and built-in debugging client. To use it, start Node.js
with the <code>debug</code> argument followed by the path to the script to debug; a prompt
will be displayed indicating successful launch of the debugger:</p>
<pre><code>$ node debug myscript.js
< debugger listening on port 5858
connecting... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
1 x = 5;
2 setTimeout(() => {
3 debugger;
debug>
</code></pre><p>Node.js's debugger client is not a full-featured debugger, but simple step and
inspection are possible.</p>
<p>Inserting the statement <code>debugger;</code> into the source code of a script will
enable a breakpoint at that position in the code:</p>
<pre><code class="lang-js">// myscript.js
x = 5;
setTimeout(() => {
debugger;
console.log('world');
}, 1000);
console.log('hello');
</code></pre>
<p>Once the debugger is run, a breakpoint will occur at line 4:</p>
<pre><code>$ node debug myscript.js
< debugger listening on port 5858
connecting... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
1 x = 5;
2 setTimeout(() => {
3 debugger;
debug> cont
< hello
break in /home/indutny/Code/git/indutny/myscript.js:3
1 x = 5;
2 setTimeout(() => {
3 debugger;
4 console.log('world');
5 }, 1000);
debug> next
break in /home/indutny/Code/git/indutny/myscript.js:4
2 setTimeout(() => {
3 debugger;
4 console.log('world');
5 }, 1000);
6 console.log('hello');
debug> repl
Press Ctrl + C to leave debug repl
> x
5
> 2+2
4
debug> next
< world
break in /home/indutny/Code/git/indutny/myscript.js:5
3 debugger;
4 console.log('world');
5 }, 1000);
6 console.log('hello');
7
debug> quit
</code></pre><p>The <code>repl</code> command allows code to be evaluated remotely. The <code>next</code> command
steps to the next line. Type <code>help</code> to see what other commands are available.</p>
<h2>Watchers<span><a class="mark" href="#debugger_watchers" id="debugger_watchers">#</a></span></h2>
<p>It is possible to watch expression and variable values while debugging. On
every breakpoint, each expression from the watchers list will be evaluated
in the current context and displayed immediately before the breakpoint's
source code listing.</p>
<p>To begin watching an expression, type <code>watch('my_expression')</code>. The command
<code>watchers</code> will print the active watchers. To remove a watcher, type
<code>unwatch('my_expression')</code>.</p>
<h2>Command reference<span><a class="mark" href="#debugger_command_reference" id="debugger_command_reference">#</a></span></h2>
<h3>Stepping<span><a class="mark" href="#debugger_stepping" id="debugger_stepping">#</a></span></h3>
<div class="signature"><ul>
<li><code>cont</code>, <code>c</code> - Continue execution</li>
<li><code>next</code>, <code>n</code> - Step next</li>
<li><code>step</code>, <code>s</code> - Step in</li>
<li><code>out</code>, <code>o</code> - Step out</li>
<li><code>pause</code> - Pause running code (like pause button in Developer Tools)</li>
</ul>
</div><h3>Breakpoints<span><a class="mark" href="#debugger_breakpoints" id="debugger_breakpoints">#</a></span></h3>
<div class="signature"><ul>
<li><code>setBreakpoint()</code>, <code>sb()</code> - Set breakpoint on current line</li>
<li><code>setBreakpoint(line)</code>, <code>sb(line)</code> - Set breakpoint on specific line</li>
<li><code>setBreakpoint('fn()')</code>, <code>sb(...)</code> - Set breakpoint on a first statement in
functions body</li>
<li><code>setBreakpoint('script.js', 1)</code>, <code>sb(...)</code> - Set breakpoint on first line of
script.js</li>
<li><code>clearBreakpoint('script.js', 1)</code>, <code>cb(...)</code> - Clear breakpoint in script.js
on line 1</li>
</ul>
</div><p>It is also possible to set a breakpoint in a file (module) that
isn't loaded yet:</p>
<pre><code>$ node debug test/fixtures/break-in-module/main.js
< debugger listening on port 5858
connecting to port 5858... ok
break in test/fixtures/break-in-module/main.js:1
1 var mod = require('./mod.js');
2 mod.hello();
3 mod.hello();
debug> setBreakpoint('mod.js', 23)
Warning: script 'mod.js' was not loaded yet.
1 var mod = require('./mod.js');
2 mod.hello();
3 mod.hello();
debug> c
break in test/fixtures/break-in-module/mod.js:23
21
22 exports.hello = () => {
23 return 'hello from module';
24 };
25
debug>
</code></pre><h3>Information<span><a class="mark" href="#debugger_information" id="debugger_information">#</a></span></h3>
<div class="signature"><ul>
<li><code>backtrace</code>, <code>bt</code> - Print backtrace of current execution frame</li>
<li><code>list(5)</code> - List scripts source code with 5 line context (5 lines before and
after)</li>
<li><code>watch(expr)</code> - Add expression to watch list</li>
<li><code>unwatch(expr)</code> - Remove expression from watch list</li>
<li><code>watchers</code> - List all watchers and their values (automatically listed on each
breakpoint)</li>
<li><code>repl</code> - Open debugger's repl for evaluation in debugging script's context</li>
<li><code>exec expr</code> - Execute an expression in debugging script's context</li>
</ul>
</div><h3>Execution control<span><a class="mark" href="#debugger_execution_control" id="debugger_execution_control">#</a></span></h3>
<div class="signature"><ul>
<li><code>run</code> - Run script (automatically runs on debugger's start)</li>
<li><code>restart</code> - Restart script</li>
<li><code>kill</code> - Kill script</li>
</ul>
</div><h3>Various<span><a class="mark" href="#debugger_various" id="debugger_various">#</a></span></h3>
<div class="signature"><ul>
<li><code>scripts</code> - List all loaded scripts</li>
<li><code>version</code> - Display V8's version</li>
</ul>
</div><h2>Advanced Usage<span><a class="mark" href="#debugger_advanced_usage" id="debugger_advanced_usage">#</a></span></h2>
<p>An alternative way of enabling and accessing the debugger is to start
Node.js with the <code>--debug</code> command-line flag or by signaling an existing
Node.js process with <code>SIGUSR1</code>.</p>
<p>Once a process has been set in debug mode this way, it can be inspected
using the Node.js debugger by either connecting to the <code>pid</code> of the running
process or via URI reference to the listening debugger:</p>
<ul>
<li><code>node debug -p <pid></code> - Connects to the process via the <code>pid</code></li>
<li><code>node debug <URI></code> - Connects to the process via the URI such as
localhost:5858</li>
</ul>
<!-- [end-include:debugger.md] -->
<!-- [start-include:dgram.md] -->
<h1>UDP / Datagram Sockets<span><a class="mark" href="#dgram_udp_datagram_sockets" id="dgram_udp_datagram_sockets">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><!-- name=dgram -->
<p>The <code>dgram</code> module provides an implementation of UDP Datagram sockets.</p>
<pre><code class="lang-js">const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
var address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// server listening 0.0.0.0:41234
</code></pre>
<h2>Class: dgram.Socket<span><a class="mark" href="#dgram_class_dgram_socket" id="dgram_class_dgram_socket">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><p>The <code>dgram.Socket</code> object is an <a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a> that encapsulates the
datagram functionality.</p>
<p>New instances of <code>dgram.Socket</code> are created using <a href="#dgram_dgram_createsocket_options_callback"><code>dgram.createSocket()</code></a>.
The <code>new</code> keyword is not to be used to create <code>dgram.Socket</code> instances.</p>
<h3>Event: 'close'<span><a class="mark" href="#dgram_event_close" id="dgram_event_close">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><p>The <code>'close'</code> event is emitted after a socket is closed with <a href="#dgram_socket_close_callback"><code>close()</code></a>.
Once triggered, no new <code>'message'</code> events will be emitted on this socket.</p>
<h3>Event: 'error'<span><a class="mark" href="#dgram_event_error" id="dgram_event_error">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><ul>
<li><code>exception</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>The <code>'error'</code> event is emitted whenever any error occurs. The event handler
function is passed a single Error object.</p>
<h3>Event: 'listening'<span><a class="mark" href="#dgram_event_listening" id="dgram_event_listening">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><p>The <code>'listening'</code> event is emitted whenever a socket begins listening for
datagram messages. This occurs as soon as UDP sockets are created.</p>
<h3>Event: 'message'<span><a class="mark" href="#dgram_event_message" id="dgram_event_message">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><p>The <code>'message'</code> event is emitted when a new datagram is available on a socket.
The event handler function is passed two arguments: <code>msg</code> and <code>rinfo</code>.</p>
<ul>
<li><code>msg</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> - The message</li>
<li><code>rinfo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> - Remote address information<ul>
<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The sender address</li>
<li><code>family</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The address family (<code>'IPv4'</code> or <code>'IPv6'</code>)</li>
<li><code>port</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The sender port</li>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The message size</li>
</ul>
</li>
</ul>
<h3>socket.addMembership(multicastAddress[, multicastInterface])<span><a class="mark" href="#dgram_socket_addmembership_multicastaddress_multicastinterface" id="dgram_socket_addmembership_multicastaddress_multicastinterface">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.9</span>
</div><ul>
<li><code>multicastAddress</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
<li><code>multicastInterface</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a>, Optional</li>
</ul>
<p>Tells the kernel to join a multicast group at the given <code>multicastAddress</code> and
<code>multicastInterface</code> using the <code>IP_ADD_MEMBERSHIP</code> socket option. If the
<code>multicastInterface</code> argument is not specified, the operating system will choose
one interface and will add membership to it. To add membership to every
available interface, call <code>addMembership</code> multiple times, once per interface.</p>
<h3>socket.address()<span><a class="mark" href="#dgram_socket_address" id="dgram_socket_address">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><p>Returns an object containing the address information for a socket.
For UDP sockets, this object will contain <code>address</code>, <code>family</code> and <code>port</code>
properties.</p>
<h3>socket.bind([port][, address][, callback])<span><a class="mark" href="#dgram_socket_bind_port_address_callback" id="dgram_socket_bind_port_address_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><ul>
<li><code>port</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> - Integer, Optional</li>
<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a>, Optional</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> with no parameters, Optional. Called when
binding is complete.</li>
</ul>
<p>For UDP sockets, causes the <code>dgram.Socket</code> to listen for datagram
messages on a named <code>port</code> and optional <code>address</code>. If <code>port</code> is not
specified or is <code>0</code>, the operating system will attempt to bind to a
random port. If <code>address</code> is not specified, the operating system will
attempt to listen on all addresses. Once binding is complete, a
<code>'listening'</code> event is emitted and the optional <code>callback</code> function is
called.</p>
<p>Note that specifying both a <code>'listening'</code> event listener and passing a
<code>callback</code> to the <code>socket.bind()</code> method is not harmful but not very
useful.</p>
<p>A bound datagram socket keeps the Node.js process running to receive
datagram messages.</p>
<p>If binding fails, an <code>'error'</code> event is generated. In rare case (e.g.
attempting to bind with a closed socket), an <a href="errors.html#errors_class_error"><code>Error</code></a> may be thrown.</p>
<p>Example of a UDP server listening on port 41234:</p>
<pre><code class="lang-js">const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
var address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// server listening 0.0.0.0:41234
</code></pre>
<h3>socket.bind(options[, callback])<span><a class="mark" href="#dgram_socket_bind_options_callback" id="dgram_socket_bind_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> - Required. Supports the following properties:<ul>
<li><code>port</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> - Optional.</li>
<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - Optional.</li>
<li><code>exclusive</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> - Optional.</li>
</ul>
</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> - Optional.</li>
</ul>
<p>For UDP sockets, causes the <code>dgram.Socket</code> to listen for datagram
messages on a named <code>port</code> and optional <code>address</code> that are passed as
properties of an <code>options</code> object passed as the first argument. If
<code>port</code> is not specified or is <code>0</code>, the operating system will attempt
to bind to a random port. If <code>address</code> is not specified, the operating
system will attempt to listen on all addresses. Once binding is
complete, a <code>'listening'</code> event is emitted and the optional <code>callback</code>
function is called.</p>
<p>Note that specifying both a <code>'listening'</code> event listener and passing a
<code>callback</code> to the <code>socket.bind()</code> method is not harmful but not very
useful.</p>
<p>The <code>options</code> object may contain an additional <code>exclusive</code> property that is
use when using <code>dgram.Socket</code> objects with the <a href="cluster.html"><code>cluster</code></a> module. When
<code>exclusive</code> is set to <code>false</code> (the default), cluster workers will use the same
underlying socket handle allowing connection handling duties to be shared.
When <code>exclusive</code> is <code>true</code>, however, the handle is not shared and attempted
port sharing results in an error.</p>
<p>A bound datagram socket keeps the Node.js process running to receive
datagram messages.</p>
<p>If binding fails, an <code>'error'</code> event is generated. In rare case (e.g.
attempting to bind with a closed socket), an <a href="errors.html#errors_class_error"><code>Error</code></a> may be thrown.</p>
<p>An example socket listening on an exclusive port is shown below.</p>
<pre><code class="lang-js">socket.bind({
address: 'localhost',
port: 8000,
exclusive: true
});
</code></pre>
<h3>socket.close([callback])<span><a class="mark" href="#dgram_socket_close_callback" id="dgram_socket_close_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><p>Close the underlying socket and stop listening for data on it. If a callback is
provided, it is added as a listener for the <a href="#net_event_close"><code>'close'</code></a> event.</p>
<h3>socket.dropMembership(multicastAddress[, multicastInterface])<span><a class="mark" href="#dgram_socket_dropmembership_multicastaddress_multicastinterface" id="dgram_socket_dropmembership_multicastaddress_multicastinterface">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.9</span>
</div><ul>
<li><code>multicastAddress</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
<li><code>multicastInterface</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a>, Optional</li>
</ul>
<p>Instructs the kernel to leave a multicast group at <code>multicastAddress</code> using the
<code>IP_DROP_MEMBERSHIP</code> socket option. This method is automatically called by the
kernel when the socket is closed or the process terminates, so most apps will
never have reason to call this.</p>
<p>If <code>multicastInterface</code> is not specified, the operating system will attempt to
drop membership on all valid interfaces.</p>
<h3>socket.send(buf, offset, length, port, address[, callback])<span><a class="mark" href="#dgram_socket_send_buf_offset_length_port_address_callback" id="dgram_socket_send_buf_offset_length_port_address_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><ul>
<li><code>buf</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Message to be sent</li>
<li><code>offset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Integer. Offset in the buffer where the message starts.</li>
<li><code>length</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Integer. Number of bytes in the message.</li>
<li><code>port</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Integer. Destination port.</li>
<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Destination hostname or IP address.</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Called when the message has been sent. Optional.</li>
</ul>
<p>Broadcasts a datagram on the socket. The destination <code>port</code> and <code>address</code> must
be specified.</p>
<p>The <code>buf</code> argument is a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> object containing the message. The <code>offset</code>
and <code>length</code> specify the offset within the <code>Buffer</code> where the message begins
and the number of bytes in the message, respectively. With messages that
contain multi-byte characters, <code>offset</code> and <code>length</code> will be calculated with
respect to <a href="buffer.html#buffer_class_method_buffer_bytelength_string_encoding">byte length</a> and not the character position.</p>
<p>The <code>address</code> argument is a string. If the value of <code>address</code> is a host name,
DNS will be used to resolve the address of the host. If the <code>address</code> is not
specified or is an empty string, <code>'0.0.0.0'</code> or <code>'::0'</code> will be used instead.
It is possible, depending on the network configuration, that these defaults
may not work; accordingly, it is best to be explicit about the destination
address.</p>
<p>If the socket has not been previously bound with a call to <code>bind</code>, the socket
is assigned a random port number and is bound to the "all interfaces" address
(<code>'0.0.0.0'</code> for <code>udp4</code> sockets, <code>'::0'</code> for <code>udp6</code> sockets.)</p>
<p>An optional <code>callback</code> function may be specified to as a way of reporting
DNS errors or for determining when it is safe to reuse the <code>buf</code> object.
Note that DNS lookups delay the time to send for at least one tick of the
Node.js event loop.</p>
<p>The only way to know for sure that the datagram has been sent is by using a
<code>callback</code>. If an error occurs and a <code>callback</code> is given, the error will be
passed as the first argument to the <code>callback</code>. If a <code>callback</code> is not given,
the error is emitted as an <code>'error'</code> event on the <code>socket</code> object.</p>
<p>Example of sending a UDP packet to a random port on <code>localhost</code>;</p>
<pre><code class="lang-js">const dgram = require('dgram');
const message = new Buffer('Some bytes');
const client = dgram.createSocket('udp4');
client.send(message, 0, message.length, 41234, 'localhost', (err) => {
client.close();
});
</code></pre>
<p><strong>A Note about UDP datagram size</strong></p>
<p>The maximum size of an <code>IPv4/v6</code> datagram depends on the <code>MTU</code>
(<em>Maximum Transmission Unit</em>) and on the <code>Payload Length</code> field size.</p>
<ul>
<li><p>The <code>Payload Length</code> field is <code>16 bits</code> wide, which means that a normal
payload exceed 64K octets <em>including</em> the internet header and data
(65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header);
this is generally true for loopback interfaces, but such long datagram
messages are impractical for most hosts and networks.</p>
</li>
<li><p>The <code>MTU</code> is the largest size a given link layer technology can support for
datagram messages. For any link, <code>IPv4</code> mandates a minimum <code>MTU</code> of <code>68</code>
octets, while the recommended <code>MTU</code> for IPv4 is <code>576</code> (typically recommended
as the <code>MTU</code> for dial-up type applications), whether they arrive whole or in
fragments.</p>
<p>For <code>IPv6</code>, the minimum <code>MTU</code> is <code>1280</code> octets, however, the mandatory minimum
fragment reassembly buffer size is <code>1500</code> octets. The value of <code>68</code> octets is
very small, since most current link layer technologies, like Ethernet, have a
minimum <code>MTU</code> of <code>1500</code>.</p>
</li>
</ul>
<p>It is impossible to know in advance the MTU of each link through which
a packet might travel. Sending a datagram greater than the receiver <code>MTU</code> will
not work because the packet will get silently dropped without informing the
source that the data did not reach its intended recipient.</p>
<h3>socket.setBroadcast(flag)<span><a class="mark" href="#dgram_socket_setbroadcast_flag" id="dgram_socket_setbroadcast_flag">#</a></span></h3>
<div class="signature"><ul>
<li><code>flag</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
</div><p>Sets or clears the <code>SO_BROADCAST</code> socket option. When set to <code>true</code>, UDP
packets may be sent to a local interface's broadcast address.</p>
<h3>socket.setMulticastLoopback(flag)<span><a class="mark" href="#dgram_socket_setmulticastloopback_flag" id="dgram_socket_setmulticastloopback_flag">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.8</span>
</div><ul>
<li><code>flag</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>Sets or clears the <code>IP_MULTICAST_LOOP</code> socket option. When set to <code>true</code>,
multicast packets will also be received on the local interface.</p>
<h3>socket.setMulticastTTL(ttl)<span><a class="mark" href="#dgram_socket_setmulticastttl_ttl" id="dgram_socket_setmulticastttl_ttl">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.8</span>
</div><ul>
<li><code>ttl</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Integer</li>
</ul>
<p>Sets the <code>IP_MULTICAST_TTL</code> socket option. While TTL generally stands for
"Time to Live", in this context it specifies the number of IP hops that a
packet is allowed to travel through, specifically for multicast traffic. Each
router or gateway that forwards a packet decrements the TTL. If the TTL is
decremented to 0 by a router, it will not be forwarded.</p>
<p>The argument passed to to <code>socket.setMulticastTTL()</code> is a number of hops
between 0 and 255. The default on most systems is <code>1</code> but can vary.</p>
<h3>socket.setTTL(ttl)<span><a class="mark" href="#dgram_socket_setttl_ttl" id="dgram_socket_setttl_ttl">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.101</span>
</div><ul>
<li><code>ttl</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Integer</li>
</ul>
<p>Sets the <code>IP_TTL</code> socket option. While TTL generally stands for "Time to Live",
in this context it specifies the number of IP hops that a packet is allowed to
travel through. Each router or gateway that forwards a packet decrements the
TTL. If the TTL is decremented to 0 by a router, it will not be forwarded.
Changing TTL values is typically done for network probes or when multicasting.</p>
<p>The argument to <code>socket.setTTL()</code> is a number of hops between 1 and 255.
The default on most systems is 64 but can vary.</p>
<h3>socket.ref()<span><a class="mark" href="#dgram_socket_ref" id="dgram_socket_ref">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>By default, binding a socket will cause it to block the Node.js process from
exiting as long as the socket is open. The <code>socket.unref()</code> method can be used
to exclude the socket from the reference counting that keeps the Node.js
process active. The <code>socket.ref()</code> method adds the socket back to the reference
counting and restores the default behavior.</p>
<p>Calling <code>socket.ref()</code> multiples times will have no additional effect.</p>
<p>The <code>socket.ref()</code> method returns a reference to the socket so calls can be
chained.</p>
<h3>socket.unref()<span><a class="mark" href="#dgram_socket_unref" id="dgram_socket_unref">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>By default, binding a socket will cause it to block the Node.js process from
exiting as long as the socket is open. The <code>socket.unref()</code> method can be used
to exclude the socket from the reference counting that keeps the Node.js
process active, allowing the process to exit even if the socket is still
listening.</p>
<p>Calling <code>socket.unref()</code> multiple times will have no addition effect.</p>
<p>The <code>socket.unref()</code> method returns a reference to the socket so calls can be
chained.</p>
<h3>Change to asynchronous <code>socket.bind()</code> behavior<span><a class="mark" href="#dgram_change_to_asynchronous_socket_bind_behavior" id="dgram_change_to_asynchronous_socket_bind_behavior">#</a></span></h3>
<p>As of Node.js v0.10, <a href="#dgram_socket_bind_options_callback"><code>dgram.Socket#bind()</code></a> changed to an asynchronous
execution model. Legacy code that assumes synchronous behavior, as in the
following example:</p>
<pre><code class="lang-js">const s = dgram.createSocket('udp4');
s.bind(1234);
s.addMembership('224.0.0.114');
</code></pre>
<p>Must be changed to pass a callback function to the <a href="#dgram_socket_bind_options_callback"><code>dgram.Socket#bind()</code></a>
function:</p>
<pre><code class="lang-js">const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114');
});
</code></pre>
<h2><code>dgram</code> module functions<span><a class="mark" href="#dgram_dgram_module_functions" id="dgram_dgram_module_functions">#</a></span></h2>
<h3>dgram.createSocket(options[, callback])<span><a class="mark" href="#dgram_dgram_createsocket_options_callback" id="dgram_dgram_createsocket_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.13</span>
</div><ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Attached as a listener to <code>'message'</code> events.</li>
<li>Returns: <a href="dgram.html#dgram_class_dgram_socket" class="type"><dgram.Socket></a></li>
</ul>
<p>Creates a <code>dgram.Socket</code> object. The <code>options</code> argument is an object that
should contain a <code>type</code> field of either <code>udp4</code> or <code>udp6</code> and an optional
boolean <code>reuseAddr</code> field.</p>
<p>When <code>reuseAddr</code> is <code>true</code> <a href="#dgram_socket_bind_port_address_callback"><code>socket.bind()</code></a> will reuse the address, even if
another process has already bound a socket on it. <code>reuseAddr</code> defaults to
<code>false</code>. The optional <code>callback</code> function is added as a listener for <code>'message'</code>
events.</p>
<p>Once the socket is created, calling <a href="#dgram_socket_bind_port_address_callback"><code>socket.bind()</code></a> will instruct the
socket to begin listening for datagram messages. When <code>address</code> and <code>port</code> are
not passed to <a href="#dgram_socket_bind_port_address_callback"><code>socket.bind()</code></a> the method will bind the socket to the "all
interfaces" address on a random port (it does the right thing for both <code>udp4</code>
and <code>udp6</code> sockets). The bound address and port can be retrieved using
<a href="#dgram_socket_address"><code>socket.address().address</code></a> and <a href="#dgram_socket_address"><code>socket.address().port</code></a>.</p>
<h3>dgram.createSocket(type[, callback])<span><a class="mark" href="#dgram_dgram_createsocket_type_callback" id="dgram_dgram_createsocket_type_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><ul>
<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - Either 'udp4' or 'udp6'</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> - Attached as a listener to <code>'message'</code> events.
Optional</li>
<li>Returns: <a href="dgram.html#dgram_class_dgram_socket" class="type"><dgram.Socket></a></li>
</ul>
<p>Creates a <code>dgram.Socket</code> object of the specified <code>type</code>. The <code>type</code> argument
can be either <code>udp4</code> or <code>udp6</code>. An optional <code>callback</code> function can be passed
which is added as a listener for <code>'message'</code> events.</p>
<p>Once the socket is created, calling <a href="#dgram_socket_bind_port_address_callback"><code>socket.bind()</code></a> will instruct the
socket to begin listening for datagram messages. When <code>address</code> and <code>port</code> are
not passed to <a href="#dgram_socket_bind_port_address_callback"><code>socket.bind()</code></a> the method will bind the socket to the "all
interfaces" address on a random port (it does the right thing for both <code>udp4</code>
and <code>udp6</code> sockets). The bound address and port can be retrieved using
<a href="#dgram_socket_address"><code>socket.address().address</code></a> and <a href="#dgram_socket_address"><code>socket.address().port</code></a>.</p>
<!-- [end-include:dgram.md] -->
<!-- [start-include:dns.md] -->
<h1>DNS<span><a class="mark" href="#dns_dns" id="dns_dns">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>The <code>dns</code> module contains functions belonging to two different categories:</p>
<p>1) Functions that use the underlying operating system facilities to perform
name resolution, and that do not necessarily perform any network communication.
This category contains only one function: <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>. <strong>Developers
looking to perform name resolution in the same way that other applications on
the same operating system behave should use <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>.</strong></p>
<p>For example, looking up <code>iana.org</code>.</p>
<pre><code class="lang-js">const dns = require('dns');
dns.lookup('nodejs.org', (err, addresses, family) => {
console.log('addresses:', addresses);
});
// address: "192.0.43.8" family: IPv4
</code></pre>
<p>2) Functions that connect to an actual DNS server to perform name resolution,
and that <em>always</em> use the network to perform DNS queries. This category
contains all functions in the <code>dns</code> module <em>except</em> <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>. These
functions do not use the same set of configuration files used by
<a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a> (e.g. <code>/etc/hosts</code>). These functions should be used by
developers who do not want to use the underlying operating system's facilities
for name resolution, and instead want to <em>always</em> perform DNS queries.</p>
<p>Below is an example that resolves <code>'archive.org'</code> then reverse resolves the IP
addresses that are returned.</p>
<pre><code class="lang-js">const dns = require('dns');
dns.resolve4('archive.org', (err, addresses) => {
if (err) throw err;
console.log(`addresses: ${JSON.stringify(addresses)}`);
addresses.forEach((a) => {
dns.reverse(a, (err, hostnames) => {
if (err) {
throw err;
}
console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`);
});
});
});
</code></pre>
<p>There are subtle consequences in choosing one over the other, please consult
the <a href="#dns_implementation_considerations">Implementation considerations section</a> for more information.</p>
<h2>dns.getServers()<span><a class="mark" href="#dns_dns_getservers" id="dns_dns_getservers">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.3</span>
</div><p>Returns an array of IP address strings that are being used for name
resolution.</p>
<h2>dns.lookup(hostname[, options], callback)<span><a class="mark" href="#dns_dns_lookup_hostname_options_callback" id="dns_dns_lookup_hostname_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Resolves a hostname (e.g. <code>'nodejs.org'</code>) into the first found A (IPv4) or
AAAA (IPv6) record. <code>options</code> can be an object or integer. If <code>options</code> is
not provided, then IPv4 and IPv6 addresses are both valid. If <code>options</code> is
an integer, then it must be <code>4</code> or <code>6</code>.</p>
<p>Alternatively, <code>options</code> can be an object containing these properties:</p>
<ul>
<li><code>family</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> - The record family. If present, must be the integer
<code>4</code> or <code>6</code>. If not provided, both IP v4 and v6 addresses are accepted.</li>
<li><code>hints</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> - If present, it should be one or more of the supported
<code>getaddrinfo</code> flags. If <code>hints</code> is not provided, then no flags are passed to
<code>getaddrinfo</code>. Multiple flags can be passed through <code>hints</code> by bitwise
<code>OR</code>ing their values.
See <a href="#dns_supported_getaddrinfo_flags">supported <code>getaddrinfo</code> flags</a> for more information on supported
flags.</li>
<li><code>all</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> - When <code>true</code>, the callback returns all resolved addresses
in an array, otherwise returns a single address. Defaults to <code>false</code>.</li>
</ul>
<p>All properties are optional. An example usage of options is shown below.</p>
<pre><code>{
family: 4,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
all: false
}
</code></pre><p>The <code>callback</code> function has arguments <code>(err, address, family)</code>. <code>address</code> is a
string representation of an IPv4 or IPv6 address. <code>family</code> is either the
integer <code>4</code> or <code>6</code> and denotes the family of <code>address</code> (not necessarily the
value initially passed to <code>lookup</code>).</p>
<p>With the <code>all</code> option set to <code>true</code>, the arguments change to
<code>(err, addresses)</code>, with <code>addresses</code> being an array of objects with the
properties <code>address</code> and <code>family</code>.</p>
<p>On error, <code>err</code> is an <a href="errors.html#errors_class_error"><code>Error</code></a> object, where <code>err.code</code> is the error code.
Keep in mind that <code>err.code</code> will be set to <code>'ENOENT'</code> not only when
the hostname does not exist but also when the lookup fails in other ways
such as no available file descriptors.</p>
<p><code>dns.lookup()</code> does not necessarily have anything to do with the DNS protocol.
The implementation uses an operating system facility that can associate names
with addresses, and vice versa. This implementation can have subtle but
important consequences on the behavior of any Node.js program. Please take some
time to consult the <a href="#dns_implementation_considerations">Implementation considerations section</a> before using
<code>dns.lookup()</code>.</p>
<p>Example usage:</p>
<pre><code class="lang-js">const dns = require('dns');
const options = {
family: 6,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dns.lookup('example.com', options, (err, address, family) =>
console.log('address: %j family: IPv%s', address, family));
// address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6
// When options.all is true, the result will be an Array.
options.all = true;
dns.lookup('example.com', options, (err, addresses) =>
console.log('addresses: %j', addresses));
// addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}]
</code></pre>
<h3>Supported getaddrinfo flags<span><a class="mark" href="#dns_supported_getaddrinfo_flags" id="dns_supported_getaddrinfo_flags">#</a></span></h3>
<p>The following flags can be passed as hints to <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>.</p>
<ul>
<li><code>dns.ADDRCONFIG</code>: Returned address types are determined by the types
of addresses supported by the current system. For example, IPv4 addresses
are only returned if the current system has at least one IPv4 address
configured. Loopback addresses are not considered.</li>
<li><code>dns.V4MAPPED</code>: If the IPv6 family was specified, but no IPv6 addresses were
found, then return IPv4 mapped IPv6 addresses. Note that it is not supported
on some operating systems (e.g FreeBSD 10.1).</li>
</ul>
<h2>dns.lookupService(address, port, callback)<span><a class="mark" href="#dns_dns_lookupservice_address_port_callback" id="dns_dns_lookupservice_address_port_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>Resolves the given <code>address</code> and <code>port</code> into a hostname and service using
the operating system's underlying <code>getnameinfo</code> implementation.</p>
<p>The callback has arguments <code>(err, hostname, service)</code>. The <code>hostname</code> and
<code>service</code> arguments are strings (e.g. <code>'localhost'</code> and <code>'http'</code> respectively).</p>
<p>On error, <code>err</code> is an <a href="errors.html#errors_class_error"><code>Error</code></a> object, where <code>err.code</code> is the error code.</p>
<pre><code class="lang-js">const dns = require('dns');
dns.lookupService('127.0.0.1', 22, (err, hostname, service) => {
console.log(hostname, service);
// Prints: localhost ssh
});
</code></pre>
<h2>dns.resolve(hostname[, rrtype], callback)<span><a class="mark" href="#dns_dns_resolve_hostname_rrtype_callback" id="dns_dns_resolve_hostname_rrtype_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.27</span>
</div><p>Uses the DNS protocol to resolve a hostname (e.g. <code>'nodejs.org'</code>) into an
array of the record types specified by <code>rrtype</code>.</p>
<p>Valid values for <code>rrtype</code> are:</p>
<ul>
<li><code>'A'</code> - IPV4 addresses, default</li>
<li><code>'AAAA'</code> - IPV6 addresses</li>
<li><code>'MX'</code> - mail exchange records</li>
<li><code>'TXT'</code> - text records</li>
<li><code>'SRV'</code> - SRV records</li>
<li><code>'PTR'</code> - used for reverse IP lookups</li>
<li><code>'NS'</code> - name server records</li>
<li><code>'CNAME'</code> - canonical name records</li>
<li><code>'SOA'</code> - start of authority record</li>
<li><code>'NAPTR'</code> - name authority pointer record</li>
</ul>
<p>The <code>callback</code> function has arguments <code>(err, addresses)</code>. When successful,
<code>addresses</code> will be an array, except when resolving an SOA record which returns
an object structured in the same manner as one returned by the
<a href="#dns_dns_resolvesoa_hostname_callback"><code>dns.resolveSoa()</code></a> method. The type of each item in <code>addresses</code> is
determined by the record type, and described in the documentation for the
corresponding lookup methods.</p>
<p>On error, <code>err</code> is an <a href="errors.html#errors_class_error"><code>Error</code></a> object, where <code>err.code</code> is
one of the error codes listed <a href="#dns_error_codes">here</a>.</p>
<h2>dns.resolve4(hostname, callback)<span><a class="mark" href="#dns_dns_resolve4_hostname_callback" id="dns_dns_resolve4_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><p>Uses the DNS protocol to resolve a IPv4 addresses (<code>A</code> records) for the
<code>hostname</code>. The <code>addresses</code> argument passed to the <code>callback</code> function
will contain an array of IPv4 addresses (e.g.
<code>['74.125.79.104', '74.125.79.105', '74.125.79.106']</code>).</p>
<h2>dns.resolve6(hostname, callback)<span><a class="mark" href="#dns_dns_resolve6_hostname_callback" id="dns_dns_resolve6_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><p>Uses the DNS protocol to resolve a IPv6 addresses (<code>AAAA</code> records) for the
<code>hostname</code>. The <code>addresses</code> argument passed to the <code>callback</code> function
will contain an array of IPv6 addresses.</p>
<h2>dns.resolveCname(hostname, callback)<span><a class="mark" href="#dns_dns_resolvecname_hostname_callback" id="dns_dns_resolvecname_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.2</span>
</div><p>Uses the DNS protocol to resolve <code>CNAME</code> records for the <code>hostname</code>. The
<code>addresses</code> argument passed to the <code>callback</code> function
will contain an array of canonical name records available for the <code>hostname</code>
(e.g. <code>['bar.example.com']</code>).</p>
<h2>dns.resolveMx(hostname, callback)<span><a class="mark" href="#dns_dns_resolvemx_hostname_callback" id="dns_dns_resolvemx_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.27</span>
</div><p>Uses the DNS protocol to resolve mail exchange records (<code>MX</code> records) for the
<code>hostname</code>. The <code>addresses</code> argument passed to the <code>callback</code> function will
contain an array of objects containing both a <code>priority</code> and <code>exchange</code>
property (e.g. <code>[{priority: 10, exchange: 'mx.example.com'}, ...]</code>).</p>
<h2>dns.resolveNaptr(hostname, callback)<span><a class="mark" href="#dns_dns_resolvenaptr_hostname_callback" id="dns_dns_resolvenaptr_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.12</span>
</div><p>Uses the DNS protocol to resolve regular expression based records (<code>NAPTR</code>
records) for the <code>hostname</code>. The <code>callback</code> function has arguments
<code>(err, addresses)</code>. The <code>addresses</code> argument passed to the <code>callback</code> function
will contain an array of objects with the following properties:</p>
<ul>
<li><code>flags</code></li>
<li><code>service</code></li>
<li><code>regexp</code></li>
<li><code>replacement</code></li>
<li><code>order</code></li>
<li><code>preference</code></li>
</ul>
<p>For example:</p>
<pre><code class="lang-js">{
flags: 's',
service: 'SIP+D2U',
regexp: '',
replacement: '_sip._udp.example.com',
order: 30,
preference: 100
}
</code></pre>
<h2>dns.resolveNs(hostname, callback)<span><a class="mark" href="#dns_dns_resolvens_hostname_callback" id="dns_dns_resolvens_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Uses the DNS protocol to resolve name server records (<code>NS</code> records) for the
<code>hostname</code>. The <code>addresses</code> argument passed to the <code>callback</code> function will
contain an array of name server records available for <code>hostname</code>
(e.g. <code>['ns1.example.com', 'ns2.example.com']</code>).</p>
<h2>dns.resolveSoa(hostname, callback)<span><a class="mark" href="#dns_dns_resolvesoa_hostname_callback" id="dns_dns_resolvesoa_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.10</span>
</div><p>Uses the DNS protocol to resolve a start of authority record (<code>SOA</code> record) for
the <code>hostname</code>. The <code>addresses</code> argument passed to the <code>callback</code> function will
be an object with the following properties:</p>
<ul>
<li><code>nsname</code></li>
<li><code>hostmaster</code></li>
<li><code>serial</code></li>
<li><code>refresh</code></li>
<li><code>retry</code></li>
<li><code>expire</code></li>
<li><code>minttl</code></li>
</ul>
<pre><code>{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
</code></pre><h2>dns.resolveSrv(hostname, callback)<span><a class="mark" href="#dns_dns_resolvesrv_hostname_callback" id="dns_dns_resolvesrv_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.27</span>
</div><p>Uses the DNS protocol to resolve service records (<code>SRV</code> records) for the
<code>hostname</code>. The <code>addresses</code> argument passed to the <code>callback</code> function will
be an array of objects with the following properties:</p>
<ul>
<li><code>priority</code></li>
<li><code>weight</code></li>
<li><code>port</code></li>
<li><code>name</code></li>
</ul>
<pre><code>{
priority: 10,
weight: 5,
port: 21223,
name: 'service.example.com'
}
</code></pre><h2>dns.resolveTxt(hostname, callback)<span><a class="mark" href="#dns_dns_resolvetxt_hostname_callback" id="dns_dns_resolvetxt_hostname_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.27</span>
</div><p>Uses the DNS protocol to resolve text queries (<code>TXT</code> records) for the
<code>hostname</code>. The <code>addresses</code> argument passed to the <code>callback</code> function is
is a two-dimentional array of the text records available for <code>hostname</code> (e.g.,
<code>[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]</code>). Each sub-array contains TXT chunks of
one record. Depending on the use case, these could be either joined together or
treated separately.</p>
<h2>dns.reverse(ip, callback)<span><a class="mark" href="#dns_dns_reverse_ip_callback" id="dns_dns_reverse_ip_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><p>Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an
array of hostnames.</p>
<p>The <code>callback</code> function has arguments <code>(err, hostnames)</code>, where <code>hostnames</code>
is an array of resolved hostnames for the given <code>ip</code>.</p>
<p>On error, <code>err</code> is an <a href="errors.html#errors_class_error"><code>Error</code></a> object, where <code>err.code</code> is
one of the <a href="#dns_error_codes">DNS error codes</a>.</p>
<h2>dns.setServers(servers)<span><a class="mark" href="#dns_dns_setservers_servers" id="dns_dns_setservers_servers">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.3</span>
</div><p>Sets the IP addresses of the servers to be used when resolving. The <code>servers</code>
argument is an array of IPv4 or IPv6 addresses.</p>
<p>If a port specified on the address it will be removed.</p>
<p>An error will be thrown if an invalid address is provided.</p>
<p>The <code>dns.setServers()</code> method must not be called while a DNS query is in
progress.</p>
<h2>Error codes<span><a class="mark" href="#dns_error_codes" id="dns_error_codes">#</a></span></h2>
<p>Each DNS query can return one of the following error codes:</p>
<ul>
<li><code>dns.NODATA</code>: DNS server returned answer with no data.</li>
<li><code>dns.FORMERR</code>: DNS server claims query was misformatted.</li>
<li><code>dns.SERVFAIL</code>: DNS server returned general failure.</li>
<li><code>dns.NOTFOUND</code>: Domain name not found.</li>
<li><code>dns.NOTIMP</code>: DNS server does not implement requested operation.</li>
<li><code>dns.REFUSED</code>: DNS server refused query.</li>
<li><code>dns.BADQUERY</code>: Misformatted DNS query.</li>
<li><code>dns.BADNAME</code>: Misformatted hostname.</li>
<li><code>dns.BADFAMILY</code>: Unsupported address family.</li>
<li><code>dns.BADRESP</code>: Misformatted DNS reply.</li>
<li><code>dns.CONNREFUSED</code>: Could not contact DNS servers.</li>
<li><code>dns.TIMEOUT</code>: Timeout while contacting DNS servers.</li>
<li><code>dns.EOF</code>: End of file.</li>
<li><code>dns.FILE</code>: Error reading file.</li>
<li><code>dns.NOMEM</code>: Out of memory.</li>
<li><code>dns.DESTRUCTION</code>: Channel is being destroyed.</li>
<li><code>dns.BADSTR</code>: Misformatted string.</li>
<li><code>dns.BADFLAGS</code>: Illegal flags specified.</li>
<li><code>dns.NONAME</code>: Given hostname is not numeric.</li>
<li><code>dns.BADHINTS</code>: Illegal hints flags specified.</li>
<li><code>dns.NOTINITIALIZED</code>: c-ares library initialization not yet performed.</li>
<li><code>dns.LOADIPHLPAPI</code>: Error loading iphlpapi.dll.</li>
<li><code>dns.ADDRGETNETWORKPARAMS</code>: Could not find GetNetworkParams function.</li>
<li><code>dns.CANCELLED</code>: DNS query cancelled.</li>
</ul>
<h2>Implementation considerations<span><a class="mark" href="#dns_implementation_considerations" id="dns_implementation_considerations">#</a></span></h2>
<p>Although <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a> and the various <code>dns.resolve*()/dns.reverse()</code>
functions have the same goal of associating a network name with a network
address (or vice versa), their behavior is quite different. These differences
can have subtle but significant consequences on the behavior of Node.js
programs.</p>
<h3><code>dns.lookup()</code><span><a class="mark" href="#dns_dns_lookup" id="dns_dns_lookup">#</a></span></h3>
<p>Under the hood, <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a> uses the same operating system facilities
as most other programs. For instance, <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a> will almost always
resolve a given name the same way as the <code>ping</code> command. On most POSIX-like
operating systems, the behavior of the <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a> function can be
modified by changing settings in <a href="http://man7.org/linux/man-pages/man5/nsswitch.conf.5.html">nsswitch.conf(5)</a> and/or <a href="http://man7.org/linux/man-pages/man5/resolv.conf.5.html">resolv.conf(5)</a>,
but note that changing these files will change the behavior of <em>all other
programs running on the same operating system</em>.</p>
<p>Though the call to <code>dns.lookup()</code> will be asynchronous from JavaScript's
perspective, it is implemented as a synchronous call to <a href="http://man7.org/linux/man-pages/man3/getaddrinfo.3.html">getaddrinfo(3)</a> that
runs on libuv's threadpool. Because libuv's threadpool has a fixed size, it
means that if for whatever reason the call to <a href="http://man7.org/linux/man-pages/man3/getaddrinfo.3.html">getaddrinfo(3)</a> takes a long
time, other operations that could run on libuv's threadpool (such as filesystem
operations) will experience degraded performance. In order to mitigate this
issue, one potential solution is to increase the size of libuv's threadpool by
setting the <code>'UV_THREADPOOL_SIZE'</code> environment variable to a value greater than
<code>4</code> (its current default value). For more information on libuv's threadpool, see
<a href="http://docs.libuv.org/en/latest/threadpool.html">the official libuv documentation</a>.</p>
<h3><code>dns.resolve()</code>, <code>dns.resolve*()</code> and <code>dns.reverse()</code><span><a class="mark" href="#dns_dns_resolve_dns_resolve_and_dns_reverse" id="dns_dns_resolve_dns_resolve_and_dns_reverse">#</a></span></h3>
<p>These functions are implemented quite differently than <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>. They
do not use <a href="http://man7.org/linux/man-pages/man3/getaddrinfo.3.html">getaddrinfo(3)</a> and they <em>always</em> perform a DNS query on the
network. This network communication is always done asynchronously, and does not
use libuv's threadpool.</p>
<p>As a result, these functions cannot have the same negative impact on other
processing that happens on libuv's threadpool that <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a> can have.</p>
<p>They do not use the same set of configuration files than what <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>
uses. For instance, <em>they do not use the configuration from <code>/etc/hosts</code></em>.</p>
<!-- [end-include:dns.md] -->
<!-- [start-include:domain.md] -->
<h1>Domain<span><a class="mark" href="#domain_domain" id="domain_domain">#</a></span></h1>
<pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p><strong>This module is pending deprecation</strong>. Once a replacement API has been
finalized, this module will be fully deprecated. Most end users should
<strong>not</strong> have cause to use this module. Users who absolutely must have
the functionality that domains provide may rely on it for the time being
but should expect to have to migrate to a different solution
in the future.</p>
<p>Domains provide a way to handle multiple different IO operations as a
single group. If any of the event emitters or callbacks registered to a
domain emit an <code>'error'</code> event, or throw an error, then the domain object
will be notified, rather than losing the context of the error in the
<code>process.on('uncaughtException')</code> handler, or causing the program to
exit immediately with an error code.</p>
<h2>Warning: Don't Ignore Errors!<span><a class="mark" href="#domain_warning_don_t_ignore_errors" id="domain_warning_don_t_ignore_errors">#</a></span></h2>
<!-- type=misc -->
<p>Domain error handlers are not a substitute for closing down your
process when an error occurs.</p>
<p>By the very nature of how <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/throw"><code>throw</code></a> works in JavaScript, there is almost
never any way to safely "pick up where you left off", without leaking
references, or creating some other sort of undefined brittle state.</p>
<p>The safest way to respond to a thrown error is to shut down the
process. Of course, in a normal web server, you might have many
connections open, and it is not reasonable to abruptly shut those down
because an error was triggered by someone else.</p>
<p>The better approach is to send an error response to the request that
triggered the error, while letting the others finish in their normal
time, and stop listening for new requests in that worker.</p>
<p>In this way, <code>domain</code> usage goes hand-in-hand with the cluster module,
since the master process can fork a new worker when a worker
encounters an error. For Node.js programs that scale to multiple
machines, the terminating proxy or service registry can take note of
the failure, and react accordingly.</p>
<p>For example, this is not a good idea:</p>
<pre><code class="lang-js">// XXX WARNING! BAD IDEA!
const d = require('domain').create();
d.on('error', (er) => {
// The error won't crash the process, but what it does is worse!
// Though we've prevented abrupt process restarting, we are leaking
// resources like crazy if this ever happens.
// This is no better than process.on('uncaughtException')!
console.log(`error, but oh well ${er.message}`);
});
d.run(() => {
require('http').createServer((req, res) => {
handleRequest(req, res);
}).listen(PORT);
});
</code></pre>
<p>By using the context of a domain, and the resilience of separating our
program into multiple worker processes, we can react more
appropriately, and handle errors with much greater safety.</p>
<pre><code class="lang-js">// Much better!
const cluster = require('cluster');
const PORT = +process.env.PORT || 1337;
if (cluster.isMaster) {
// In real life, you'd probably use more than just 2 workers,
// and perhaps not put the master and worker in the same file.
//
// You can also of course get a bit fancier about logging, and
// implement whatever custom logic you need to prevent DoS
// attacks and other bad behavior.
//
// See the options in the cluster documentation.
//
// The important thing is that the master does very little,
// increasing our resilience to unexpected errors.
cluster.fork();
cluster.fork();
cluster.on('disconnect', (worker) => {
console.error('disconnect!');
cluster.fork();
});
} else {
// the worker
//
// This is where we put our bugs!
const domain = require('domain');
// See the cluster documentation for more details about using
// worker processes to serve requests. How it works, caveats, etc.
const server = require('http').createServer((req, res) => {
const d = domain.create();
d.on('error', (er) => {
console.error(`error ${er.stack}`);
// Note: we're in dangerous territory!
// By definition, something unexpected occurred,
// which we probably didn't want.
// Anything can happen now! Be very careful!
try {
// make sure we close down within 30 seconds
const killtimer = setTimeout(() => {
process.exit(1);
}, 30000);
// But don't keep the process open just for that!
killtimer.unref();
// stop taking new requests.
server.close();
// Let the master know we're dead. This will trigger a
// 'disconnect' in the cluster master, and then it will fork
// a new worker.
cluster.worker.disconnect();
// try to send an error to the request that triggered the problem
res.statusCode = 500;
res.setHeader('content-type', 'text/plain');
res.end('Oops, there was a problem!\n');
} catch (er2) {
// oh well, not much we can do at this point.
console.error(`Error sending 500! ${er2.stack}`);
}
});
// Because req and res were created before this domain existed,
// we need to explicitly add them.
// See the explanation of implicit vs explicit binding below.
d.add(req);
d.add(res);
// Now run the handler function in the domain.
d.run(() => {
handleRequest(req, res);
});
});
server.listen(PORT);
}
// This part isn't important. Just an example routing thing.
// You'd put your fancy application logic here.
function handleRequest(req, res) {
switch (req.url) {
case '/error':
// We do some async stuff, and then...
setTimeout(() => {
// Whoops!
flerb.bark();
});
break;
default:
res.end('ok');
}
}
</code></pre>
<h2>Additions to Error objects<span><a class="mark" href="#domain_additions_to_error_objects" id="domain_additions_to_error_objects">#</a></span></h2>
<!-- type=misc -->
<p>Any time an <code>Error</code> object is routed through a domain, a few extra fields
are added to it.</p>
<ul>
<li><code>error.domain</code> The domain that first handled the error.</li>
<li><code>error.domainEmitter</code> The event emitter that emitted an <code>'error'</code> event
with the error object.</li>
<li><code>error.domainBound</code> The callback function which was bound to the
domain, and passed an error as its first argument.</li>
<li><code>error.domainThrown</code> A boolean indicating whether the error was
thrown, emitted, or passed to a bound callback function.</li>
</ul>
<h2>Implicit Binding<span><a class="mark" href="#domain_implicit_binding" id="domain_implicit_binding">#</a></span></h2>
<!--type=misc-->
<p>If domains are in use, then all <strong>new</strong> EventEmitter objects (including
Stream objects, requests, responses, etc.) will be implicitly bound to
the active domain at the time of their creation.</p>
<p>Additionally, callbacks passed to lowlevel event loop requests (such as
to fs.open, or other callback-taking methods) will automatically be
bound to the active domain. If they throw, then the domain will catch
the error.</p>
<p>In order to prevent excessive memory usage, Domain objects themselves
are not implicitly added as children of the active domain. If they
were, then it would be too easy to prevent request and response objects
from being properly garbage collected.</p>
<p>If you <em>want</em> to nest Domain objects as children of a parent Domain,
then you must explicitly add them.</p>
<p>Implicit binding routes thrown errors and <code>'error'</code> events to the
Domain's <code>'error'</code> event, but does not register the EventEmitter on the
Domain, so <a href="#domain_domain_dispose"><code>domain.dispose()</code></a> will not shut down the EventEmitter.
Implicit binding only takes care of thrown errors and <code>'error'</code> events.</p>
<h2>Explicit Binding<span><a class="mark" href="#domain_explicit_binding" id="domain_explicit_binding">#</a></span></h2>
<!--type=misc-->
<p>Sometimes, the domain in use is not the one that ought to be used for a
specific event emitter. Or, the event emitter could have been created
in the context of one domain, but ought to instead be bound to some
other domain.</p>
<p>For example, there could be one domain in use for an HTTP server, but
perhaps we would like to have a separate domain to use for each request.</p>
<p>That is possible via explicit binding.</p>
<p>For example:</p>
<pre><code class="lang-js">// create a top-level domain for the server
const domain = require('domain');
const http = require('http');
const serverDomain = domain.create();
serverDomain.run(() => {
// server is created in the scope of serverDomain
http.createServer((req, res) => {
// req and res are also created in the scope of serverDomain
// however, we'd prefer to have a separate domain for each request.
// create it first thing, and add req and res to it.
const reqd = domain.create();
reqd.add(req);
reqd.add(res);
reqd.on('error', (er) => {
console.error('Error', er, req.url);
try {
res.writeHead(500);
res.end('Error occurred, sorry.');
} catch (er2) {
console.error('Error sending 500', er2, req.url);
}
});
}).listen(1337);
});
</code></pre>
<h2>domain.create()<span><a class="mark" href="#domain_domain_create" id="domain_domain_create">#</a></span></h2>
<div class="signature"><ul>
<li>Returns: <span class="type"><Domain></span></li>
</ul>
</div><p>Returns a new Domain object.</p>
<h2>Class: Domain<span><a class="mark" href="#domain_class_domain" id="domain_class_domain">#</a></span></h2>
<p>The Domain class encapsulates the functionality of routing errors and
uncaught exceptions to the active Domain object.</p>
<p>Domain is a child class of <a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a>. To handle the errors that it
catches, listen to its <code>'error'</code> event.</p>
<h3>domain.run(fn[, arg][, ...])<span><a class="mark" href="#domain_domain_run_fn_arg" id="domain_domain_run_fn_arg">#</a></span></h3>
<div class="signature"><ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
</div><p>Run the supplied function in the context of the domain, implicitly
binding all event emitters, timers, and lowlevel requests that are
created in that context. Optionally, arguments can be passed to
the function.</p>
<p>This is the most basic way to use a domain.</p>
<p>Example:</p>
<pre><code class="lang-js">const domain = require('domain');
const fs = require('fs');
const d = domain.create();
d.on('error', (er) => {
console.error('Caught error!', er);
});
d.run(() => {
process.nextTick(() => {
setTimeout(() => { // simulating some various async stuff
fs.open('non-existent file', 'r', (er, fd) => {
if (er) throw er;
// proceed...
});
}, 100);
});
});
</code></pre>
<p>In this example, the <code>d.on('error')</code> handler will be triggered, rather
than crashing the program.</p>
<h3>domain.members<span><a class="mark" href="#domain_domain_members" id="domain_domain_members">#</a></span></h3>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a></li>
</ul>
</div><p>An array of timers and event emitters that have been explicitly added
to the domain.</p>
<h3>domain.add(emitter)<span><a class="mark" href="#domain_domain_add_emitter" id="domain_domain_add_emitter">#</a></span></h3>
<div class="signature"><ul>
<li><code>emitter</code> <a href="events.html#events_class_events_eventemitter" class="type"><EventEmitter></a> | <a href="timers.html#timers_timers" class="type"><Timer></a> emitter or timer to be added to the domain</li>
</ul>
</div><p>Explicitly adds an emitter to the domain. If any event handlers called by
the emitter throw an error, or if the emitter emits an <code>'error'</code> event, it
will be routed to the domain's <code>'error'</code> event, just like with implicit
binding.</p>
<p>This also works with timers that are returned from <a href="timers.html#timers_setinterval_callback_delay_arg"><code>setInterval()</code></a> and
<a href="timers.html#timers_settimeout_callback_delay_arg"><code>setTimeout()</code></a>. If their callback function throws, it will be caught by
the domain 'error' handler.</p>
<p>If the Timer or EventEmitter was already bound to a domain, it is removed
from that one, and bound to this one instead.</p>
<h3>domain.remove(emitter)<span><a class="mark" href="#domain_domain_remove_emitter" id="domain_domain_remove_emitter">#</a></span></h3>
<div class="signature"><ul>
<li><code>emitter</code> <a href="events.html#events_class_events_eventemitter" class="type"><EventEmitter></a> | <a href="timers.html#timers_timers" class="type"><Timer></a> emitter or timer to be removed from the domain</li>
</ul>
</div><p>The opposite of <a href="#domain_domain_add_emitter"><code>domain.add(emitter)</code></a>. Removes domain handling from the
specified emitter.</p>
<h3>domain.bind(callback)<span><a class="mark" href="#domain_domain_bind_callback" id="domain_domain_bind_callback">#</a></span></h3>
<div class="signature"><ul>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The callback function</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The bound function</li>
</ul>
</div><p>The returned function will be a wrapper around the supplied callback
function. When the returned function is called, any errors that are
thrown will be routed to the domain's <code>'error'</code> event.</p>
<h4>Example<span><a class="mark" href="#domain_example" id="domain_example">#</a></span></h4>
<pre><code class="lang-js">const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.bind((er, data) => {
// if this throws, it will also be passed to the domain
return cb(er, data ? JSON.parse(data) : null);
}));
}
d.on('error', (er) => {
// an error occurred somewhere.
// if we throw it now, it will crash the program
// with the normal line number and stack message.
});
</code></pre>
<h3>domain.intercept(callback)<span><a class="mark" href="#domain_domain_intercept_callback" id="domain_domain_intercept_callback">#</a></span></h3>
<div class="signature"><ul>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The callback function</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The intercepted function</li>
</ul>
</div><p>This method is almost identical to <a href="#domain_domain_bind_callback"><code>domain.bind(callback)</code></a>. However, in
addition to catching thrown errors, it will also intercept <a href="errors.html#errors_class_error"><code>Error</code></a>
objects sent as the first argument to the function.</p>
<p>In this way, the common <code>if (err) return callback(err);</code> pattern can be replaced
with a single error handler in a single place.</p>
<h4>Example<span><a class="mark" href="#domain_example_1" id="domain_example_1">#</a></span></h4>
<pre><code class="lang-js">const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.intercept((data) => {
// note, the first argument is never passed to the
// callback since it is assumed to be the 'Error' argument
// and thus intercepted by the domain.
// if this throws, it will also be passed to the domain
// so the error-handling logic can be moved to the 'error'
// event on the domain instead of being repeated throughout
// the program.
return cb(null, JSON.parse(data));
}));
}
d.on('error', (er) => {
// an error occurred somewhere.
// if we throw it now, it will crash the program
// with the normal line number and stack message.
});
</code></pre>
<h3>domain.enter()<span><a class="mark" href="#domain_domain_enter" id="domain_domain_enter">#</a></span></h3>
<p>The <code>enter</code> method is plumbing used by the <code>run</code>, <code>bind</code>, and <code>intercept</code>
methods to set the active domain. It sets <code>domain.active</code> and <code>process.domain</code>
to the domain, and implicitly pushes the domain onto the domain stack managed
by the domain module (see <a href="#domain_domain_exit"><code>domain.exit()</code></a> for details on the domain stack). The
call to <code>enter</code> delimits the beginning of a chain of asynchronous calls and I/O
operations bound to a domain.</p>
<p>Calling <code>enter</code> changes only the active domain, and does not alter the domain
itself. <code>enter</code> and <code>exit</code> can be called an arbitrary number of times on a
single domain.</p>
<p>If the domain on which <code>enter</code> is called has been disposed, <code>enter</code> will return
without setting the domain.</p>
<h3>domain.exit()<span><a class="mark" href="#domain_domain_exit" id="domain_domain_exit">#</a></span></h3>
<p>The <code>exit</code> method exits the current domain, popping it off the domain stack.
Any time execution is going to switch to the context of a different chain of
asynchronous calls, it's important to ensure that the current domain is exited.
The call to <code>exit</code> delimits either the end of or an interruption to the chain
of asynchronous calls and I/O operations bound to a domain.</p>
<p>If there are multiple, nested domains bound to the current execution context,
<code>exit</code> will exit any domains nested within this domain.</p>
<p>Calling <code>exit</code> changes only the active domain, and does not alter the domain
itself. <code>enter</code> and <code>exit</code> can be called an arbitrary number of times on a
single domain.</p>
<p>If the domain on which <code>exit</code> is called has been disposed, <code>exit</code> will return
without exiting the domain.</p>
<h3>domain.dispose()<span><a class="mark" href="#domain_domain_dispose" id="domain_domain_dispose">#</a></span></h3>
<pre class="api_stability api_stability_0">Stability: 0 - Deprecated. Please recover from failed IO actions explicitly via error event handlers set on the domain.</pre><p>Once <code>dispose</code> has been called, the domain will no longer be used by callbacks
bound into the domain via <code>run</code>, <code>bind</code>, or <code>intercept</code>, and a <code>'dispose'</code> event
is emitted.</p>
<!-- [end-include:domain.md] -->
<!-- [start-include:errors.md] -->
<h1>Errors<span><a class="mark" href="#errors_errors" id="errors_errors">#</a></span></h1>
<!--type=misc-->
<p>Applications running in Node.js will generally experience four categories of
errors:</p>
<ul>
<li>Standard JavaScript errors such as:<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/EvalError" class="type"><EvalError></a> : thrown when a call to <code>eval()</code> fails.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SyntaxError" class="type"><SyntaxError></a> : thrown in response to improper JavaScript language
syntax.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RangeError" class="type"><RangeError></a> : thrown when a value is not within an expected range</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ReferenceError" class="type"><ReferenceError></a> : thrown when using undefined variables</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError" class="type"><TypeError></a> : thrown when passing arguments of the wrong type</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/URIError" class="type"><URIError></a> : thrown when a global URI handling function is misused.</li>
</ul>
</li>
<li>System errors triggered by underlying operating system constraints such
as attempting to open a file that does not exist, attempting to send data
over a closed socket, etc;</li>
<li>And User-specified errors triggered by application code.</li>
<li>Assertion Errors are a special class of error that can be triggered whenever
Node.js detects an exceptional logic violation that should never occur. These
are raised typically by the <code>assert</code> module.</li>
</ul>
<p>All JavaScript and System errors raised by Node.js inherit from, or are
instances of, the standard JavaScript <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a> class and are guaranteed
to provide <em>at least</em> the properties available on that class.</p>
<h2>Error Propagation and Interception<span><a class="mark" href="#errors_error_propagation_and_interception" id="errors_error_propagation_and_interception">#</a></span></h2>
<!--type=misc-->
<p>Node.js supports several mechanisms for propagating and handling errors that
occur while an application is running. How these errors are reported and
handled depends entirely on the type of Error and the style of the API that is
called.</p>
<p>All JavaScript errors are handled as exceptions that <em>immediately</em> generate
and throw an error using the standard JavaScript <code>throw</code> mechanism. These
are handled using the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch"><code>try / catch</code> construct</a> provided by the JavaScript
language.</p>
<pre><code class="lang-js">// Throws with a ReferenceError because z is undefined
try {
const m = 1;
const n = m + z;
} catch (err) {
// Handle the error here.
}
</code></pre>
<p>Any use of the JavaScript <code>throw</code> mechanism will raise an exception that
<em>must</em> be handled using <code>try / catch</code> or the Node.js process will exit
immediately.</p>
<p>With few exceptions, <em>Synchronous</em> APIs (any blocking method that does not
accept a <code>callback</code> function, such as <a href="fs.html#fs_fs_readfilesync_file_options"><code>fs.readFileSync</code></a>), will use <code>throw</code>
to report errors.</p>
<p>Errors that occur within <em>Asynchronous APIs</em> may be reported in multiple ways:</p>
<ul>
<li><p>Most asynchronous methods that accept a <code>callback</code> function will accept an
<code>Error</code> object passed as the first argument to that function. If that first
argument is not <code>null</code> and is an instance of <code>Error</code>, then an error occurred
that should be handled.</p>
<pre><code class="lang-js">const fs = require('fs');
fs.readFile('a file that does not exist', (err, data) => {
if (err) {
console.error('There was an error reading the file!', err);
return;
}
// Otherwise handle the data
});
</code></pre>
</li>
<li><p>When an asynchronous method is called on an object that is an <code>EventEmitter</code>,
errors can be routed to that object's <code>'error'</code> event.</p>
<pre><code class="lang-js">const net = require('net');
const connection = net.connect('localhost');
// Adding an 'error' event handler to a stream:
connection.on('error', (err) => {
// If the connection is reset by the server, or if it can't
// connect at all, or on any sort of error encountered by
// the connection, the error will be sent here.
console.error(err);
});
connection.pipe(process.stdout);
</code></pre>
</li>
<li><p>A handful of typically asynchronous methods in the Node.js API may still
use the <code>throw</code> mechanism to raise exceptions that must be handled using
<code>try / catch</code>. There is no comprehensive list of such methods; please
refer to the documentation of each method to determine the appropriate
error handling mechanism required.</p>
</li>
</ul>
<p>The use of the <code>'error'</code> event mechanism is most common for <a href="stream.html">stream-based</a>
and <a href="events.html#events_class_events_eventemitter">event emitter-based</a> APIs, which themselves represent a series of
asynchronous operations over time (as opposed to a single operation that may
pass or fail).</p>
<p>For <em>all</em> <code>EventEmitter</code> objects, if an <code>'error'</code> event handler is not
provided, the error will be thrown, causing the Node.js process to report an
unhandled exception and crash unless either: The <a href="domain.html"><code>domain</code></a> module is used
appropriately or a handler has been registered for the
<a href="process.html#process_event_uncaughtexception"><code>process.on('uncaughtException')</code></a> event.</p>
<pre><code class="lang-js">const EventEmitter = require('events');
const ee = new EventEmitter();
setImmediate(() => {
// This will crash the process because no 'error' event
// handler has been added.
ee.emit('error', new Error('This will crash'));
});
</code></pre>
<p>Errors generated in this way <em>cannot</em> be intercepted using <code>try / catch</code> as
they are thrown <em>after</em> the calling code has already exited.</p>
<p>Developers must refer to the documentation for each method to determine
exactly how errors raised by those methods are propagated.</p>
<h3>Node.js style callbacks<span><a class="mark" href="#errors_node_js_style_callbacks" id="errors_node_js_style_callbacks">#</a></span></h3>
<!--type=misc-->
<p>Most asynchronous methods exposed by the Node.js core API follow an idiomatic
pattern referred to as a "Node.js style callback". With this pattern, a
callback function is passed to the method as an argument. When the operation
either completes or an error is raised, the callback function is called with
the Error object (if any) passed as the first argument. If no error was raised,
the first argument will be passed as <code>null</code>.</p>
<pre><code class="lang-js">const fs = require('fs');
function nodeStyleCallback(err, data) {
if (err) {
console.error('There was an error', err);
return;
}
console.log(data);
}
fs.readFile('/some/file/that/does-not-exist', nodeStyleCallback);
fs.readFile('/some/file/that/does-exist', nodeStyleCallback)
</code></pre>
<p>The JavaScript <code>try / catch</code> mechanism <strong>cannot</strong> be used to intercept errors
generated by asynchronous APIs. A common mistake for beginners is to try to
use <code>throw</code> inside a Node.js style callback:</p>
<pre><code class="lang-js">// THIS WILL NOT WORK:
const fs = require('fs');
try {
fs.readFile('/some/file/that/does-not-exist', (err, data) => {
// mistaken assumption: throwing here...
if (err) {
throw err;
}
});
} catch(err) {
// This will not catch the throw!
console.log(err);
}
</code></pre>
<p>This will not work because the callback function passed to <code>fs.readFile()</code> is
called asynchronously. By the time the callback has been called, the
surrounding code (including the <code>try { } catch(err) { }</code> block will have
already exited. Throwing an error inside the callback <strong>can crash the Node.js
process</strong> in most cases. If <a href="domain.html">domains</a> are enabled, or a handler has been
registered with <code>process.on('uncaughtException')</code>, such errors can be
intercepted.</p>
<h2>Class: Error<span><a class="mark" href="#errors_class_error" id="errors_class_error">#</a></span></h2>
<!--type=class-->
<p>A generic JavaScript <code>Error</code> object that does not denote any specific
circumstance of why the error occurred. <code>Error</code> objects capture a "stack trace"
detailing the point in the code at which the <code>Error</code> was instantiated, and may
provide a text description of the error.</p>
<p>All errors generated by Node.js, including all System and JavaScript errors,
will either be instances of, or inherit from, the <code>Error</code> class.</p>
<h3>new Error(message)<span><a class="mark" href="#errors_new_error_message" id="errors_new_error_message">#</a></span></h3>
<div class="signature"><ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
</div><p>Creates a new <code>Error</code> object and sets the <code>error.message</code> property to the
provided text message. If an object is passed as <code>message</code>, the text message
is generated by calling <code>message.toString()</code>. The <code>error.stack</code> property will
represent the point in the code at which <code>new Error()</code> was called. Stack traces
are dependent on <a href="https://github.com/v8/v8/wiki/Stack-Trace-API">V8's stack trace API</a>. Stack traces extend only to either
(a) the beginning of <em>synchronous code execution</em>, or (b) the number of frames
given by the property <code>Error.stackTraceLimit</code>, whichever is smaller.</p>
<h3>Error.captureStackTrace(targetObject[, constructorOpt])<span><a class="mark" href="#errors_error_capturestacktrace_targetobject_constructoropt" id="errors_error_capturestacktrace_targetobject_constructoropt">#</a></span></h3>
<div class="signature"><ul>
<li><code>targetObject</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>constructorOpt</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
</div><p>Creates a <code>.stack</code> property on <code>targetObject</code>, which when accessed returns
a string representing the location in the code at which
<code>Error.captureStackTrace()</code> was called.</p>
<pre><code class="lang-js">const myObject = {};
Error.captureStackTrace(myObject);
myObject.stack // similar to `new Error().stack`
</code></pre>
<p>The first line of the trace, instead of being prefixed with <code>ErrorType:
message</code>, will be the result of calling <code>targetObject.toString()</code>.</p>
<p>The optional <code>constructorOpt</code> argument accepts a function. If given, all frames
above <code>constructorOpt</code>, including <code>constructorOpt</code>, will be omitted from the
generated stack trace.</p>
<p>The <code>constructorOpt</code> argument is useful for hiding implementation
details of error generation from an end user. For instance:</p>
<pre><code class="lang-js">function MyError() {
Error.captureStackTrace(this, MyError);
}
// Without passing MyError to captureStackTrace, the MyError
// frame would show up in the .stack property. By passing
// the constructor, we omit that frame and all frames above it.
new MyError().stack
</code></pre>
<h3>Error.stackTraceLimit<span><a class="mark" href="#errors_error_stacktracelimit" id="errors_error_stacktracelimit">#</a></span></h3>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>The <code>Error.stackTraceLimit</code> property specifies the number of stack frames
collected by a stack trace (whether generated by <code>new Error().stack</code> or
<code>Error.captureStackTrace(obj)</code>).</p>
<p>The default value is <code>10</code> but may be set to any valid JavaScript number. Changes
will affect any stack trace captured <em>after</em> the value has been changed.</p>
<p>If set to a non-number value, or set to a negative number, stack traces will
not capture any frames.</p>
<h4>error.message<span><a class="mark" href="#errors_error_message" id="errors_error_message">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
</div><p>The <code>error.message</code> property is the string description of the error as set by calling <code>new Error(message)</code>.
The <code>message</code> passed to the constructor will also appear in the first line of
the stack trace of the <code>Error</code>, however changing this property after the
<code>Error</code> object is created <em>may not</em> change the first line of the stack trace
(for example, when <code>error.stack</code> is read before this property is changed).</p>
<pre><code class="lang-js">const err = new Error('The message');
console.log(err.message);
// Prints: The message
</code></pre>
<h4>error.stack<span><a class="mark" href="#errors_error_stack" id="errors_error_stack">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
</div><p>The <code>error.stack</code> property is a string describing the point in the code at which
the <code>Error</code> was instantiated.</p>
<p>For example:</p>
<pre><code>Error: Things keep happening!
at /home/gbusey/file.js:525:2
at Frobnicator.refrobulate (/home/gbusey/business-logic.js:424:21)
at Actor.<anonymous> (/home/gbusey/actors.js:400:8)
at increaseSynergy (/home/gbusey/actors.js:701:6)
</code></pre><p>The first line is formatted as <code><error class name>: <error message></code>, and
is followed by a series of stack frames (each line beginning with "at ").
Each frame describes a call site within the code that lead to the error being
generated. V8 attempts to display a name for each function (by variable name,
function name, or object method name), but occasionally it will not be able to
find a suitable name. If V8 cannot determine a name for the function, only
location information will be displayed for that frame. Otherwise, the
determined function name will be displayed with location information appended
in parentheses.</p>
<p>It is important to note that frames are <strong>only</strong> generated for JavaScript
functions. If, for example, execution synchronously passes through a C++ addon
function called <code>cheetahify</code>, which itself calls a JavaScript function, the
frame representing the <code>cheetahify</code> call will <strong>not</strong> be present in the stack
traces:</p>
<pre><code class="lang-js">const cheetahify = require('./native-binding.node');
function makeFaster() {
// cheetahify *synchronously* calls speedy.
cheetahify(function speedy() {
throw new Error('oh no!');
});
}
makeFaster(); // will throw:
// /home/gbusey/file.js:6
// throw new Error('oh no!');
// ^
// Error: oh no!
// at speedy (/home/gbusey/file.js:6:11)
// at makeFaster (/home/gbusey/file.js:5:3)
// at Object.<anonymous> (/home/gbusey/file.js:10:1)
// at Module._compile (module.js:456:26)
// at Object.Module._extensions..js (module.js:474:10)
// at Module.load (module.js:356:32)
// at Function.Module._load (module.js:312:12)
// at Function.Module.runMain (module.js:497:10)
// at startup (node.js:119:16)
// at node.js:906:3
</code></pre>
<p>The location information will be one of:</p>
<ul>
<li><code>native</code>, if the frame represents a call internal to V8 (as in <code>[].forEach</code>).</li>
<li><code>plain-filename.js:line:column</code>, if the frame represents a call internal
to Node.js.</li>
<li><code>/absolute/path/to/file.js:line:column</code>, if the frame represents a call in
a user program, or its dependencies.</li>
</ul>
<p>The string representing the stack trace is lazily generated when the
<code>error.stack</code> property is <strong>accessed</strong>.</p>
<p>The number of frames captured by the stack trace is bounded by the smaller of
<code>Error.stackTraceLimit</code> or the number of available frames on the current event
loop tick.</p>
<p>System-level errors are generated as augmented <code>Error</code> instances, which are
detailed <a href="#errors_system_errors">here</a>.</p>
<h2>Class: RangeError<span><a class="mark" href="#errors_class_rangeerror" id="errors_class_rangeerror">#</a></span></h2>
<p>A subclass of <code>Error</code> that indicates that a provided argument was not within the
set or range of acceptable values for a function; whether that is a numeric
range, or outside the set of options for a given function parameter.</p>
<p>For example:</p>
<pre><code class="lang-js">require('net').connect(-1);
// throws RangeError, port should be > 0 && < 65536
</code></pre>
<p>Node.js will generate and throw <code>RangeError</code> instances <em>immediately</em> as a form
of argument validation.</p>
<h2>Class: ReferenceError<span><a class="mark" href="#errors_class_referenceerror" id="errors_class_referenceerror">#</a></span></h2>
<p>A subclass of <code>Error</code> that indicates that an attempt is being made to access a
variable that is not defined. Such errors commonly indicate typos in code, or
an otherwise broken program.</p>
<p>While client code may generate and propagate these errors, in practice, only V8
will do so.</p>
<pre><code class="lang-js">doesNotExist;
// throws ReferenceError, doesNotExist is not a variable in this program.
</code></pre>
<p><code>ReferenceError</code> instances will have an <code>error.arguments</code> property whose value
is an array containing a single element: a string representing the variable
that was not defined.</p>
<pre><code class="lang-js">const assert = require('assert');
try {
doesNotExist;
} catch(err) {
assert(err.arguments[0], 'doesNotExist');
}
</code></pre>
<p>Unless an application is dynamically generating and running code,
<code>ReferenceError</code> instances should always be considered a bug in the code
or its dependencies.</p>
<h2>Class: SyntaxError<span><a class="mark" href="#errors_class_syntaxerror" id="errors_class_syntaxerror">#</a></span></h2>
<p>A subclass of <code>Error</code> that indicates that a program is not valid JavaScript.
These errors may only be generated and propagated as a result of code
evaluation. Code evaluation may happen as a result of <code>eval</code>, <code>Function</code>,
<code>require</code>, or <a href="vm.html">vm</a>. These errors are almost always indicative of a broken
program.</p>
<pre><code class="lang-js">try {
require('vm').runInThisContext('binary ! isNotOk');
} catch(err) {
// err will be a SyntaxError
}
</code></pre>
<p><code>SyntaxError</code> instances are unrecoverable in the context that created them –
they may only be caught by other contexts.</p>
<h2>Class: TypeError<span><a class="mark" href="#errors_class_typeerror" id="errors_class_typeerror">#</a></span></h2>
<p>A subclass of <code>Error</code> that indicates that a provided argument is not an
allowable type. For example, passing a function to a parameter which expects a
string would be considered a TypeError.</p>
<pre><code class="lang-js">require('url').parse(() => { });
// throws TypeError, since it expected a string
</code></pre>
<p>Node.js will generate and throw <code>TypeError</code> instances <em>immediately</em> as a form
of argument validation.</p>
<h2>Exceptions vs. Errors<span><a class="mark" href="#errors_exceptions_vs_errors" id="errors_exceptions_vs_errors">#</a></span></h2>
<!--type=misc-->
<p>A JavaScript exception is a value that is thrown as a result of an invalid
operation or as the target of a <code>throw</code> statement. While it is not required
that these values are instances of <code>Error</code> or classes which inherit from
<code>Error</code>, all exceptions thrown by Node.js or the JavaScript runtime <em>will</em> be
instances of Error.</p>
<p>Some exceptions are <em>unrecoverable</em> at the JavaScript layer. Such exceptions
will <em>always</em> cause the Node.js process to crash. Examples include <code>assert()</code>
checks or <code>abort()</code> calls in the C++ layer.</p>
<h2>System Errors<span><a class="mark" href="#errors_system_errors" id="errors_system_errors">#</a></span></h2>
<p>System errors are generated when exceptions occur within the program's
runtime environment. Typically, these are operational errors that occur
when an application violates an operating system constraint such as attempting
to read a file that does not exist or when the user does not have sufficient
permissions.</p>
<p>System errors are typically generated at the syscall level: an exhaustive list
of error codes and their meanings is available by running <code>man 2 intro</code> or
<code>man 3 errno</code> on most Unices; or <a href="http://man7.org/linux/man-pages/man3/errno.3.html">online</a>.</p>
<p>In Node.js, system errors are represented as augmented <code>Error</code> objects with
added properties.</p>
<h3>Class: System Error<span><a class="mark" href="#errors_class_system_error" id="errors_class_system_error">#</a></span></h3>
<h4>error.code<span><a class="mark" href="#errors_error_code" id="errors_error_code">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
</div><p>The <code>error.code</code> property is a string representing the error code, which is always
<code>E</code> followed by a sequence of capital letters.</p>
<h4>error.errno<span><a class="mark" href="#errors_error_errno" id="errors_error_errno">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>The <code>error.errno</code> property is a number or a string.
The number is a <strong>negative</strong> value which corresponds to the error code defined in
<a href="http://docs.libuv.org/en/v1.x/errors.html"><code>libuv Error handling</code></a>. See uv-errno.h header file (<code>deps/uv/include/uv-errno.h</code> in
the Node.js source tree) for details.
In case of a string, it is the same as <code>error.code</code>.</p>
<h4>error.syscall<span><a class="mark" href="#errors_error_syscall" id="errors_error_syscall">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
</div><p>The <code>error.syscall</code> property is a string describing the <a href="http://man7.org/linux/man-pages/man2/syscall.2.html">syscall</a> that failed.</p>
<h4>error.path<span><a class="mark" href="#errors_error_path" id="errors_error_path">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
</div><p>When present (e.g. in <code>fs</code> or <code>child_process</code>), the <code>error.path</code> property is a string
containing a relevant invalid pathname.</p>
<h4>error.address<span><a class="mark" href="#errors_error_address" id="errors_error_address">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
</div><p>When present (e.g. in <code>net</code> or <code>dgram</code>), the <code>error.address</code> property is a string
describing the address to which the connection failed.</p>
<h4>error.port<span><a class="mark" href="#errors_error_port" id="errors_error_port">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
</ul>
</div><p>When present (e.g. in <code>net</code> or <code>dgram</code>), the <code>error.port</code> property is a number representing
the connection's port that is not available.</p>
<h3>Common System Errors<span><a class="mark" href="#errors_common_system_errors" id="errors_common_system_errors">#</a></span></h3>
<p>This list is <strong>not exhaustive</strong>, but enumerates many of the common system
errors encountered when writing a Node.js program. An exhaustive list may be
found <a href="http://man7.org/linux/man-pages/man3/errno.3.html">here</a>.</p>
<ul>
<li><p><code>EACCES</code> (Permission denied): An attempt was made to access a file in a way
forbidden by its file access permissions.</p>
</li>
<li><p><code>EADDRINUSE</code> (Address already in use): An attempt to bind a server
(<a href="net.html"><code>net</code></a>, <a href="http.html"><code>http</code></a>, or <a href="https.html"><code>https</code></a>) to a local address failed due to
another server on the local system already occupying that address.</p>
</li>
<li><p><code>ECONNREFUSED</code> (Connection refused): No connection could be made because the
target machine actively refused it. This usually results from trying to
connect to a service that is inactive on the foreign host.</p>
</li>
<li><p><code>ECONNRESET</code> (Connection reset by peer): A connection was forcibly closed by
a peer. This normally results from a loss of the connection on the remote
socket due to a timeout or reboot. Commonly encountered via the <a href="http.html"><code>http</code></a>
and <a href="net.html"><code>net</code></a> modules.</p>
</li>
<li><p><code>EEXIST</code> (File exists): An existing file was the target of an operation that
required that the target not exist.</p>
</li>
<li><p><code>EISDIR</code> (Is a directory): An operation expected a file, but the given
pathname was a directory.</p>
</li>
<li><p><code>EMFILE</code> (Too many open files in system): Maximum number of
<a href="https://en.wikipedia.org/wiki/File_descriptor">file descriptors</a> allowable on the system has been reached, and
requests for another descriptor cannot be fulfilled until at least one
has been closed. This is encountered when opening many files at once in
parallel, especially on systems (in particular, OS X) where there is a low
file descriptor limit for processes. To remedy a low limit, run
<code>ulimit -n 2048</code> in the same shell that will run the Node.js process.</p>
</li>
<li><p><code>ENOENT</code> (No such file or directory): Commonly raised by <a href="fs.html"><code>fs</code></a> operations
to indicate that a component of the specified pathname does not exist -- no
entity (file or directory) could be found by the given path.</p>
</li>
<li><p><code>ENOTDIR</code> (Not a directory): A component of the given pathname existed, but
was not a directory as expected. Commonly raised by <a href="fs.html#fs_fs_readdir_path_callback"><code>fs.readdir</code></a>.</p>
</li>
<li><p><code>ENOTEMPTY</code> (Directory not empty): A directory with entries was the target
of an operation that requires an empty directory -- usually <a href="fs.html#fs_fs_unlink_path_callback"><code>fs.unlink</code></a>.</p>
</li>
<li><p><code>EPERM</code> (Operation not permitted): An attempt was made to perform an
operation that requires elevated privileges.</p>
</li>
<li><p><code>EPIPE</code> (Broken pipe): A write on a pipe, socket, or FIFO for which there is
no process to read the data. Commonly encountered at the <a href="net.html"><code>net</code></a> and
<a href="http.html"><code>http</code></a> layers, indicative that the remote side of the stream being
written to has been closed.</p>
</li>
<li><p><code>ETIMEDOUT</code> (Operation timed out): A connect or send request failed because
the connected party did not properly respond after a period of time. Usually
encountered by <a href="http.html"><code>http</code></a> or <a href="net.html"><code>net</code></a> -- often a sign that a <code>socket.end()</code>
was not properly called.</p>
</li>
</ul>
<!-- [end-include:errors.md] -->
<!-- [start-include:events.md] -->
<h1>Events<span><a class="mark" href="#events_events" id="events_events">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><!--type=module-->
<p>Much of the Node.js core API is built around an idiomatic asynchronous
event-driven architecture in which certain kinds of objects (called "emitters")
periodically emit named events that cause Function objects ("listeners") to be
called.</p>
<p>For instance: a <a href="net.html#net_class_net_server"><code>net.Server</code></a> object emits an event each time a peer
connects to it; a <a href="fs.html#fs_class_fs_readstream"><code>fs.ReadStream</code></a> emits an event when the file is opened;
a <a href="stream.html#stream_stream">stream</a> emits an event whenever data is available to be read.</p>
<p>All objects that emit events are instances of the <code>EventEmitter</code> class. These
objects expose an <code>eventEmitter.on()</code> function that allows one or more
Functions to be attached to named events emitted by the object. Typically,
event names are camel-cased strings but any valid JavaScript property key
can be used.</p>
<p>When the <code>EventEmitter</code> object emits an event, all of the Functions attached
to that specific event are called <em>synchronously</em>. Any values returned by the
called listeners are <em>ignored</em> and will be discarded.</p>
<p>The following example shows a simple <code>EventEmitter</code> instance with a single
listener. The <code>eventEmitter.on()</code> method is used to register listeners, while
the <code>eventEmitter.emit()</code> method is used to trigger the event.</p>
<pre><code class="lang-js">const EventEmitter = require('events');
const util = require('util');
function MyEmitter() {
EventEmitter.call(this);
}
util.inherits(MyEmitter, EventEmitter);
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');
</code></pre>
<p>Any object can become an <code>EventEmitter</code> through inheritance. The example above
uses the traditional Node.js style prototypical inheritance using
the <code>util.inherits()</code> method. It is, however, possible to use ES6 classes as
well:</p>
<pre><code class="lang-js">const EventEmitter = require('events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');
</code></pre>
<h2>Passing arguments and <code>this</code> to listeners<span><a class="mark" href="#events_passing_arguments_and_this_to_listeners" id="events_passing_arguments_and_this_to_listeners">#</a></span></h2>
<p>The <code>eventEmitter.emit()</code> method allows an arbitrary set of arguments to be
passed to the listener functions. It is important to keep in mind that when an
ordinary listener function is called by the <code>EventEmitter</code>, the standard <code>this</code>
keyword is intentionally set to reference the <code>EventEmitter</code> to which the
listener is attached.</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
myEmitter.on('event', function(a, b) {
console.log(a, b, this);
// Prints:
// a b MyEmitter {
// domain: null,
// _events: { event: [Function] },
// _eventsCount: 1,
// _maxListeners: undefined }
});
myEmitter.emit('event', 'a', 'b');
</code></pre>
<p>It is possible to use ES6 Arrow Functions as listeners, however, when doing so,
the <code>this</code> keyword will no longer reference the <code>EventEmitter</code> instance:</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
console.log(a, b, this);
// Prints: a b {}
});
myEmitter.emit('event', 'a', 'b');
</code></pre>
<h2>Asynchronous vs. Synchronous<span><a class="mark" href="#events_asynchronous_vs_synchronous" id="events_asynchronous_vs_synchronous">#</a></span></h2>
<p>The <code>EventListener</code> calls all listeners synchronously in the order in which
they were registered. This is important to ensure the proper sequencing of
events and to avoid race conditions or logic errors. When appropriate,
listener functions can switch to an asynchronous mode of operation using
the <code>setImmediate()</code> or <code>process.nextTick()</code> methods:</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
setImmediate(() => {
console.log('this happens asynchronously');
});
});
myEmitter.emit('event', 'a', 'b');
</code></pre>
<h2>Handling events only once<span><a class="mark" href="#events_handling_events_only_once" id="events_handling_events_only_once">#</a></span></h2>
<p>When a listener is registered using the <code>eventEmitter.on()</code> method, that
listener will be invoked <em>every time</em> the named event is emitted.</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
var m = 0;
myEmitter.on('event', () => {
console.log(++m);
});
myEmitter.emit('event');
// Prints: 1
myEmitter.emit('event');
// Prints: 2
</code></pre>
<p>Using the <code>eventEmitter.once()</code> method, it is possible to register a listener
that is unregistered before it is called.</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
var m = 0;
myEmitter.once('event', () => {
console.log(++m);
});
myEmitter.emit('event');
// Prints: 1
myEmitter.emit('event');
// Ignored
</code></pre>
<h2>Error events<span><a class="mark" href="#events_error_events" id="events_error_events">#</a></span></h2>
<p>When an error occurs within an <code>EventEmitter</code> instance, the typical action is
for an <code>'error'</code> event to be emitted. These are treated as a special case
within Node.js.</p>
<p>If an <code>EventEmitter</code> does <em>not</em> have at least one listener registered for the
<code>'error'</code> event, and an <code>'error'</code> event is emitted, the error is thrown, a
stack trace is printed, and the Node.js process exits.</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
myEmitter.emit('error', new Error('whoops!'));
// Throws and crashes Node.js
</code></pre>
<p>To guard against crashing the Node.js process, developers can either register
a listener for the <code>process.on('uncaughtException')</code> event or use the
<a href="domain.html"><code>domain</code></a> module (<em>Note, however, that the <code>domain</code> module has been
deprecated</em>).</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
process.on('uncaughtException', (err) => {
console.log('whoops! there was an error');
});
myEmitter.emit('error', new Error('whoops!'));
// Prints: whoops! there was an error
</code></pre>
<p>As a best practice, developers should always register listeners for the
<code>'error'</code> event:</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
myEmitter.on('error', (err) => {
console.log('whoops! there was an error');
});
myEmitter.emit('error', new Error('whoops!'));
// Prints: whoops! there was an error
</code></pre>
<h2>Class: EventEmitter<span><a class="mark" href="#events_class_eventemitter" id="events_class_eventemitter">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.26</span>
</div><p>The <code>EventEmitter</code> class is defined and exposed by the <code>events</code> module:</p>
<pre><code class="lang-js">const EventEmitter = require('events');
</code></pre>
<p>All EventEmitters emit the event <code>'newListener'</code> when new listeners are
added and <code>'removeListener'</code> when a listener is removed.</p>
<h3>Event: 'newListener'<span><a class="mark" href="#events_event_newlistener" id="events_event_newlistener">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.26</span>
</div><ul>
<li><code>eventName</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><Symbol></a> The name of the event being listened for</li>
<li><code>listener</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The event handler function</li>
</ul>
<p>The <code>EventEmitter</code> instance will emit it's own <code>'newListener'</code> event <em>before</em>
a listener is added to it's internal array of listeners.</p>
<p>Listeners registered for the <code>'newListener'</code> event will be passed the event
name and a reference to the listener being added.</p>
<p>The fact that the event is triggered before adding the listener has a subtle
but important side effect: any <em>additional</em> listeners registered to the same
<code>name</code> <em>within</em> the <code>'newListener'</code> callback will be inserted <em>before</em> the
listener that is in the process of being added.</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
// Only do this once so we don't loop forever
myEmitter.once('newListener', (event, listener) => {
if (event === 'event') {
// Insert a new listener in front
myEmitter.on('event', () => {
console.log('B');
});
}
});
myEmitter.on('event', () => {
console.log('A');
});
myEmitter.emit('event');
// Prints:
// B
// A
</code></pre>
<h3>Event: 'removeListener'<span><a class="mark" href="#events_event_removelistener" id="events_event_removelistener">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.3</span>
</div><ul>
<li><code>eventName</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><Symbol></a> The event name</li>
<li><code>listener</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The event handler function</li>
</ul>
<p>The <code>'removeListener'</code> event is emitted <em>after</em> a listener is removed.</p>
<h3>EventEmitter.listenerCount(emitter, eventName)<span><a class="mark" href="#events_eventemitter_listenercount_emitter_eventname" id="events_eventemitter_listenercount_emitter_eventname">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.12</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="#events_emitter_listenercount_event"><code>emitter.listenerCount()</code></a> instead.</pre><p>A class method that returns the number of listeners for the given <code>eventName</code>
registered on the given <code>emitter</code>.</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(EventEmitter.listenerCount(myEmitter, 'event'));
// Prints: 2
</code></pre>
<h3>EventEmitter.defaultMaxListeners<span><a class="mark" href="#events_eventemitter_defaultmaxlisteners" id="events_eventemitter_defaultmaxlisteners">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.2</span>
</div><p>By default, a maximum of <code>10</code> listeners can be registered for any single
event. This limit can be changed for individual <code>EventEmitter</code> instances
using the <a href="#events_emitter_setmaxlisteners_n"><code>emitter.setMaxListeners(n)</code></a> method. To change the default
for <em>all</em> <code>EventEmitter</code> instances, the <code>EventEmitter.defaultMaxListeners</code>
property can be used.</p>
<p>Take caution when setting the <code>EventEmitter.defaultMaxListeners</code> because the
change effects <em>all</em> <code>EventEmitter</code> instances, including those created before
the change is made. However, calling <a href="#events_emitter_setmaxlisteners_n"><code>emitter.setMaxListeners(n)</code></a> still has
precedence over <code>EventEmitter.defaultMaxListeners</code>.</p>
<p>Note that this is not a hard limit. The <code>EventEmitter</code> instance will allow
more listeners to be added but will output a trace warning to stderr indicating
that a <code>possible EventEmitter memory leak</code> has been detected. For any single
<code>EventEmitter</code>, the <code>emitter.getMaxListeners()</code> and <code>emitter.setMaxListeners()</code>
methods can be used to temporarily avoid this warning:</p>
<pre><code class="lang-js">emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
// do stuff
emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});
</code></pre>
<h3>emitter.addListener(eventName, listener)<span><a class="mark" href="#events_emitter_addlistener_eventname_listener" id="events_emitter_addlistener_eventname_listener">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.26</span>
</div><p>Alias for <code>emitter.on(eventName, listener)</code>.</p>
<h3>emitter.emit(eventName[, arg1][, arg2][, ...])<span><a class="mark" href="#events_emitter_emit_eventname_arg1_arg2" id="events_emitter_emit_eventname_arg1_arg2">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.26</span>
</div><p>Synchronously calls each of the listeners registered for the event named
<code>eventName</code>, in the order they were registered, passing the supplied arguments
to each.</p>
<p>Returns <code>true</code> if the event had listeners, <code>false</code> otherwise.</p>
<h3>emitter.getMaxListeners()<span><a class="mark" href="#events_emitter_getmaxlisteners" id="events_emitter_getmaxlisteners">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><p>Returns the current max listener value for the <code>EventEmitter</code> which is either
set by <a href="#events_emitter_setmaxlisteners_n"><code>emitter.setMaxListeners(n)</code></a> or defaults to
<a href="#events_eventemitter_defaultmaxlisteners"><code>EventEmitter.defaultMaxListeners</code></a>.</p>
<h3>emitter.listenerCount(eventName)<span><a class="mark" href="#events_emitter_listenercount_eventname" id="events_emitter_listenercount_eventname">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v3.2.0</span>
</div><ul>
<li><code>eventName</code> <span class="type"><Value></span> The name of the event being listened for</li>
</ul>
<p>Returns the number of listeners listening to the event named <code>eventName</code>.</p>
<h3>emitter.listeners(eventName)<span><a class="mark" href="#events_emitter_listeners_eventname" id="events_emitter_listeners_eventname">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.26</span>
</div><p>Returns a copy of the array of listeners for the event named <code>eventName</code>.</p>
<pre><code class="lang-js">server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
</code></pre>
<h3>emitter.on(eventName, listener)<span><a class="mark" href="#events_emitter_on_eventname_listener" id="events_emitter_on_eventname_listener">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.101</span>
</div><p>Adds the <code>listener</code> function to the end of the listeners array for the
event named <code>eventName</code>. No checks are made to see if the <code>listener</code> has
already been added. Multiple calls passing the same combination of <code>eventName</code>
and <code>listener</code> will result in the <code>listener</code> being added, and called, multiple
times.</p>
<pre><code class="lang-js">server.on('connection', (stream) => {
console.log('someone connected!');
});
</code></pre>
<p>Returns a reference to the <code>EventEmitter</code> so calls can be chained.</p>
<h3>emitter.once(eventName, listener)<span><a class="mark" href="#events_emitter_once_eventname_listener" id="events_emitter_once_eventname_listener">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>Adds a <strong>one time</strong> <code>listener</code> function for the event named <code>eventName</code>. The
next time <code>eventName</code> is triggered, this listener is removed and then invoked.</p>
<pre><code class="lang-js">server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
</code></pre>
<p>Returns a reference to the <code>EventEmitter</code> so calls can be chained.</p>
<h3>emitter.removeAllListeners([eventName])<span><a class="mark" href="#events_emitter_removealllisteners_eventname" id="events_emitter_removealllisteners_eventname">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.26</span>
</div><p>Removes all listeners, or those of the specified <code>eventName</code>.</p>
<p>Note that it is bad practice to remove listeners added elsewhere in the code,
particularly when the <code>EventEmitter</code> instance was created by some other
component or module (e.g. sockets or file streams).</p>
<p>Returns a reference to the <code>EventEmitter</code> so calls can be chained.</p>
<h3>emitter.removeListener(eventName, listener)<span><a class="mark" href="#events_emitter_removelistener_eventname_listener" id="events_emitter_removelistener_eventname_listener">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.26</span>
</div><p>Removes the specified <code>listener</code> from the listener array for the event named
<code>eventName</code>.</p>
<pre><code class="lang-js">var callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
</code></pre>
<p><code>removeListener</code> will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified <code>eventName</code>, then <code>removeListener</code> must be
called multiple times to remove each instance.</p>
<p>Note that once an event has been emitted, all listeners attached to it at the
time of emitting will be called in order. This implies that any <code>removeListener()</code>
or <code>removeAllListeners()</code> calls <em>after</em> emitting and <em>before</em> the last listener
finishes execution will not remove them from <code>emit()</code> in progress. Subsequent
events will behave as expected.</p>
<pre><code class="lang-js">const myEmitter = new MyEmitter();
var callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
var callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
</code></pre>
<p>Because listeners are managed using an internal array, calling this will
change the position indices of any listener registered <em>after</em> the listener
being removed. This will not impact the order in which listeners are called,
but it will means that any copies of the listener array as returned by
the <code>emitter.listeners()</code> method will need to be recreated.</p>
<p>Returns a reference to the <code>EventEmitter</code> so calls can be chained.</p>
<h3>emitter.setMaxListeners(n)<span><a class="mark" href="#events_emitter_setmaxlisteners_n" id="events_emitter_setmaxlisteners_n">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.5</span>
</div><p>By default EventEmitters will print a warning if more than <code>10</code> listeners are
added for a particular event. This is a useful default that helps finding
memory leaks. Obviously, not all events should be limited to just 10 listeners.
The <code>emitter.setMaxListeners()</code> method allows the limit to be modified for this
specific <code>EventEmitter</code> instance. The value can be set to <code>Infinity</code> (or <code>0</code>)
to indicate an unlimited number of listeners.</p>
<p>Returns a reference to the <code>EventEmitter</code> so calls can be chained.</p>
<!-- [end-include:events.md] -->
<!-- [start-include:fs.md] -->
<h1>File System<span><a class="mark" href="#fs_file_system" id="fs_file_system">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><!--name=fs-->
<p>File I/O is provided by simple wrappers around standard POSIX functions. To
use this module do <code>require('fs')</code>. All the methods have asynchronous and
synchronous forms.</p>
<p>The asynchronous form always takes a completion callback as its last argument.
The arguments passed to the completion callback depend on the method, but the
first argument is always reserved for an exception. If the operation was
completed successfully, then the first argument will be <code>null</code> or <code>undefined</code>.</p>
<p>When using the synchronous form any exceptions are immediately thrown.
You can use try/catch to handle exceptions or allow them to bubble up.</p>
<p>Here is an example of the asynchronous version:</p>
<pre><code class="lang-js">const fs = require('fs');
fs.unlink('/tmp/hello', (err) => {
if (err) throw err;
console.log('successfully deleted /tmp/hello');
});
</code></pre>
<p>Here is the synchronous version:</p>
<pre><code class="lang-js">const fs = require('fs');
fs.unlinkSync('/tmp/hello');
console.log('successfully deleted /tmp/hello');
</code></pre>
<p>With the asynchronous methods there is no guaranteed ordering. So the
following is prone to error:</p>
<pre><code class="lang-js">fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
console.log('renamed complete');
});
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
</code></pre>
<p>It could be that <code>fs.stat</code> is executed before <code>fs.rename</code>.
The correct way to do this is to chain the callbacks.</p>
<pre><code class="lang-js">fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
});
</code></pre>
<p>In busy processes, the programmer is <em>strongly encouraged</em> to use the
asynchronous versions of these calls. The synchronous versions will block
the entire process until they complete--halting all connections.</p>
<p>The relative path to a filename can be used. Remember, however, that this path
will be relative to <code>process.cwd()</code>.</p>
<p>Most fs functions let you omit the callback argument. If you do, a default
callback is used that rethrows errors. To get a trace to the original call
site, set the <code>NODE_DEBUG</code> environment variable:</p>
<pre><code>$ cat script.js
function bad() {
require('fs').readFile('/');
}
bad();
$ env NODE_DEBUG=fs node script.js
fs.js:66
throw err;
^
Error: EISDIR, read
at rethrow (fs.js:61:21)
at maybeCallback (fs.js:79:42)
at Object.fs.readFile (fs.js:153:18)
at bad (/path/to/script.js:2:17)
at Object.<anonymous> (/path/to/script.js:5:1)
<etc.>
</code></pre><h2>Class: fs.FSWatcher<span><a class="mark" href="#fs_class_fs_fswatcher" id="fs_class_fs_fswatcher">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Objects returned from <code>fs.watch()</code> are of this type.</p>
<h3>Event: 'change'<span><a class="mark" href="#fs_event_change" id="fs_event_change">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><ul>
<li><code>event</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The type of fs change</li>
<li><code>filename</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The filename that changed (if relevant/available)</li>
</ul>
<p>Emitted when something changes in a watched directory or file.
See more details in <a href="#fs_fs_watch_filename_options_listener"><code>fs.watch()</code></a>.</p>
<h3>Event: 'error'<span><a class="mark" href="#fs_event_error" id="fs_event_error">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><ul>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Emitted when an error occurs.</p>
<h3>watcher.close()<span><a class="mark" href="#fs_watcher_close" id="fs_watcher_close">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Stop watching for changes on the given <code>fs.FSWatcher</code>.</p>
<h2>Class: fs.ReadStream<span><a class="mark" href="#fs_class_fs_readstream" id="fs_class_fs_readstream">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.93</span>
</div><p><code>ReadStream</code> is a <a href="stream.html#stream_class_stream_readable">Readable Stream</a>.</p>
<h3>Event: 'open'<span><a class="mark" href="#fs_event_open" id="fs_event_open">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.93</span>
</div><ul>
<li><code>fd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Integer file descriptor used by the ReadStream.</li>
</ul>
<p>Emitted when the ReadStream's file is opened.</p>
<h3>Event: 'close'<span><a class="mark" href="#fs_event_close" id="fs_event_close">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.93</span>
</div><p>Emitted when the <code>ReadStream</code>'s underlying file descriptor has been closed
using the <code>fs.close()</code> method.</p>
<h3>readStream.path<span><a class="mark" href="#fs_readstream_path" id="fs_readstream_path">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.93</span>
</div><p>The path to the file the stream is reading from.</p>
<h2>Class: fs.Stats<span><a class="mark" href="#fs_class_fs_stats" id="fs_class_fs_stats">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Objects returned from <a href="#fs_fs_stat_path_callback"><code>fs.stat()</code></a>, <a href="#fs_fs_lstat_path_callback"><code>fs.lstat()</code></a> and <a href="#fs_fs_fstat_fd_callback"><code>fs.fstat()</code></a> and their
synchronous counterparts are of this type.</p>
<ul>
<li><code>stats.isFile()</code></li>
<li><code>stats.isDirectory()</code></li>
<li><code>stats.isBlockDevice()</code></li>
<li><code>stats.isCharacterDevice()</code></li>
<li><code>stats.isSymbolicLink()</code> (only valid with <a href="#fs_fs_lstat_path_callback"><code>fs.lstat()</code></a>)</li>
<li><code>stats.isFIFO()</code></li>
<li><code>stats.isSocket()</code></li>
</ul>
<p>For a regular file <a href="util.html#util_util_inspect_object_options"><code>util.inspect(stats)</code></a> would return a string very
similar to this:</p>
<pre><code class="lang-js">{
dev: 2114,
ino: 48064969,
mode: 33188,
nlink: 1,
uid: 85,
gid: 100,
rdev: 0,
size: 527,
blksize: 4096,
blocks: 8,
atime: Mon, 10 Oct 2011 23:24:11 GMT,
mtime: Mon, 10 Oct 2011 23:24:11 GMT,
ctime: Mon, 10 Oct 2011 23:24:11 GMT,
birthtime: Mon, 10 Oct 2011 23:24:11 GMT
}
</code></pre>
<p>Please note that <code>atime</code>, <code>mtime</code>, <code>birthtime</code>, and <code>ctime</code> are
instances of <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date"><code>Date</code></a> object and to compare the values of
these objects you should use appropriate methods. For most general
uses <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/getTime"><code>getTime()</code></a> will return the number of
milliseconds elapsed since <em>1 January 1970 00:00:00 UTC</em> and this
integer should be sufficient for any comparison, however there are
additional methods which can be used for displaying fuzzy information.
More details can be found in the <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date">MDN JavaScript Reference</a>
page.</p>
<h3>Stat Time Values<span><a class="mark" href="#fs_stat_time_values" id="fs_stat_time_values">#</a></span></h3>
<p>The times in the stat object have the following semantics:</p>
<ul>
<li><code>atime</code> "Access Time" - Time when file data last accessed. Changed
by the <a href="http://man7.org/linux/man-pages/man2/mknod.2.html">mknod(2)</a>, <a href="http://man7.org/linux/man-pages/man2/utimes.2.html">utimes(2)</a>, and <a href="http://man7.org/linux/man-pages/man2/read.2.html">read(2)</a> system calls.</li>
<li><code>mtime</code> "Modified Time" - Time when file data last modified.
Changed by the <a href="http://man7.org/linux/man-pages/man2/mknod.2.html">mknod(2)</a>, <a href="http://man7.org/linux/man-pages/man2/utimes.2.html">utimes(2)</a>, and <a href="http://man7.org/linux/man-pages/man2/write.2.html">write(2)</a> system calls.</li>
<li><code>ctime</code> "Change Time" - Time when file status was last changed
(inode data modification). Changed by the <a href="http://man7.org/linux/man-pages/man2/chmod.2.html">chmod(2)</a>, <a href="http://man7.org/linux/man-pages/man2/chown.2.html">chown(2)</a>,
link(2), <a href="http://man7.org/linux/man-pages/man2/mknod.2.html">mknod(2)</a>, <a href="http://man7.org/linux/man-pages/man2/rename.2.html">rename(2)</a>, <a href="http://man7.org/linux/man-pages/man2/unlink.2.html">unlink(2)</a>, <a href="http://man7.org/linux/man-pages/man2/utimes.2.html">utimes(2)</a>,
read(2), and <a href="http://man7.org/linux/man-pages/man2/write.2.html">write(2)</a> system calls.</li>
<li><code>birthtime</code> "Birth Time" - Time of file creation. Set once when the
file is created. On filesystems where birthtime is not available,
this field may instead hold either the <code>ctime</code> or
<code>1970-01-01T00:00Z</code> (ie, unix epoch timestamp <code>0</code>). Note that this
value may be greater than <code>atime</code> or <code>mtime</code> in this case. On Darwin
and other FreeBSD variants, also set if the <code>atime</code> is explicitly
set to an earlier value than the current <code>birthtime</code> using the
utimes(2) system call.</li>
</ul>
<p>Prior to Node v0.12, the <code>ctime</code> held the <code>birthtime</code> on Windows
systems. Note that as of v0.12, <code>ctime</code> is not "creation time", and
on Unix systems, it never was.</p>
<h2>Class: fs.WriteStream<span><a class="mark" href="#fs_class_fs_writestream" id="fs_class_fs_writestream">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.93</span>
</div><p><code>WriteStream</code> is a <a href="stream.html#stream_class_stream_writable">Writable Stream</a>.</p>
<h3>Event: 'open'<span><a class="mark" href="#fs_event_open_1" id="fs_event_open_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.93</span>
</div><ul>
<li><code>fd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Integer file descriptor used by the WriteStream.</li>
</ul>
<p>Emitted when the WriteStream's file is opened.</p>
<h3>Event: 'close'<span><a class="mark" href="#fs_event_close_1" id="fs_event_close_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.93</span>
</div><p>Emitted when the <code>WriteStream</code>'s underlying file descriptor has been closed
using the <code>fs.close()</code> method.</p>
<h3>writeStream.bytesWritten<span><a class="mark" href="#fs_writestream_byteswritten" id="fs_writestream_byteswritten">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.4.7</span>
</div><p>The number of bytes written so far. Does not include data that is still queued
for writing.</p>
<h3>writeStream.path<span><a class="mark" href="#fs_writestream_path" id="fs_writestream_path">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.93</span>
</div><p>The path to the file the stream is writing to.</p>
<h2>fs.access(path[, mode], callback)<span><a class="mark" href="#fs_fs_access_path_mode_callback" id="fs_fs_access_path_mode_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.15</span>
</div><p>Tests a user's permissions for the file specified by <code>path</code>. <code>mode</code> is an
optional integer that specifies the accessibility checks to be performed. The
following constants define the possible values of <code>mode</code>. It is possible to
create a mask consisting of the bitwise OR of two or more values.</p>
<ul>
<li><code>fs.F_OK</code> - File is visible to the calling process. This is useful for
determining if a file exists, but says nothing about <code>rwx</code> permissions.
Default if no <code>mode</code> is specified.</li>
<li><code>fs.R_OK</code> - File can be read by the calling process.</li>
<li><code>fs.W_OK</code> - File can be written by the calling process.</li>
<li><code>fs.X_OK</code> - File can be executed by the calling process. This has no effect
on Windows (will behave like <code>fs.F_OK</code>).</li>
</ul>
<p>The final argument, <code>callback</code>, is a callback function that is invoked with
a possible error argument. If any of the accessibility checks fail, the error
argument will be populated. The following example checks if the file
<code>/etc/passwd</code> can be read and written by the current process.</p>
<pre><code class="lang-js">fs.access('/etc/passwd', fs.R_OK | fs.W_OK, (err) => {
console.log(err ? 'no access!' : 'can read/write');
});
</code></pre>
<p>Using <code>fs.access()</code> to check for the accessibility of a file before calling
<code>fs.open()</code>, <code>fs.readFile()</code> or <code>fs.writeFile()</code> is not recommended. Doing
so introduces a race condition, since other processes may change the file's
state between the two calls. Instead, user code should open/read/write the
file directly and handle the error raised if the file is not accessible.</p>
<p>For example:</p>
<p><strong>write (NOT RECOMMENDED)</strong></p>
<pre><code class="lang-js">fs.access('myfile', (err) => {
if (!err) {
console.error('myfile already exists');
return;
}
fs.open('myfile', 'wx', (err, fd) => {
if (err) throw err;
writeMyData(fd);
});
});
</code></pre>
<p><strong>write (RECOMMENDED)</strong></p>
<pre><code class="lang-js">fs.open('myfile', 'wx', (err, fd) => {
if (err) {
if (err.code === "EEXIST") {
console.error('myfile already exists');
return;
} else {
throw err;
}
}
writeMyData(fd);
});
</code></pre>
<p><strong>read (NOT RECOMMENDED)</strong></p>
<pre><code class="lang-js">fs.access('myfile', (err) => {
if (err) {
if (err.code === "ENOENT") {
console.error('myfile does not exist');
return;
} else {
throw err;
}
}
fs.open('myfile', 'r', (err, fd) => {
if (err) throw err;
readMyData(fd);
});
});
</code></pre>
<p><strong>read (RECOMMENDED)</strong></p>
<pre><code class="lang-js">fs.open('myfile', 'r', (err, fd) => {
if (err) {
if (err.code === "ENOENT") {
console.error('myfile does not exist');
return;
} else {
throw err;
}
}
readMyData(fd);
});
</code></pre>
<p>The "not recommended" examples above check for accessibility and then use the
file; the "recommended" examples are better because they use the file directly
and handle the error, if any.</p>
<p>In general, check for the accessibility of a file only if the file won’t be
used directly, for example when its accessibility is a signal from another
process.</p>
<h2>fs.accessSync(path[, mode])<span><a class="mark" href="#fs_fs_accesssync_path_mode" id="fs_fs_accesssync_path_mode">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.15</span>
</div><p>Synchronous version of <a href="#fs_fs_access_path_mode_callback"><code>fs.access()</code></a>. This throws if any accessibility checks
fail, and does nothing otherwise.</p>
<h2>fs.appendFile(file, data[, options], callback)<span><a class="mark" href="#fs_fs_appendfile_file_data_options_callback" id="fs_fs_appendfile_file_data_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.7</span>
</div><ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> filename</li>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a><ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><Null></a> default = <code>'utf8'</code></li>
<li><code>mode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> default = <code>0o666</code></li>
<li><code>flag</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> default = <code>'a'</code></li>
</ul>
</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Asynchronously append data to a file, creating the file if it does not yet exist.
<code>data</code> can be a string or a buffer.</p>
<p>Example:</p>
<pre><code class="lang-js">fs.appendFile('message.txt', 'data to append', (err) => {
if (err) throw err;
console.log('The "data to append" was appended to file!');
});
</code></pre>
<p>If <code>options</code> is a string, then it specifies the encoding. Example:</p>
<pre><code class="lang-js">fs.appendFile('message.txt', 'data to append', 'utf8', callback);
</code></pre>
<h2>fs.appendFileSync(file, data[, options])<span><a class="mark" href="#fs_fs_appendfilesync_file_data_options" id="fs_fs_appendfilesync_file_data_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.7</span>
</div><p>The synchronous version of <a href="fs.html#fs_fs_appendfile_file_data_options_callback"><code>fs.appendFile()</code></a>. Returns <code>undefined</code>.</p>
<h2>fs.chmod(path, mode, callback)<span><a class="mark" href="#fs_fs_chmod_path_mode_callback" id="fs_fs_chmod_path_mode_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.30</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/chmod.2.html">chmod(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.chmodSync(path, mode)<span><a class="mark" href="#fs_fs_chmodsync_path_mode" id="fs_fs_chmodsync_path_mode">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.7</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/chmod.2.html">chmod(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.chown(path, uid, gid, callback)<span><a class="mark" href="#fs_fs_chown_path_uid_gid_callback" id="fs_fs_chown_path_uid_gid_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.97</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/chown.2.html">chown(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.chownSync(path, uid, gid)<span><a class="mark" href="#fs_fs_chownsync_path_uid_gid" id="fs_fs_chownsync_path_uid_gid">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.97</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/chown.2.html">chown(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.close(fd, callback)<span><a class="mark" href="#fs_fs_close_fd_callback" id="fs_fs_close_fd_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/close.2.html">close(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.closeSync(fd)<span><a class="mark" href="#fs_fs_closesync_fd" id="fs_fs_closesync_fd">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/close.2.html">close(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.createReadStream(path[, options])<span><a class="mark" href="#fs_fs_createreadstream_path_options" id="fs_fs_createreadstream_path_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Returns a new <a href="#fs_class_fs_readstream"><code>ReadStream</code></a> object. (See <a href="stream.html#stream_class_stream_readable">Readable Stream</a>).</p>
<p>Be aware that, unlike the default value set for <code>highWaterMark</code> on a
readable stream (16 kb), the stream returned by this method has a
default value of 64 kb for the same parameter.</p>
<p><code>options</code> is an object or string with the following defaults:</p>
<pre><code class="lang-js">{
flags: 'r',
encoding: null,
fd: null,
mode: 0o666,
autoClose: true
}
</code></pre>
<p><code>options</code> can include <code>start</code> and <code>end</code> values to read a range of bytes from
the file instead of the entire file. Both <code>start</code> and <code>end</code> are inclusive and
start counting at 0. If <code>fd</code> is specified and <code>start</code> is omitted or <code>undefined</code>,
<code>fs.createReadStream()</code> reads sequentially from the current file position.
The <code>encoding</code> can be any one of those accepted by <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<p>If <code>fd</code> is specified, <code>ReadStream</code> will ignore the <code>path</code> argument and will use
the specified file descriptor. This means that no <code>'open'</code> event will be emitted.
Note that <code>fd</code> should be blocking; non-blocking <code>fd</code>s should be passed to
<a href="net.html#net_class_net_socket"><code>net.Socket</code></a>.</p>
<p>If <code>autoClose</code> is false, then the file descriptor won't be closed, even if
there's an error. It is your responsibility to close it and make sure
there's no file descriptor leak. If <code>autoClose</code> is set to true (default
behavior), on <code>error</code> or <code>end</code> the file descriptor will be closed
automatically.</p>
<p><code>mode</code> sets the file mode (permission and sticky bits), but only if the
file was created.</p>
<p>An example to read the last 10 bytes of a file which is 100 bytes long:</p>
<pre><code class="lang-js">fs.createReadStream('sample.txt', {start: 90, end: 99});
</code></pre>
<p>If <code>options</code> is a string, then it specifies the encoding.</p>
<h2>fs.createWriteStream(path[, options])<span><a class="mark" href="#fs_fs_createwritestream_path_options" id="fs_fs_createwritestream_path_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Returns a new <a href="#fs_class_fs_writestream"><code>WriteStream</code></a> object. (See <a href="stream.html#stream_class_stream_writable">Writable Stream</a>).</p>
<p><code>options</code> is an object or string with the following defaults:</p>
<pre><code class="lang-js">{
flags: 'w',
defaultEncoding: 'utf8',
fd: null,
mode: 0o666
}
</code></pre>
<p><code>options</code> may also include a <code>start</code> option to allow writing data at
some position past the beginning of the file. Modifying a file rather
than replacing it may require a <code>flags</code> mode of <code>r+</code> rather than the
default mode <code>w</code>. The <code>defaultEncoding</code> can be any one of those accepted by <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>.</p>
<p>Like <a href="#fs_class_fs_readstream"><code>ReadStream</code></a>, if <code>fd</code> is specified, <code>WriteStream</code> will ignore the
<code>path</code> argument and will use the specified file descriptor. This means that no
<code>'open'</code> event will be emitted. Note that <code>fd</code> should be blocking; non-blocking
<code>fd</code>s should be passed to <a href="net.html#net_class_net_socket"><code>net.Socket</code></a>.</p>
<p>If <code>options</code> is a string, then it specifies the encoding.</p>
<h2>fs.exists(path, callback)<span><a class="mark" href="#fs_fs_exists_path_callback" id="fs_fs_exists_path_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
<span>Deprecated since: v1.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="#fs_fs_stat_path_callback"><code>fs.stat()</code></a> or <a href="#fs_fs_access_path_mode_callback"><code>fs.access()</code></a> instead.</pre><p>Test whether or not the given path exists by checking with the file system.
Then call the <code>callback</code> argument with either true or false. Example:</p>
<pre><code class="lang-js">fs.exists('/etc/passwd', (exists) => {
console.log(exists ? 'it\'s there' : 'no passwd!');
});
</code></pre>
<p>Using <code>fs.exists()</code> to check for the existence of a file before calling
<code>fs.open()</code>, <code>fs.readFile()</code> or <code>fs.writeFile()</code> is not recommended. Doing
so introduces a race condition, since other processes may change the file's
state between the two calls. Instead, user code should open/read/write the
file directly and handle the error raised if the file does not exist.</p>
<p>For example:</p>
<p><strong>write (NOT RECOMMENDED)</strong></p>
<pre><code class="lang-js">fs.exists('myfile', (exists) => {
if (exists) {
console.error('myfile already exists');
} else {
fs.open('myfile', 'wx', (err, fd) => {
if (err) throw err;
writeMyData(fd);
});
}
});
</code></pre>
<p><strong>write (RECOMMENDED)</strong></p>
<pre><code class="lang-js">fs.open('myfile', 'wx', (err, fd) => {
if (err) {
if (err.code === "EEXIST") {
console.error('myfile already exists');
return;
} else {
throw err;
}
}
writeMyData(fd);
});
</code></pre>
<p><strong>read (NOT RECOMMENDED)</strong></p>
<pre><code class="lang-js">fs.exists('myfile', (exists) => {
if (exists) {
fs.open('myfile', 'r', (err, fd) => {
readMyData(fd);
});
} else {
console.error('myfile does not exist');
}
});
</code></pre>
<p><strong>read (RECOMMENDED)</strong></p>
<pre><code class="lang-js">fs.open('myfile', 'r', (err, fd) => {
if (err) {
if (err.code === "ENOENT") {
console.error('myfile does not exist');
return;
} else {
throw err;
}
} else {
readMyData(fd);
}
});
</code></pre>
<p>The "not recommended" examples above check for existence and then use the
file; the "recommended" examples are better because they use the file directly
and handle the error, if any.</p>
<p>In general, check for the existence of a file only if the file won’t be
used directly, for example when its existence is a signal from another
process.</p>
<h2>fs.existsSync(path)<span><a class="mark" href="#fs_fs_existssync_path" id="fs_fs_existssync_path">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
<span>Deprecated since: v1.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="#fs_fs_statsync_path"><code>fs.statSync()</code></a> or <a href="#fs_fs_accesssync_path_mode"><code>fs.accessSync()</code></a> instead.</pre><p>Synchronous version of <a href="fs.html#fs_fs_exists_path_callback"><code>fs.exists()</code></a>.
Returns <code>true</code> if the file exists, <code>false</code> otherwise.</p>
<h2>fs.fchmod(fd, mode, callback)<span><a class="mark" href="#fs_fs_fchmod_fd_mode_callback" id="fs_fs_fchmod_fd_mode_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.7</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/fchmod.2.html">fchmod(2)</a>. No arguments other than a possible exception
are given to the completion callback.</p>
<h2>fs.fchmodSync(fd, mode)<span><a class="mark" href="#fs_fs_fchmodsync_fd_mode" id="fs_fs_fchmodsync_fd_mode">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.7</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/fchmod.2.html">fchmod(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.fchown(fd, uid, gid, callback)<span><a class="mark" href="#fs_fs_fchown_fd_uid_gid_callback" id="fs_fs_fchown_fd_uid_gid_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.7</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/fchown.2.html">fchown(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.fchownSync(fd, uid, gid)<span><a class="mark" href="#fs_fs_fchownsync_fd_uid_gid" id="fs_fs_fchownsync_fd_uid_gid">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.7</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/fchown.2.html">fchown(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.fdatasync(fd, callback)<span><a class="mark" href="#fs_fs_fdatasync_fd_callback" id="fs_fs_fdatasync_fd_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.96</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/fdatasync.2.html">fdatasync(2)</a>. No arguments other than a possible exception are
given to the completion callback.</p>
<h2>fs.fdatasyncSync(fd)<span><a class="mark" href="#fs_fs_fdatasyncsync_fd" id="fs_fs_fdatasyncsync_fd">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.96</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/fdatasync.2.html">fdatasync(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.fstat(fd, callback)<span><a class="mark" href="#fs_fs_fstat_fd_callback" id="fs_fs_fstat_fd_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.95</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/fstat.2.html">fstat(2)</a>. The callback gets two arguments <code>(err, stats)</code> where
<code>stats</code> is a <a href="#fs_class_fs_stats"><code>fs.Stats</code></a> object. <code>fstat()</code> is identical to <a href="fs.html#fs_fs_stat_path_callback"><code>stat()</code></a>,
except that the file to be stat-ed is specified by the file descriptor <code>fd</code>.</p>
<h2>fs.fstatSync(fd)<span><a class="mark" href="#fs_fs_fstatsync_fd" id="fs_fs_fstatsync_fd">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.95</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/fstat.2.html">fstat(2)</a>. Returns an instance of <code>fs.Stats</code>.</p>
<h2>fs.fsync(fd, callback)<span><a class="mark" href="#fs_fs_fsync_fd_callback" id="fs_fs_fsync_fd_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.96</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/fsync.2.html">fsync(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.fsyncSync(fd)<span><a class="mark" href="#fs_fs_fsyncsync_fd" id="fs_fs_fsyncsync_fd">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.96</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/fsync.2.html">fsync(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.ftruncate(fd, len, callback)<span><a class="mark" href="#fs_fs_ftruncate_fd_len_callback" id="fs_fs_ftruncate_fd_len_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.8.6</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/ftruncate.2.html">ftruncate(2)</a>. No arguments other than a possible exception are
given to the completion callback.</p>
<h2>fs.ftruncateSync(fd, len)<span><a class="mark" href="#fs_fs_ftruncatesync_fd_len" id="fs_fs_ftruncatesync_fd_len">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.8.6</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/ftruncate.2.html">ftruncate(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.futimes(fd, atime, mtime, callback)<span><a class="mark" href="#fs_fs_futimes_fd_atime_mtime_callback" id="fs_fs_futimes_fd_atime_mtime_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.2</span>
</div><p>Change the file timestamps of a file referenced by the supplied file
descriptor.</p>
<h2>fs.futimesSync(fd, atime, mtime)<span><a class="mark" href="#fs_fs_futimessync_fd_atime_mtime" id="fs_fs_futimessync_fd_atime_mtime">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.2</span>
</div><p>Synchronous version of <a href="#fs_fs_futimes_fd_atime_mtime_callback"><code>fs.futimes()</code></a>. Returns <code>undefined</code>.</p>
<h2>fs.lchmod(path, mode, callback)<span><a class="mark" href="#fs_fs_lchmod_path_mode_callback" id="fs_fs_lchmod_path_mode_callback">#</a></span></h2>
<div class="api_metadata">
<span>Deprecated since: v0.4.7 </span>
</div><p>Asynchronous <a href="https://www.freebsd.org/cgi/man.cgi?query=lchmod&sektion=2">lchmod(2)</a>. No arguments other than a possible exception
are given to the completion callback.</p>
<p>Only available on Mac OS X.</p>
<h2>fs.lchmodSync(path, mode)<span><a class="mark" href="#fs_fs_lchmodsync_path_mode" id="fs_fs_lchmodsync_path_mode">#</a></span></h2>
<div class="api_metadata">
<span>Deprecated since: v0.4.7 </span>
</div><p>Synchronous <a href="https://www.freebsd.org/cgi/man.cgi?query=lchmod&sektion=2">lchmod(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.lchown(path, uid, gid, callback)<span><a class="mark" href="#fs_fs_lchown_path_uid_gid_callback" id="fs_fs_lchown_path_uid_gid_callback">#</a></span></h2>
<div class="api_metadata">
<span>Deprecated since: v0.4.7 </span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/lchown.2.html">lchown(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.lchownSync(path, uid, gid)<span><a class="mark" href="#fs_fs_lchownsync_path_uid_gid" id="fs_fs_lchownsync_path_uid_gid">#</a></span></h2>
<div class="api_metadata">
<span>Deprecated since: v0.4.7 </span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/lchown.2.html">lchown(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.link(srcpath, dstpath, callback)<span><a class="mark" href="#fs_fs_link_srcpath_dstpath_callback" id="fs_fs_link_srcpath_dstpath_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/link.2.html">link(2)</a>. No arguments other than a possible exception are given to
the completion callback.</p>
<h2>fs.linkSync(srcpath, dstpath)<span><a class="mark" href="#fs_fs_linksync_srcpath_dstpath" id="fs_fs_linksync_srcpath_dstpath">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/link.2.html">link(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.lstat(path, callback)<span><a class="mark" href="#fs_fs_lstat_path_callback" id="fs_fs_lstat_path_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.30</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/lstat.2.html">lstat(2)</a>. The callback gets two arguments <code>(err, stats)</code> where
<code>stats</code> is a <a href="#fs_class_fs_stats"><code>fs.Stats</code></a> object. <code>lstat()</code> is identical to <code>stat()</code>,
except that if <code>path</code> is a symbolic link, then the link itself is stat-ed,
not the file that it refers to.</p>
<h2>fs.lstatSync(path)<span><a class="mark" href="#fs_fs_lstatsync_path" id="fs_fs_lstatsync_path">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.30</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/lstat.2.html">lstat(2)</a>. Returns an instance of <code>fs.Stats</code>.</p>
<h2>fs.mkdir(path[, mode], callback)<span><a class="mark" href="#fs_fs_mkdir_path_mode_callback" id="fs_fs_mkdir_path_mode_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.8</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/mkdir.2.html">mkdir(2)</a>. No arguments other than a possible exception are given
to the completion callback. <code>mode</code> defaults to <code>0o777</code>.</p>
<h2>fs.mkdirSync(path[, mode])<span><a class="mark" href="#fs_fs_mkdirsync_path_mode" id="fs_fs_mkdirsync_path_mode">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/mkdir.2.html">mkdir(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.mkdtemp(prefix, callback)<span><a class="mark" href="#fs_fs_mkdtemp_prefix_callback" id="fs_fs_mkdtemp_prefix_callback">#</a></span></h2>
<p>Creates a unique temporary directory.</p>
<p>Generates six random characters to be appended behind a required
<code>prefix</code> to create a unique temporary directory.</p>
<p>The created folder path is passed as a string to the callback's second
parameter.</p>
<p>Example:</p>
<pre><code class="lang-js">fs.mkdtemp('/tmp/foo-', (err, folder) => {
console.log(folder);
// Prints: /tmp/foo-itXde2
});
</code></pre>
<h2>fs.mkdtempSync(template)<span><a class="mark" href="#fs_fs_mkdtempsync_template" id="fs_fs_mkdtempsync_template">#</a></span></h2>
<p>The synchronous version of [<code>fs.mkdtemp()</code>][]. Returns the created
folder path.</p>
<h2>fs.open(path, flags[, mode], callback)<span><a class="mark" href="#fs_fs_open_path_flags_mode_callback" id="fs_fs_open_path_flags_mode_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Asynchronous file open. See <a href="http://man7.org/linux/man-pages/man2/open.2.html">open(2)</a>. <code>flags</code> can be:</p>
<ul>
<li><p><code>'r'</code> - Open file for reading.
An exception occurs if the file does not exist.</p>
</li>
<li><p><code>'r+'</code> - Open file for reading and writing.
An exception occurs if the file does not exist.</p>
</li>
<li><p><code>'rs'</code> - Open file for reading in synchronous mode. Instructs the operating
system to bypass the local file system cache.</p>
<p>This is primarily useful for opening files on NFS mounts as it allows you to
skip the potentially stale local cache. It has a very real impact on I/O
performance so don't use this flag unless you need it.</p>
<p>Note that this doesn't turn <code>fs.open()</code> into a synchronous blocking call.
If that's what you want then you should be using <code>fs.openSync()</code></p>
</li>
<li><p><code>'rs+'</code> - Open file for reading and writing, telling the OS to open it
synchronously. See notes for <code>'rs'</code> about using this with caution.</p>
</li>
<li><p><code>'w'</code> - Open file for writing.
The file is created (if it does not exist) or truncated (if it exists).</p>
</li>
<li><p><code>'wx'</code> - Like <code>'w'</code> but fails if <code>path</code> exists.</p>
</li>
<li><p><code>'w+'</code> - Open file for reading and writing.
The file is created (if it does not exist) or truncated (if it exists).</p>
</li>
<li><p><code>'wx+'</code> - Like <code>'w+'</code> but fails if <code>path</code> exists.</p>
</li>
<li><p><code>'a'</code> - Open file for appending.
The file is created if it does not exist.</p>
</li>
<li><p><code>'ax'</code> - Like <code>'a'</code> but fails if <code>path</code> exists.</p>
</li>
<li><p><code>'a+'</code> - Open file for reading and appending.
The file is created if it does not exist.</p>
</li>
<li><p><code>'ax+'</code> - Like <code>'a+'</code> but fails if <code>path</code> exists.</p>
</li>
</ul>
<p><code>mode</code> sets the file mode (permission and sticky bits), but only if the file was
created. It defaults to <code>0666</code>, readable and writable.</p>
<p>The callback gets two arguments <code>(err, fd)</code>.</p>
<p>The exclusive flag <code>'x'</code> (<code>O_EXCL</code> flag in <a href="http://man7.org/linux/man-pages/man2/open.2.html">open(2)</a>) ensures that <code>path</code> is newly
created. On POSIX systems, <code>path</code> is considered to exist even if it is a symlink
to a non-existent file. The exclusive flag may or may not work with network file
systems.</p>
<p><code>flags</code> can also be a number as documented by <a href="http://man7.org/linux/man-pages/man2/open.2.html">open(2)</a>; commonly used constants
are available from <code>require('constants')</code>. On Windows, flags are translated to
their equivalent ones where applicable, e.g. <code>O_WRONLY</code> to <code>FILE_GENERIC_WRITE</code>,
or <code>O_EXCL|O_CREAT</code> to <code>CREATE_NEW</code>, as accepted by CreateFileW.</p>
<p>On Linux, positional writes don't work when the file is opened in append mode.
The kernel ignores the position argument and always appends the data to
the end of the file.</p>
<h2>fs.openSync(path, flags[, mode])<span><a class="mark" href="#fs_fs_opensync_path_flags_mode" id="fs_fs_opensync_path_flags_mode">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous version of <a href="#fs_fs_open_path_flags_mode_callback"><code>fs.open()</code></a>. Returns an integer representing the file
descriptor.</p>
<h2>fs.read(fd, buffer, offset, length, position, callback)<span><a class="mark" href="#fs_fs_read_fd_buffer_offset_length_position_callback" id="fs_fs_read_fd_buffer_offset_length_position_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Read data from the file specified by <code>fd</code>.</p>
<p><code>buffer</code> is the buffer that the data will be written to.</p>
<p><code>offset</code> is the offset in the buffer to start writing at.</p>
<p><code>length</code> is an integer specifying the number of bytes to read.</p>
<p><code>position</code> is an integer specifying where to begin reading from in the file.
If <code>position</code> is <code>null</code>, data will be read from the current file position.</p>
<p>The callback is given the three arguments, <code>(err, bytesRead, buffer)</code>.</p>
<h2>fs.readdir(path, callback)<span><a class="mark" href="#fs_fs_readdir_path_callback" id="fs_fs_readdir_path_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.8</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man3/readdir.3.html">readdir(3)</a>. Reads the contents of a directory.
The callback gets two arguments <code>(err, files)</code> where <code>files</code> is an array of
the names of the files in the directory excluding <code>'.'</code> and <code>'..'</code>.</p>
<h2>fs.readdirSync(path)<span><a class="mark" href="#fs_fs_readdirsync_path" id="fs_fs_readdirsync_path">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man3/readdir.3.html">readdir(3)</a>. Returns an array of filenames excluding <code>'.'</code> and
<code>'..'</code>.</p>
<h2>fs.readFile(file[, options], callback)<span><a class="mark" href="#fs_fs_readfile_file_options_callback" id="fs_fs_readfile_file_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.29</span>
</div><ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> filename</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a><ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><Null></a> default = <code>null</code></li>
<li><code>flag</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> default = <code>'r'</code></li>
</ul>
</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Asynchronously reads the entire contents of a file. Example:</p>
<pre><code class="lang-js">fs.readFile('/etc/passwd', (err, data) => {
if (err) throw err;
console.log(data);
});
</code></pre>
<p>The callback is passed two arguments <code>(err, data)</code>, where <code>data</code> is the
contents of the file.</p>
<p>If no encoding is specified, then the raw buffer is returned.</p>
<p>If <code>options</code> is a string, then it specifies the encoding. Example:</p>
<pre><code class="lang-js">fs.readFile('/etc/passwd', 'utf8', callback);
</code></pre>
<h2>fs.readFileSync(file[, options])<span><a class="mark" href="#fs_fs_readfilesync_file_options" id="fs_fs_readfilesync_file_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.8</span>
</div><p>Synchronous version of <a href="#fs_fs_readfile_file_options_callback"><code>fs.readFile</code></a>. Returns the contents of the <code>file</code>.</p>
<p>If the <code>encoding</code> option is specified then this function returns a
string. Otherwise it returns a buffer.</p>
<h2>fs.readlink(path, callback)<span><a class="mark" href="#fs_fs_readlink_path_callback" id="fs_fs_readlink_path_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/readlink.2.html">readlink(2)</a>. The callback gets two arguments <code>(err,
linkString)</code>.</p>
<h2>fs.readlinkSync(path)<span><a class="mark" href="#fs_fs_readlinksync_path" id="fs_fs_readlinksync_path">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/readlink.2.html">readlink(2)</a>. Returns the symbolic link's string value.</p>
<h2>fs.realpath(path[, cache], callback)<span><a class="mark" href="#fs_fs_realpath_path_cache_callback" id="fs_fs_realpath_path_cache_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/realpath.2.html">realpath(2)</a>. The <code>callback</code> gets two arguments <code>(err,
resolvedPath)</code>. May use <code>process.cwd</code> to resolve relative paths. <code>cache</code> is an
object literal of mapped paths that can be used to force a specific path
resolution or avoid additional <code>fs.stat</code> calls for known real paths.</p>
<p>Example:</p>
<pre><code class="lang-js">var cache = {'/etc':'/private/etc'};
fs.realpath('/etc/passwd', cache, (err, resolvedPath) => {
if (err) throw err;
console.log(resolvedPath);
});
</code></pre>
<h2>fs.readSync(fd, buffer, offset, length, position)<span><a class="mark" href="#fs_fs_readsync_fd_buffer_offset_length_position" id="fs_fs_readsync_fd_buffer_offset_length_position">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous version of <a href="#fs_fs_read_fd_buffer_offset_length_position_callback"><code>fs.read()</code></a>. Returns the number of <code>bytesRead</code>.</p>
<h2>fs.realpathSync(path[, cache])<span><a class="mark" href="#fs_fs_realpathsync_path_cache" id="fs_fs_realpathsync_path_cache">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/realpath.2.html">realpath(2)</a>. Returns the resolved path. <code>cache</code> is an
object literal of mapped paths that can be used to force a specific path
resolution or avoid additional <code>fs.stat</code> calls for known real paths.</p>
<h2>fs.rename(oldPath, newPath, callback)<span><a class="mark" href="#fs_fs_rename_oldpath_newpath_callback" id="fs_fs_rename_oldpath_newpath_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/rename.2.html">rename(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.renameSync(oldPath, newPath)<span><a class="mark" href="#fs_fs_renamesync_oldpath_newpath" id="fs_fs_renamesync_oldpath_newpath">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/rename.2.html">rename(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.rmdir(path, callback)<span><a class="mark" href="#fs_fs_rmdir_path_callback" id="fs_fs_rmdir_path_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/rmdir.2.html">rmdir(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.rmdirSync(path)<span><a class="mark" href="#fs_fs_rmdirsync_path" id="fs_fs_rmdirsync_path">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/rmdir.2.html">rmdir(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.stat(path, callback)<span><a class="mark" href="#fs_fs_stat_path_callback" id="fs_fs_stat_path_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/stat.2.html">stat(2)</a>. The callback gets two arguments <code>(err, stats)</code> where
<code>stats</code> is a <a href="#fs_class_fs_stats"><code>fs.Stats</code></a> object. See the <a href="#fs_class_fs_stats"><code>fs.Stats</code></a> section for more
information.</p>
<h2>fs.statSync(path)<span><a class="mark" href="#fs_fs_statsync_path" id="fs_fs_statsync_path">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/stat.2.html">stat(2)</a>. Returns an instance of <a href="#fs_class_fs_stats"><code>fs.Stats</code></a>.</p>
<h2>fs.symlink(target, path[, type], callback)<span><a class="mark" href="#fs_fs_symlink_target_path_type_callback" id="fs_fs_symlink_target_path_type_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/symlink.2.html">symlink(2)</a>. No arguments other than a possible exception are given
to the completion callback.
The <code>type</code> argument can be set to <code>'dir'</code>, <code>'file'</code>, or <code>'junction'</code> (default
is <code>'file'</code>) and is only available on Windows (ignored on other platforms).
Note that Windows junction points require the destination path to be absolute. When using
<code>'junction'</code>, the <code>target</code> argument will automatically be normalized to absolute path.</p>
<p>Here is an example below:</p>
<pre><code class="lang-js">fs.symlink('./foo', './new-port');
</code></pre>
<p>It creates a symbolic link named "new-port" that points to "foo".</p>
<h2>fs.symlinkSync(target, path[, type])<span><a class="mark" href="#fs_fs_symlinksync_target_path_type" id="fs_fs_symlinksync_target_path_type">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/symlink.2.html">symlink(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.truncate(path, len, callback)<span><a class="mark" href="#fs_fs_truncate_path_len_callback" id="fs_fs_truncate_path_len_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.8.6</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/truncate.2.html">truncate(2)</a>. No arguments other than a possible exception are
given to the completion callback. A file descriptor can also be passed as the
first argument. In this case, <code>fs.ftruncate()</code> is called.</p>
<h2>fs.truncateSync(path, len)<span><a class="mark" href="#fs_fs_truncatesync_path_len" id="fs_fs_truncatesync_path_len">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.8.6</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/truncate.2.html">truncate(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.unlink(path, callback)<span><a class="mark" href="#fs_fs_unlink_path_callback" id="fs_fs_unlink_path_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Asynchronous <a href="http://man7.org/linux/man-pages/man2/unlink.2.html">unlink(2)</a>. No arguments other than a possible exception are given
to the completion callback.</p>
<h2>fs.unlinkSync(path)<span><a class="mark" href="#fs_fs_unlinksync_path" id="fs_fs_unlinksync_path">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><p>Synchronous <a href="http://man7.org/linux/man-pages/man2/unlink.2.html">unlink(2)</a>. Returns <code>undefined</code>.</p>
<h2>fs.unwatchFile(filename[, listener])<span><a class="mark" href="#fs_fs_unwatchfile_filename_listener" id="fs_fs_unwatchfile_filename_listener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Stop watching for changes on <code>filename</code>. If <code>listener</code> is specified, only that
particular listener is removed. Otherwise, <em>all</em> listeners are removed and you
have effectively stopped watching <code>filename</code>.</p>
<p>Calling <code>fs.unwatchFile()</code> with a filename that is not being watched is a
no-op, not an error.</p>
<p><em>Note: <a href="#fs_fs_watch_filename_options_listener"><code>fs.watch()</code></a> is more efficient than <code>fs.watchFile()</code> and <code>fs.unwatchFile()</code>.
<code>fs.watch()</code> should be used instead of <code>fs.watchFile()</code> and <code>fs.unwatchFile()</code>
when possible.</em></p>
<h2>fs.utimes(path, atime, mtime, callback)<span><a class="mark" href="#fs_fs_utimes_path_atime_mtime_callback" id="fs_fs_utimes_path_atime_mtime_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.2</span>
</div><p>Change file timestamps of the file referenced by the supplied path.</p>
<p>Note: the arguments <code>atime</code> and <code>mtime</code> of the following related functions does
follow the below rules:</p>
<ul>
<li>If the value is a numberable string like <code>'123456789'</code>, the value would get
converted to corresponding number.</li>
<li>If the value is <code>NaN</code> or <code>Infinity</code>, the value would get converted to
<code>Date.now()</code>.</li>
</ul>
<h2>fs.utimesSync(path, atime, mtime)<span><a class="mark" href="#fs_fs_utimessync_path_atime_mtime" id="fs_fs_utimessync_path_atime_mtime">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.2</span>
</div><p>Synchronous version of <a href="#fs_fs_futimes_fd_atime_mtime_callback"><code>fs.utimes()</code></a>. Returns <code>undefined</code>.</p>
<h2>fs.watch(filename[, options][, listener])<span><a class="mark" href="#fs_fs_watch_filename_options_listener" id="fs_fs_watch_filename_options_listener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.10</span>
</div><p>Watch for changes on <code>filename</code>, where <code>filename</code> is either a file or a
directory. The returned object is a <a href="#fs_class_fs_fswatcher"><code>fs.FSWatcher</code></a>.</p>
<p>The second argument is optional. The <code>options</code> if provided should be an object.
The supported boolean members are <code>persistent</code> and <code>recursive</code>. <code>persistent</code>
indicates whether the process should continue to run as long as files are being
watched. <code>recursive</code> indicates whether all subdirectories should be watched, or
only the current directory. This applies when a directory is specified, and only
on supported platforms (See <a href="#fs_caveats">Caveats</a>).</p>
<p>The default is <code>{ persistent: true, recursive: false }</code>.</p>
<p>The listener callback gets two arguments <code>(event, filename)</code>. <code>event</code> is either
<code>'rename'</code> or <code>'change'</code>, and <code>filename</code> is the name of the file which triggered
the event.</p>
<h3>Caveats<span><a class="mark" href="#fs_caveats" id="fs_caveats">#</a></span></h3>
<!--type=misc-->
<p>The <code>fs.watch</code> API is not 100% consistent across platforms, and is
unavailable in some situations.</p>
<p>The recursive option is only supported on OS X and Windows.</p>
<h4>Availability<span><a class="mark" href="#fs_availability" id="fs_availability">#</a></span></h4>
<!--type=misc-->
<p>This feature depends on the underlying operating system providing a way
to be notified of filesystem changes.</p>
<ul>
<li>On Linux systems, this uses <code>inotify</code>.</li>
<li>On BSD systems, this uses <code>kqueue</code>.</li>
<li>On OS X, this uses <code>kqueue</code> for files and 'FSEvents' for directories.</li>
<li>On SunOS systems (including Solaris and SmartOS), this uses <code>event ports</code>.</li>
<li>On Windows systems, this feature depends on <code>ReadDirectoryChangesW</code>.</li>
<li>On Aix systems, this feature depends on <code>AHAFS</code>, which must be enabled.</li>
</ul>
<p>If the underlying functionality is not available for some reason, then
<code>fs.watch</code> will not be able to function. For example, watching files or
directories can be unreliable, and in some cases impossible, on network file
systems (NFS, SMB, etc), or host file systems when using virtualization software
such as Vagrant, Docker, etc.</p>
<p>You can still use <code>fs.watchFile</code>, which uses stat polling, but it is slower and
less reliable.</p>
<h4>Inodes<span><a class="mark" href="#fs_inodes" id="fs_inodes">#</a></span></h4>
<!--type=misc-->
<p>On Linux and OS X systems, <code>fs.watch()</code> resolves the path to an <a href="http://www.linux.org/threads/intro-to-inodes.4130">inode</a> and
watches the inode. If the watched path is deleted and recreated, it is assigned
a new inode. The watch will emit an event for the delete but will continue
watching the <em>original</em> inode. Events for the new inode will not be emitted.
This is expected behavior.</p>
<h4>Filename Argument<span><a class="mark" href="#fs_filename_argument" id="fs_filename_argument">#</a></span></h4>
<!--type=misc-->
<p>Providing <code>filename</code> argument in the callback is only supported on Linux and
Windows. Even on supported platforms, <code>filename</code> is not always guaranteed to
be provided. Therefore, don't assume that <code>filename</code> argument is always
provided in the callback, and have some fallback logic if it is null.</p>
<pre><code class="lang-js">fs.watch('somedir', (event, filename) => {
console.log(`event is: ${event}`);
if (filename) {
console.log(`filename provided: ${filename}`);
} else {
console.log('filename not provided');
}
});
</code></pre>
<h2>fs.watchFile(filename[, options], listener)<span><a class="mark" href="#fs_fs_watchfile_filename_options_listener" id="fs_fs_watchfile_filename_options_listener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Watch for changes on <code>filename</code>. The callback <code>listener</code> will be called each
time the file is accessed.</p>
<p>The <code>options</code> argument may be omitted. If provided, it should be an object. The
<code>options</code> object may contain a boolean named <code>persistent</code> that indicates
whether the process should continue to run as long as files are being watched.
The <code>options</code> object may specify an <code>interval</code> property indicating how often the
target should be polled in milliseconds. The default is
<code>{ persistent: true, interval: 5007 }</code>.</p>
<p>The <code>listener</code> gets two arguments the current stat object and the previous
stat object:</p>
<pre><code class="lang-js">fs.watchFile('message.text', (curr, prev) => {
console.log(`the current mtime is: ${curr.mtime}`);
console.log(`the previous mtime was: ${prev.mtime}`);
});
</code></pre>
<p>These stat objects are instances of <code>fs.Stat</code>.</p>
<p>If you want to be notified when the file was modified, not just accessed,
you need to compare <code>curr.mtime</code> and <code>prev.mtime</code>.</p>
<p><em>Note: when an <code>fs.watchFile</code> operation results in an <code>ENOENT</code> error, it will
invoke the listener once, with all the fields zeroed (or, for dates, the Unix
Epoch). In Windows, <code>blksize</code> and <code>blocks</code> fields will be <code>undefined</code>, instead
of zero. If the file is created later on, the listener will be called again,
with the latest stat objects. This is a change in functionality since v0.10.</em></p>
<p><em>Note: <a href="#fs_fs_watch_filename_options_listener"><code>fs.watch()</code></a> is more efficient than <code>fs.watchFile</code> and <code>fs.unwatchFile</code>.
<code>fs.watch</code> should be used instead of <code>fs.watchFile</code> and <code>fs.unwatchFile</code>
when possible.</em></p>
<h2>fs.write(fd, buffer, offset, length[, position], callback)<span><a class="mark" href="#fs_fs_write_fd_buffer_offset_length_position_callback" id="fs_fs_write_fd_buffer_offset_length_position_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Write <code>buffer</code> to the file specified by <code>fd</code>.</p>
<p><code>offset</code> determines the part of the buffer to be written, and <code>length</code> is
an integer specifying the number of bytes to write.</p>
<p><code>position</code> refers to the offset from the beginning of the file where this data
should be written. If <code>typeof position !== 'number'</code>, the data will be written
at the current position. See <a href="http://man7.org/linux/man-pages/man2/pwrite.2.html">pwrite(2)</a>.</p>
<p>The callback will be given three arguments <code>(err, written, buffer)</code> where
<code>written</code> specifies how many <em>bytes</em> were written from <code>buffer</code>.</p>
<p>Note that it is unsafe to use <code>fs.write</code> multiple times on the same file
without waiting for the callback. For this scenario,
<code>fs.createWriteStream</code> is strongly recommended.</p>
<p>On Linux, positional writes don't work when the file is opened in append mode.
The kernel ignores the position argument and always appends the data to
the end of the file.</p>
<h2>fs.write(fd, data[, position[, encoding]], callback)<span><a class="mark" href="#fs_fs_write_fd_data_position_encoding_callback" id="fs_fs_write_fd_data_position_encoding_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
</div><p>Write <code>data</code> to the file specified by <code>fd</code>. If <code>data</code> is not a Buffer instance
then the value will be coerced to a string.</p>
<p><code>position</code> refers to the offset from the beginning of the file where this data
should be written. If <code>typeof position !== 'number'</code> the data will be written at
the current position. See <a href="http://man7.org/linux/man-pages/man2/pwrite.2.html">pwrite(2)</a>.</p>
<p><code>encoding</code> is the expected string encoding.</p>
<p>The callback will receive the arguments <code>(err, written, string)</code> where <code>written</code>
specifies how many <em>bytes</em> the passed string required to be written. Note that
bytes written is not the same as string characters. See <a href="buffer.html#buffer_class_method_buffer_bytelength_string_encoding"><code>Buffer.byteLength</code></a>.</p>
<p>Unlike when writing <code>buffer</code>, the entire string must be written. No substring
may be specified. This is because the byte offset of the resulting data may not
be the same as the string offset.</p>
<p>Note that it is unsafe to use <code>fs.write</code> multiple times on the same file
without waiting for the callback. For this scenario,
<code>fs.createWriteStream</code> is strongly recommended.</p>
<p>On Linux, positional writes don't work when the file is opened in append mode.
The kernel ignores the position argument and always appends the data to
the end of the file.</p>
<h2>fs.writeFile(file, data[, options], callback)<span><a class="mark" href="#fs_fs_writefile_file_data_options_callback" id="fs_fs_writefile_file_data_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.29</span>
</div><ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> filename</li>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a><ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><Null></a> default = <code>'utf8'</code></li>
<li><code>mode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> default = <code>0o666</code></li>
<li><code>flag</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> default = <code>'w'</code></li>
</ul>
</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Asynchronously writes data to a file, replacing the file if it already exists.
<code>data</code> can be a string or a buffer.</p>
<p>The <code>encoding</code> option is ignored if <code>data</code> is a buffer. It defaults
to <code>'utf8'</code>.</p>
<p>Example:</p>
<pre><code class="lang-js">fs.writeFile('message.txt', 'Hello Node.js', (err) => {
if (err) throw err;
console.log('It\'s saved!');
});
</code></pre>
<p>If <code>options</code> is a string, then it specifies the encoding. Example:</p>
<pre><code class="lang-js">fs.writeFile('message.txt', 'Hello Node.js', 'utf8', callback);
</code></pre>
<p>Note that it is unsafe to use <code>fs.writeFile</code> multiple times on the same file
without waiting for the callback. For this scenario,
<code>fs.createWriteStream</code> is strongly recommended.</p>
<h2>fs.writeFileSync(file, data[, options])<span><a class="mark" href="#fs_fs_writefilesync_file_data_options" id="fs_fs_writefilesync_file_data_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.29</span>
</div><p>The synchronous version of <a href="#fs_fs_writefile_file_data_options_callback"><code>fs.writeFile()</code></a>. Returns <code>undefined</code>.</p>
<h2>fs.writeSync(fd, buffer, offset, length[, position])<span><a class="mark" href="#fs_fs_writesync_fd_buffer_offset_length_position" id="fs_fs_writesync_fd_buffer_offset_length_position">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div><h2>fs.writeSync(fd, data[, position[, encoding]])<span><a class="mark" href="#fs_fs_writesync_fd_data_position_encoding" id="fs_fs_writesync_fd_data_position_encoding">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
</div><p>Synchronous versions of <a href="#fs_fs_write_fd_buffer_offset_length_position_callback"><code>fs.write()</code></a>. Returns the number of bytes written.</p>
<!-- [end-include:fs.md] -->
<!-- [start-include:globals.md] -->
<h1>Global Objects<span><a class="mark" href="#globals_global_objects" id="globals_global_objects">#</a></span></h1>
<!-- type=misc -->
<p>These objects are available in all modules. Some of these objects aren't
actually in the global scope but in the module scope - this will be noted.</p>
<p>The objects listed here are specific to Node.js. There are a number of
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects">built-in objects</a> that are part of the JavaScript language itself, which are
also globally accessible.</p>
<h2>Class: Buffer<span><a class="mark" href="#globals_class_buffer" id="globals_class_buffer">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.103</span>
</div><!-- type=global -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Used to handle binary data. See the <a href="buffer.html">buffer section</a>.</p>
<h2>__dirname<span><a class="mark" href="#globals_dirname" id="globals_dirname">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.27</span>
</div><!-- type=var -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
<p>The directory name of the current module. This the same as the
<a href="path.html#path_path_dirname_path"><code>path.dirname()</code></a> of the <a href="#globals_filename"><code>__filename</code></a>.</p>
<p><code>__dirname</code> isn't actually a global but rather local to each module.</p>
<p>Example: running <code>node example.js</code> from <code>/Users/mjr</code></p>
<pre><code class="lang-js">console.log(__dirname);
// Prints: /Users/mjr
console.log(path.dirname(__filename));
// Prints: /Users/mjr
</code></pre>
<h2>__filename<span><a class="mark" href="#globals_filename" id="globals_filename">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><!-- type=var -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
<p>The file name of the current module. This is the resolved absolute path of the
current module file.</p>
<p>For a main program this is not necessarily the same as the file name used in the
command line.</p>
<p>See <a href="#globals_dirname"><code>__dirname</code></a> for the directory name of the current module.</p>
<p><code>__filename</code> isn't actually a global but rather local to each module.</p>
<p>Examples:</p>
<p>Running <code>node example.js</code> from <code>/Users/mjr</code></p>
<pre><code class="lang-js">console.log(__filename);
// Prints: /Users/mjr/example.js
console.log(__dirname);
// Prints: /Users/mjr
</code></pre>
<p>Given two modules: <code>a</code> and <code>b</code>, where <code>b</code> is a dependency of
<code>a</code> and there is a directory structure of:</p>
<ul>
<li><code>/Users/mjr/app/a.js</code></li>
<li><code>/Users/mjr/app/node_modules/b/b.js</code></li>
</ul>
<p>References to <code>__filename</code> within <code>b.js</code> will return
<code>/Users/mjr/app/node_modules/b/b.js</code> while references to <code>__filename</code> within
<code>a.js</code> will return <code>/Users/mjr/app/a.js</code>.</p>
<h2>clearImmediate(immediateObject)<span><a class="mark" href="#globals_clearimmediate_immediateobject" id="globals_clearimmediate_immediateobject">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><!--type=global-->
<p><a href="timers.html#timers_clearimmediate_immediateobject"><code>clearImmediate</code></a> is described in the <a href="timers.html">timers</a> section.</p>
<h2>clearInterval(intervalObject)<span><a class="mark" href="#globals_clearinterval_intervalobject" id="globals_clearinterval_intervalobject">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><!--type=global-->
<p><a href="timers.html#timers_clearinterval_intervalobject"><code>clearInterval</code></a> is described in the <a href="timers.html">timers</a> section.</p>
<h2>clearTimeout(timeoutObject)<span><a class="mark" href="#globals_cleartimeout_timeoutobject" id="globals_cleartimeout_timeoutobject">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><!--type=global-->
<p><a href="timers.html#timers_cleartimeout_timeoutobject"><code>clearTimeout</code></a> is described in the <a href="timers.html">timers</a> section.</p>
<h2>console<span><a class="mark" href="#globals_console" id="globals_console">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.100</span>
</div><!-- type=global -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Used to print to stdout and stderr. See the <a href="console.html"><code>console</code></a> section.</p>
<h2>exports<span><a class="mark" href="#globals_exports" id="globals_exports">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.12</span>
</div><!-- type=var -->
<p>A reference to the <code>module.exports</code> that is shorter to type.
See <a href="modules.html">module system documentation</a> for details on when to use <code>exports</code> and
when to use <code>module.exports</code>.</p>
<p><code>exports</code> isn't actually a global but rather local to each module.</p>
<p>See the <a href="modules.html">module system documentation</a> for more information.</p>
<h2>global<span><a class="mark" href="#globals_global" id="globals_global">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.27</span>
</div><!-- type=global -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The global namespace object.</li>
</ul>
<p>In browsers, the top-level scope is the global scope. That means that in
browsers if you're in the global scope <code>var something</code> will define a global
variable. In Node.js this is different. The top-level scope is not the global
scope; <code>var something</code> inside an Node.js module will be local to that module.</p>
<h2>module<span><a class="mark" href="#globals_module" id="globals_module">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><!-- type=var -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>A reference to the current module. In particular
<code>module.exports</code> is used for defining what a module exports and makes
available through <code>require()</code>.</p>
<p><code>module</code> isn't actually a global but rather local to each module.</p>
<p>See the <a href="modules.html">module system documentation</a> for more information.</p>
<h2>process<span><a class="mark" href="#globals_process" id="globals_process">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.7</span>
</div><!-- type=global -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>The process object. See the <a href="process.html#process_process"><code>process</code> object</a> section.</p>
<h2>require()<span><a class="mark" href="#globals_require" id="globals_require">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.13</span>
</div><!-- type=var -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>To require modules. See the <a href="modules.html#modules_modules">Modules</a> section. <code>require</code> isn't actually a
global but rather local to each module.</p>
<h3>require.cache<span><a class="mark" href="#globals_require_cache" id="globals_require_cache">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Modules are cached in this object when they are required. By deleting a key
value from this object, the next <code>require</code> will reload the module. Note that
this does not apply to <a href="addons.html">native addons</a>, for which reloading will result in an
Error.</p>
<h3>require.extensions<span><a class="mark" href="#globals_require_extensions" id="globals_require_extensions">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
<span>Deprecated since: v0.10.6 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Instruct <code>require</code> on how to handle certain file extensions.</p>
<p>Process files with the extension <code>.sjs</code> as <code>.js</code>:</p>
<pre><code class="lang-js">require.extensions['.sjs'] = require.extensions['.js'];
</code></pre>
<p><strong>Deprecated</strong> In the past, this list has been used to load
non-JavaScript modules into Node.js by compiling them on-demand.
However, in practice, there are much better ways to do this, such as
loading modules via some other Node.js program, or compiling them to
JavaScript ahead of time.</p>
<p>Since the Module system is locked, this feature will probably never go
away. However, it may have subtle bugs and complexities that are best
left untouched.</p>
<h3>require.resolve()<span><a class="mark" href="#globals_require_resolve" id="globals_require_resolve">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>Use the internal <code>require()</code> machinery to look up the location of a module,
but rather than loading the module, just return the resolved filename.</p>
<h2>setImmediate(callback[, arg][, ...])<span><a class="mark" href="#globals_setimmediate_callback_arg" id="globals_setimmediate_callback_arg">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><!-- type=global -->
<p><a href="timers.html#timers_setimmediate_callback_arg"><code>setImmediate</code></a> is described in the <a href="timers.html">timers</a> section.</p>
<h2>setInterval(callback, delay[, arg][, ...])<span><a class="mark" href="#globals_setinterval_callback_delay_arg" id="globals_setinterval_callback_delay_arg">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><!-- type=global -->
<p><a href="timers.html#timers_setinterval_callback_delay_arg"><code>setInterval</code></a> is described in the <a href="timers.html">timers</a> section.</p>
<h2>setTimeout(callback, delay[, arg][, ...])<span><a class="mark" href="#globals_settimeout_callback_delay_arg" id="globals_settimeout_callback_delay_arg">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><!-- type=global -->
<p><a href="timers.html#timers_settimeout_callback_delay_arg"><code>setTimeout</code></a> is described in the <a href="timers.html">timers</a> section.</p>
<!-- [end-include:globals.md] -->
<!-- [start-include:http.md] -->
<h1>HTTP<span><a class="mark" href="#http_http" id="http_http">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>To use the HTTP server and client one must <code>require('http')</code>.</p>
<p>The HTTP interfaces in Node.js are designed to support many features
of the protocol which have been traditionally difficult to use.
In particular, large, possibly chunk-encoded, messages. The interface is
careful to never buffer entire requests or responses--the
user is able to stream data.</p>
<p>HTTP message headers are represented by an object like this:</p>
<pre><code>{ 'content-length': '123',
'content-type': 'text/plain',
'connection': 'keep-alive',
'host': 'mysite.com',
'accept': '*/*' }
</code></pre><p>Keys are lowercased. Values are not modified.</p>
<p>In order to support the full spectrum of possible HTTP applications, Node.js's
HTTP API is very low-level. It deals with stream handling and message
parsing only. It parses a message into headers and body but it does not
parse the actual headers or the body.</p>
<p>See <a href="#http_message_headers"><code>message.headers</code></a> for details on how duplicate headers are handled.</p>
<p>The raw headers as they were received are retained in the <code>rawHeaders</code>
property, which is an array of <code>[key, value, key2, value2, ...]</code>. For
example, the previous message header object might have a <code>rawHeaders</code>
list like the following:</p>
<pre><code>[ 'ConTent-Length', '123456',
'content-LENGTH', '123',
'content-type', 'text/plain',
'CONNECTION', 'keep-alive',
'Host', 'mysite.com',
'accepT', '*/*' ]
</code></pre><h2>Class: http.Agent<span><a class="mark" href="#http_class_http_agent" id="http_class_http_agent">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><p>The HTTP Agent is used for pooling sockets used in HTTP client
requests.</p>
<p>The HTTP Agent also defaults client requests to using
Connection:keep-alive. If no pending HTTP requests are waiting on a
socket to become free the socket is closed. This means that Node.js's
pool has the benefit of keep-alive when under load but still does not
require developers to manually close the HTTP clients using
KeepAlive.</p>
<p>If you opt into using HTTP KeepAlive, you can create an Agent object
with that flag set to <code>true</code>. (See the <a href="#http_new_agent_options">constructor options</a>.)
Then, the Agent will keep unused sockets in a pool for later use. They
will be explicitly marked so as to not keep the Node.js process running.
However, it is still a good idea to explicitly <a href="#net_socket_destroy"><code>destroy()</code></a> KeepAlive
agents when they are no longer in use, so that the Sockets will be shut
down.</p>
<p>Sockets are removed from the agent's pool when the socket emits either
a <code>'close'</code> event or a special <code>'agentRemove'</code> event. This means that if
you intend to keep one HTTP request open for a long time and don't
want it to stay in the pool you can do something along the lines of:</p>
<pre><code class="lang-js">http.get(options, (res) => {
// Do stuff
}).on('socket', (socket) => {
socket.emit('agentRemove');
});
</code></pre>
<p>Alternatively, you could just opt out of pooling entirely using
<code>agent:false</code>:</p>
<pre><code class="lang-js">http.get({
hostname: 'localhost',
port: 80,
path: '/',
agent: false // create a new agent just for this one request
}, (res) => {
// Do stuff with response
})
</code></pre>
<h3>new Agent(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#http_new_agent_options" id="http_new_agent_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Set of configurable options to set on the agent.
Can have the following fields:<ul>
<li><code>keepAlive</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Keep sockets around even when there are no
outstanding requests, so they can be used for future requests without
having to reestablish a TCP connection. Default = <code>false</code></li>
<li><code>keepAliveMsecs</code> <span class="type"><Integer></span> When using the <code>keepAlive</code> option, specifies
the <a href="net.html#net_socket_setkeepalive_enable_initialdelay">initial delay</a>
for TCP Keep-Alive packets. Ignored when the
<code>keepAlive</code> option is <code>false</code> or <code>undefined</code>. Default = <code>1000</code>.</li>
<li><code>maxSockets</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Maximum number of sockets to allow per
host. Default = <code>Infinity</code>.</li>
<li><code>maxFreeSockets</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Maximum number of sockets to leave open
in a free state. Only relevant if <code>keepAlive</code> is set to <code>true</code>.
Default = <code>256</code>.</li>
</ul>
</li>
</ul>
<p>The default <a href="#http_http_globalagent"><code>http.globalAgent</code></a> that is used by <a href="http.html#http_http_request_options_callback"><code>http.request()</code></a> has all
of these values set to their respective defaults.</p>
<p>To configure any of them, you must create your own <a href="http.html#http_class_http_agent"><code>http.Agent</code></a> object.</p>
<pre><code class="lang-js">const http = require('http');
var keepAliveAgent = new http.Agent({ keepAlive: true });
options.agent = keepAliveAgent;
http.request(options, onResponseCallback);
</code></pre>
<h3>agent.destroy()<span><a class="mark" href="#http_agent_destroy" id="http_agent_destroy">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Destroy any sockets that are currently in use by the agent.</p>
<p>It is usually not necessary to do this. However, if you are using an
agent with KeepAlive enabled, then it is best to explicitly shut down
the agent when you know that it will no longer be used. Otherwise,
sockets may hang open for quite a long time before the server
terminates them.</p>
<h3>agent.freeSockets<span><a class="mark" href="#http_agent_freesockets" id="http_agent_freesockets">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>An object which contains arrays of sockets currently awaiting use by
the Agent when HTTP KeepAlive is used. Do not modify.</p>
<h3>agent.getName(options)<span><a class="mark" href="#http_agent_getname_options" id="http_agent_getname_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Get a unique name for a set of request options, to determine whether a
connection can be reused. In the http agent, this returns
<code>host:port:localAddress</code>. In the https agent, the name includes the
CA, cert, ciphers, and other HTTPS/TLS-specific options that determine
socket reusability.</p>
<p>Options:</p>
<ul>
<li><code>host</code>: A domain name or IP address of the server to issue the request to.</li>
<li><code>port</code>: Port of remote server.</li>
<li><code>localAddress</code>: Local interface to bind for network connections when issuing
the request.</li>
</ul>
<h3>agent.maxFreeSockets<span><a class="mark" href="#http_agent_maxfreesockets" id="http_agent_maxfreesockets">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.7</span>
</div><p>By default set to 256. For Agents supporting HTTP KeepAlive, this
sets the maximum number of sockets that will be left open in the free
state.</p>
<h3>agent.maxSockets<span><a class="mark" href="#http_agent_maxsockets" id="http_agent_maxsockets">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.6</span>
</div><p>By default set to Infinity. Determines how many concurrent sockets the agent
can have open per origin. Origin is either a 'host:port' or
'host:port:localAddress' combination.</p>
<h3>agent.requests<span><a class="mark" href="#http_agent_requests" id="http_agent_requests">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><p>An object which contains queues of requests that have not yet been assigned to
sockets. Do not modify.</p>
<h3>agent.sockets<span><a class="mark" href="#http_agent_sockets" id="http_agent_sockets">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.6</span>
</div><p>An object which contains arrays of sockets currently in use by the
Agent. Do not modify.</p>
<h2>Class: http.ClientRequest<span><a class="mark" href="#http_class_http_clientrequest" id="http_class_http_clientrequest">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.17</span>
</div><p>This object is created internally and returned from <a href="http.html#http_http_request_options_callback"><code>http.request()</code></a>. It
represents an <em>in-progress</em> request whose header has already been queued. The
header is still mutable using the <code>setHeader(name, value)</code>, <code>getHeader(name)</code>,
<code>removeHeader(name)</code> API. The actual header will be sent along with the first
data chunk or when closing the connection.</p>
<p>To get the response, add a listener for <code>'response'</code> to the request object.
<code>'response'</code> will be emitted from the request object when the response
headers have been received. The <code>'response'</code> event is executed with one
argument which is an instance of <a href="#http_class_http_incomingmessage"><code>http.IncomingMessage</code></a>.</p>
<p>During the <code>'response'</code> event, one can add listeners to the
response object; particularly to listen for the <code>'data'</code> event.</p>
<p>If no <code>'response'</code> handler is added, then the response will be
entirely discarded. However, if you add a <code>'response'</code> event handler,
then you <strong>must</strong> consume the data from the response object, either by
calling <code>response.read()</code> whenever there is a <code>'readable'</code> event, or
by adding a <code>'data'</code> handler, or by calling the <code>.resume()</code> method.
Until the data is consumed, the <code>'end'</code> event will not fire. Also, until
the data is read it will consume memory that can eventually lead to a
'process out of memory' error.</p>
<p>Note: Node.js does not check whether Content-Length and the length of the body
which has been transmitted are equal or not.</p>
<p>The request implements the <a href="stream.html#stream_class_stream_writable">Writable Stream</a> interface. This is an
<a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a> with the following events:</p>
<h3>Event: 'abort'<span><a class="mark" href="#http_event_abort" id="http_event_abort">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.4.1</span>
</div><p><code>function () { }</code></p>
<p>Emitted when the request has been aborted by the client. This event is only
emitted on the first call to <code>abort()</code>.</p>
<h3>Event: 'aborted'<span><a class="mark" href="#http_event_aborted" id="http_event_aborted">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.8</span>
</div><p><code>function () { }</code></p>
<p>Emitted when the request has been aborted by the server and the network
socket has closed.</p>
<h3>Event: 'connect'<span><a class="mark" href="#http_event_connect" id="http_event_connect">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p><code>function (response, socket, head) { }</code></p>
<p>Emitted each time a server responds to a request with a <code>CONNECT</code> method. If this
event isn't being listened for, clients receiving a <code>CONNECT</code> method will have
their connections closed.</p>
<p>A client and server pair that shows you how to listen for the <code>'connect'</code> event:</p>
<pre><code class="lang-js">const http = require('http');
const net = require('net');
const url = require('url');
// Create an HTTP tunneling proxy
var proxy = http.createServer( (req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('okay');
});
proxy.on('connect', (req, cltSocket, head) => {
// connect to an origin server
var srvUrl = url.parse(`http://${req.url}`);
var srvSocket = net.connect(srvUrl.port, srvUrl.hostname, () => {
cltSocket.write('HTTP/1.1 200 Connection Established\r\n' +
'Proxy-agent: Node.js-Proxy\r\n' +
'\r\n');
srvSocket.write(head);
srvSocket.pipe(cltSocket);
cltSocket.pipe(srvSocket);
});
});
// now that proxy is running
proxy.listen(1337, '127.0.0.1', () => {
// make a request to a tunneling proxy
var options = {
port: 1337,
hostname: '127.0.0.1',
method: 'CONNECT',
path: 'www.google.com:80'
};
var req = http.request(options);
req.end();
req.on('connect', (res, socket, head) => {
console.log('got connected!');
// make a request over an HTTP tunnel
socket.write('GET / HTTP/1.1\r\n' +
'Host: www.google.com:80\r\n' +
'Connection: close\r\n' +
'\r\n');
socket.on('data', (chunk) => {
console.log(chunk.toString());
});
socket.on('end', () => {
proxy.close();
});
});
});
</code></pre>
<h3>Event: 'continue'<span><a class="mark" href="#http_event_continue" id="http_event_continue">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.2</span>
</div><p><code>function () { }</code></p>
<p>Emitted when the server sends a '100 Continue' HTTP response, usually because
the request contained 'Expect: 100-continue'. This is an instruction that
the client should send the request body.</p>
<h3>Event: 'response'<span><a class="mark" href="#http_event_response" id="http_event_response">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.0</span>
</div><p><code>function (response) { }</code></p>
<p>Emitted when a response is received to this request. This event is emitted only
once. The <code>response</code> argument will be an instance of <a href="#http_class_http_incomingmessage"><code>http.IncomingMessage</code></a>.</p>
<h3>Event: 'socket'<span><a class="mark" href="#http_event_socket" id="http_event_socket">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.3</span>
</div><p><code>function (socket) { }</code></p>
<p>Emitted after a socket is assigned to this request.</p>
<h3>Event: 'upgrade'<span><a class="mark" href="#http_event_upgrade" id="http_event_upgrade">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p><code>function (response, socket, head) { }</code></p>
<p>Emitted each time a server responds to a request with an upgrade. If this
event isn't being listened for, clients receiving an upgrade header will have
their connections closed.</p>
<p>A client server pair that show you how to listen for the <code>'upgrade'</code> event.</p>
<pre><code class="lang-js">const http = require('http');
// Create an HTTP server
var srv = http.createServer( (req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('okay');
});
srv.on('upgrade', (req, socket, head) => {
socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' +
'Upgrade: WebSocket\r\n' +
'Connection: Upgrade\r\n' +
'\r\n');
socket.pipe(socket); // echo back
});
// now that server is running
srv.listen(1337, '127.0.0.1', () => {
// make a request
var options = {
port: 1337,
hostname: '127.0.0.1',
headers: {
'Connection': 'Upgrade',
'Upgrade': 'websocket'
}
};
var req = http.request(options);
req.end();
req.on('upgrade', (res, socket, upgradeHead) => {
console.log('got upgraded!');
socket.end();
process.exit(0);
});
});
</code></pre>
<h3>request.abort()<span><a class="mark" href="#http_request_abort" id="http_request_abort">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.8</span>
</div><p>Marks the request as aborting. Calling this will cause remaining data
in the response to be dropped and the socket to be destroyed.</p>
<h3>request.aborted<span><a class="mark" href="#http_request_aborted" id="http_request_aborted">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>If a request has been aborted, this value is the time when the request was
aborted, in milliseconds since 1 January 1970 00:00:00 UTC.</p>
<h3>request.end([data][, encoding][, callback])<span><a class="mark" href="#http_request_end_data_encoding_callback" id="http_request_end_data_encoding_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Finishes sending the request. If any parts of the body are
unsent, it will flush them to the stream. If the request is
chunked, this will send the terminating <code>'0\r\n\r\n'</code>.</p>
<p>If <code>data</code> is specified, it is equivalent to calling
<a href="#http_response_write_chunk_encoding_callback"><code>response.write(data, encoding)</code></a> followed by <code>request.end(callback)</code>.</p>
<p>If <code>callback</code> is specified, it will be called when the request stream
is finished.</p>
<h3>request.flushHeaders()<span><a class="mark" href="#http_request_flushheaders" id="http_request_flushheaders">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v1.6.0</span>
</div><p>Flush the request headers.</p>
<p>For efficiency reasons, Node.js normally buffers the request headers until you
call <code>request.end()</code> or write the first chunk of request data. It then tries
hard to pack the request headers and data into a single TCP packet.</p>
<p>That's usually what you want (it saves a TCP round-trip) but not when the first
data isn't sent until possibly much later. <code>request.flushHeaders()</code> lets you bypass
the optimization and kickstart the request.</p>
<h3>request.setNoDelay([noDelay])<span><a class="mark" href="#http_request_setnodelay_nodelay" id="http_request_setnodelay_nodelay">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><p>Once a socket is assigned to this request and is connected
<a href="net.html#net_socket_setnodelay_nodelay"><code>socket.setNoDelay()</code></a> will be called.</p>
<h3>request.setSocketKeepAlive([enable][, initialDelay])<span><a class="mark" href="#http_request_setsocketkeepalive_enable_initialdelay" id="http_request_setsocketkeepalive_enable_initialdelay">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><p>Once a socket is assigned to this request and is connected
<a href="net.html#net_socket_setkeepalive_enable_initialdelay"><code>socket.setKeepAlive()</code></a> will be called.</p>
<h3>request.setTimeout(timeout[, callback])<span><a class="mark" href="#http_request_settimeout_timeout_callback" id="http_request_settimeout_timeout_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><p>Once a socket is assigned to this request and is connected
<a href="#net_socket_settimeout_timeout_callback"><code>socket.setTimeout()</code></a> will be called.</p>
<ul>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Milliseconds before a request is considered to be timed out.</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Optional function to be called when a timeout occurs. Same as binding to the <code>timeout</code> event.</li>
</ul>
<p>Returns <code>request</code>.</p>
<h3>request.write(chunk[, encoding][, callback])<span><a class="mark" href="#http_request_write_chunk_encoding_callback" id="http_request_write_chunk_encoding_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.29</span>
</div><p>Sends a chunk of the body. By calling this method
many times, the user can stream a request body to a
server--in that case it is suggested to use the
<code>['Transfer-Encoding', 'chunked']</code> header line when
creating the request.</p>
<p>The <code>chunk</code> argument should be a <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> or a string.</p>
<p>The <code>encoding</code> argument is optional and only applies when <code>chunk</code> is a string.
Defaults to <code>'utf8'</code>.</p>
<p>The <code>callback</code> argument is optional and will be called when this chunk of data
is flushed.</p>
<p>Returns <code>request</code>.</p>
<h2>Class: http.Server<span><a class="mark" href="#http_class_http_server" id="http_class_http_server">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.17</span>
</div><p>This class inherits from <a href="net.html#net_class_net_server"><code>net.Server</code></a> and has the following additional events:</p>
<h3>Event: 'checkContinue'<span><a class="mark" href="#http_event_checkcontinue" id="http_event_checkcontinue">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p><code>function (request, response) { }</code></p>
<p>Emitted each time a request with an http Expect: 100-continue is received.
If this event isn't listened for, the server will automatically respond
with a 100 Continue as appropriate.</p>
<p>Handling this event involves calling <a href="#http_response_writecontinue"><code>response.writeContinue()</code></a> if the client
should continue to send the request body, or generating an appropriate HTTP
response (e.g. 400 Bad Request) if the client should not continue to send the
request body.</p>
<p>Note that when this event is emitted and handled, the <code>'request'</code> event will
not be emitted.</p>
<h3>Event: 'clientError'<span><a class="mark" href="#http_event_clienterror" id="http_event_clienterror">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p><code>function (exception, socket) { }</code></p>
<p>If a client connection emits an <code>'error'</code> event, it will be forwarded here.</p>
<p><code>socket</code> is the <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> object that the error originated from.</p>
<h3>Event: 'close'<span><a class="mark" href="#http_event_close" id="http_event_close">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.4</span>
</div><p><code>function () { }</code></p>
<p>Emitted when the server closes.</p>
<h3>Event: 'connect'<span><a class="mark" href="#http_event_connect_1" id="http_event_connect_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p><code>function (request, socket, head) { }</code></p>
<p>Emitted each time a client requests a http <code>CONNECT</code> method. If this event isn't
listened for, then clients requesting a <code>CONNECT</code> method will have their
connections closed.</p>
<ul>
<li><code>request</code> is the arguments for the http request, as it is in the request
event.</li>
<li><code>socket</code> is the network socket between the server and client.</li>
<li><code>head</code> is an instance of Buffer, the first packet of the tunneling stream,
this may be empty.</li>
</ul>
<p>After this event is emitted, the request's socket will not have a <code>'data'</code>
event listener, meaning you will need to bind to it in order to handle data
sent to the server on that socket.</p>
<h3>Event: 'connection'<span><a class="mark" href="#http_event_connection" id="http_event_connection">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.0</span>
</div><p><code>function (socket) { }</code></p>
<p>When a new TCP stream is established. <code>socket</code> is an object of type
<a href="net.html#net_class_net_socket"><code>net.Socket</code></a>. Usually users will not want to access this event. In
particular, the socket will not emit <code>'readable'</code> events because of how
the protocol parser attaches to the socket. The <code>socket</code> can also be
accessed at <code>request.connection</code>.</p>
<h3>Event: 'request'<span><a class="mark" href="#http_event_request" id="http_event_request">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.0</span>
</div><p><code>function (request, response) { }</code></p>
<p>Emitted each time there is a request. Note that there may be multiple requests
per connection (in the case of keep-alive connections).
<code>request</code> is an instance of <a href="#http_class_http_incomingmessage"><code>http.IncomingMessage</code></a> and <code>response</code> is
an instance of <a href="#http_class_http_serverresponse"><code>http.ServerResponse</code></a>.</p>
<h3>Event: 'upgrade'<span><a class="mark" href="#http_event_upgrade_1" id="http_event_upgrade_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.94</span>
</div><p><code>function (request, socket, head) { }</code></p>
<p>Emitted each time a client requests a http upgrade. If this event isn't
listened for, then clients requesting an upgrade will have their connections
closed.</p>
<ul>
<li><code>request</code> is the arguments for the http request, as it is in the request
event.</li>
<li><code>socket</code> is the network socket between the server and client.</li>
<li><code>head</code> is an instance of Buffer, the first packet of the upgraded stream,
this may be empty.</li>
</ul>
<p>After this event is emitted, the request's socket will not have a <code>'data'</code>
event listener, meaning you will need to bind to it in order to handle data
sent to the server on that socket.</p>
<h3>server.close([callback])<span><a class="mark" href="#http_server_close_callback" id="http_server_close_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Stops the server from accepting new connections. See <a href="net.html#net_server_close_callback"><code>net.Server.close()</code></a>.</p>
<h3>server.listen(handle[, callback])<span><a class="mark" href="#http_server_listen_handle_callback" id="http_server_listen_handle_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.10</span>
</div><ul>
<li><code>handle</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>The <code>handle</code> object can be set to either a server or socket (anything
with an underlying <code>_handle</code> member), or a <code>{fd: <n>}</code> object.</p>
<p>This will cause the server to accept connections on the specified
handle, but it is presumed that the file descriptor or handle has
already been bound to a port or domain socket.</p>
<p>Listening on a file descriptor is not supported on Windows.</p>
<p>This function is asynchronous. <code>callback</code> will be added as a listener for the
<code>'listening'</code> event. See also <a href="net.html#net_server_listen_handle_callback"><code>net.Server.listen()</code></a>.</p>
<p>Returns <code>server</code>.</p>
<h3>server.listen(path[, callback])<span><a class="mark" href="#http_server_listen_path_callback" id="http_server_listen_path_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Start a UNIX socket server listening for connections on the given <code>path</code>.</p>
<p>This function is asynchronous. <code>callback</code> will be added as a listener for the
<code>'listening'</code> event. See also <a href="net.html#net_server_listen_path_callback"><code>net.Server.listen(path)</code></a>.</p>
<h3>server.listen([port][, hostname][, backlog][, callback])<span><a class="mark" href="#http_server_listen_port_hostname_backlog_callback" id="http_server_listen_port_hostname_backlog_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Begin accepting connections on the specified <code>port</code> and <code>hostname</code>. If the
<code>hostname</code> is omitted, the server will accept connections on any IPv6 address
(<code>::</code>) when IPv6 is available, or any IPv4 address (<code>0.0.0.0</code>) otherwise.
Omit the port argument, or use a port value of <code>0</code>, to have the operating system
assign a random port, which can be retrieved by using <code>server.address().port</code>
after the <code>'listening'</code> event has been emitted.</p>
<p>To listen to a unix socket, supply a filename instead of port and hostname.</p>
<p>Backlog is the maximum length of the queue of pending connections.
The actual length will be determined by your OS through sysctl settings such as
<code>tcp_max_syn_backlog</code> and <code>somaxconn</code> on linux. The default value of this
parameter is 511 (not 512).</p>
<p>This function is asynchronous. <code>callback</code> will be added as a listener for the
<code>'listening'</code> event. See also <a href="net.html#net_server_listen_port_hostname_backlog_callback"><code>net.Server.listen(port)</code></a>.</p>
<h3>server.maxHeadersCount<span><a class="mark" href="#http_server_maxheaderscount" id="http_server_maxheaderscount">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p>Limits maximum incoming headers count, equal to 1000 by default. If set to 0 -
no limit will be applied.</p>
<h3>server.setTimeout(msecs, callback)<span><a class="mark" href="#http_server_settimeout_msecs_callback" id="http_server_settimeout_msecs_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.12</span>
</div><ul>
<li><code>msecs</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Sets the timeout value for sockets, and emits a <code>'timeout'</code> event on
the Server object, passing the socket as an argument, if a timeout
occurs.</p>
<p>If there is a <code>'timeout'</code> event listener on the Server object, then it
will be called with the timed-out socket as an argument.</p>
<p>By default, the Server's timeout value is 2 minutes, and sockets are
destroyed automatically if they time out. However, if you assign a
callback to the Server's <code>'timeout'</code> event, then you are responsible
for handling socket timeouts.</p>
<p>Returns <code>server</code>.</p>
<h3>server.timeout<span><a class="mark" href="#http_server_timeout" id="http_server_timeout">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.12</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Default = 120000 (2 minutes)</li>
</ul>
<p>The number of milliseconds of inactivity before a socket is presumed
to have timed out.</p>
<p>Note that the socket timeout logic is set up on connection, so
changing this value only affects <em>new</em> connections to the server, not
any existing connections.</p>
<p>Set to 0 to disable any kind of automatic timeout behavior on incoming
connections.</p>
<h2>Class: http.ServerResponse<span><a class="mark" href="#http_class_http_serverresponse" id="http_class_http_serverresponse">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.17</span>
</div><p>This object is created internally by a HTTP server--not by the user. It is
passed as the second parameter to the <code>'request'</code> event.</p>
<p>The response implements, but does not inherit from, the <a href="stream.html#stream_class_stream_writable">Writable Stream</a>
interface. This is an <a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a> with the following events:</p>
<h3>Event: 'close'<span><a class="mark" href="#http_event_close_1" id="http_event_close_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.7</span>
</div><p><code>function () { }</code></p>
<p>Indicates that the underlying connection was terminated before
<a href="#http_response_end_data_encoding_callback"><code>response.end()</code></a> was called or able to flush.</p>
<h3>Event: 'finish'<span><a class="mark" href="#http_event_finish" id="http_event_finish">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.6</span>
</div><p><code>function () { }</code></p>
<p>Emitted when the response has been sent. More specifically, this event is
emitted when the last segment of the response headers and body have been
handed off to the operating system for transmission over the network. It
does not imply that the client has received anything yet.</p>
<p>After this event, no more events will be emitted on the response object.</p>
<h3>response.addTrailers(headers)<span><a class="mark" href="#http_response_addtrailers_headers" id="http_response_addtrailers_headers">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>This method adds HTTP trailing headers (a header but at the end of the
message) to the response.</p>
<p>Trailers will <strong>only</strong> be emitted if chunked encoding is used for the
response; if it is not (e.g. if the request was HTTP/1.0), they will
be silently discarded.</p>
<p>Note that HTTP requires the <code>Trailer</code> header to be sent if you intend to
emit trailers, with a list of the header fields in its value. E.g.,</p>
<pre><code class="lang-js">response.writeHead(200, { 'Content-Type': 'text/plain',
'Trailer': 'Content-MD5' });
response.write(fileData);
response.addTrailers({'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667'});
response.end();
</code></pre>
<p>Attempting to set a header field name or value that contains invalid characters
will result in a <a href="errors.html#errors_class_typeerror"><code>TypeError</code></a> being thrown.</p>
<h3>response.end([data][, encoding][, callback])<span><a class="mark" href="#http_response_end_data_encoding_callback" id="http_response_end_data_encoding_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>This method signals to the server that all of the response headers and body
have been sent; that server should consider this message complete.
The method, <code>response.end()</code>, MUST be called on each response.</p>
<p>If <code>data</code> is specified, it is equivalent to calling
<a href="#http_response_write_chunk_encoding_callback"><code>response.write(data, encoding)</code></a> followed by <code>response.end(callback)</code>.</p>
<p>If <code>callback</code> is specified, it will be called when the response stream
is finished.</p>
<h3>response.finished<span><a class="mark" href="#http_response_finished" id="http_response_finished">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.0.2</span>
</div><p>Boolean value that indicates whether the response has completed. Starts
as <code>false</code>. After <a href="#http_response_end_data_encoding_callback"><code>response.end()</code></a> executes, the value will be <code>true</code>.</p>
<h3>response.getHeader(name)<span><a class="mark" href="#http_response_getheader_name" id="http_response_getheader_name">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.4.0</span>
</div><p>Reads out a header that's already been queued but not sent to the client. Note
that the name is case insensitive. This can only be called before headers get
implicitly flushed.</p>
<p>Example:</p>
<pre><code class="lang-js">var contentType = response.getHeader('content-type');
</code></pre>
<h3>response.headersSent<span><a class="mark" href="#http_response_headerssent" id="http_response_headerssent">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.3</span>
</div><p>Boolean (read-only). True if headers were sent, false otherwise.</p>
<h3>response.removeHeader(name)<span><a class="mark" href="#http_response_removeheader_name" id="http_response_removeheader_name">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.4.0</span>
</div><p>Removes a header that's queued for implicit sending.</p>
<p>Example:</p>
<pre><code class="lang-js">response.removeHeader('Content-Encoding');
</code></pre>
<h3>response.sendDate<span><a class="mark" href="#http_response_senddate" id="http_response_senddate">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.5</span>
</div><p>When true, the Date header will be automatically generated and sent in
the response if it is not already present in the headers. Defaults to true.</p>
<p>This should only be disabled for testing; HTTP requires the Date header
in responses.</p>
<h3>response.setHeader(name, value)<span><a class="mark" href="#http_response_setheader_name_value" id="http_response_setheader_name_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.4.0</span>
</div><p>Sets a single header value for implicit headers. If this header already exists
in the to-be-sent headers, its value will be replaced. Use an array of strings
here if you need to send multiple headers with the same name.</p>
<p>Example:</p>
<pre><code class="lang-js">response.setHeader('Content-Type', 'text/html');
</code></pre>
<p>or</p>
<pre><code class="lang-js">response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']);
</code></pre>
<p>Attempting to set a header field name or value that contains invalid characters
will result in a <a href="errors.html#errors_class_typeerror"><code>TypeError</code></a> being thrown.</p>
<p>When headers have been set with <a href="#http_response_setheader_name_value"><code>response.setHeader()</code></a>, they will be merged with
any headers passed to <a href="#http_response_writehead_statuscode_statusmessage_headers"><code>response.writeHead()</code></a>, with the headers passed to
<a href="#http_response_writehead_statuscode_statusmessage_headers"><code>response.writeHead()</code></a> given precedence.</p>
<pre><code class="lang-js">// returns content-type = text/plain
const server = http.createServer((req,res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('ok');
});
</code></pre>
<h3>response.setTimeout(msecs, callback)<span><a class="mark" href="#http_response_settimeout_msecs_callback" id="http_response_settimeout_msecs_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.12</span>
</div><ul>
<li><code>msecs</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Sets the Socket's timeout value to <code>msecs</code>. If a callback is
provided, then it is added as a listener on the <code>'timeout'</code> event on
the response object.</p>
<p>If no <code>'timeout'</code> listener is added to the request, the response, or
the server, then sockets are destroyed when they time out. If you
assign a handler on the request, the response, or the server's
<code>'timeout'</code> events, then it is your responsibility to handle timed out
sockets.</p>
<p>Returns <code>response</code>.</p>
<h3>response.statusCode<span><a class="mark" href="#http_response_statuscode" id="http_response_statuscode">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.4.0</span>
</div><p>When using implicit headers (not calling <a href="#http_response_writehead_statuscode_statusmessage_headers"><code>response.writeHead()</code></a> explicitly),
this property controls the status code that will be sent to the client when
the headers get flushed.</p>
<p>Example:</p>
<pre><code class="lang-js">response.statusCode = 404;
</code></pre>
<p>After response header was sent to the client, this property indicates the
status code which was sent out.</p>
<h3>response.statusMessage<span><a class="mark" href="#http_response_statusmessage" id="http_response_statusmessage">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.8</span>
</div><p>When using implicit headers (not calling <a href="#http_response_writehead_statuscode_statusmessage_headers"><code>response.writeHead()</code></a> explicitly), this property
controls the status message that will be sent to the client when the headers get
flushed. If this is left as <code>undefined</code> then the standard message for the status
code will be used.</p>
<p>Example:</p>
<pre><code class="lang-js">response.statusMessage = 'Not found';
</code></pre>
<p>After response header was sent to the client, this property indicates the
status message which was sent out.</p>
<h3>response.write(chunk[, encoding][, callback])<span><a class="mark" href="#http_response_write_chunk_encoding_callback" id="http_response_write_chunk_encoding_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.29</span>
</div><p>If this method is called and <a href="#http_response_writehead_statuscode_statusmessage_headers"><code>response.writeHead()</code></a> has not been called,
it will switch to implicit header mode and flush the implicit headers.</p>
<p>This sends a chunk of the response body. This method may
be called multiple times to provide successive parts of the body.</p>
<p><code>chunk</code> can be a string or a buffer. If <code>chunk</code> is a string,
the second parameter specifies how to encode it into a byte stream.
By default the <code>encoding</code> is <code>'utf8'</code>. <code>callback</code> will be called when this chunk
of data is flushed.</p>
<p><strong>Note</strong>: This is the raw HTTP body and has nothing to do with
higher-level multi-part body encodings that may be used.</p>
<p>The first time <a href="#http_response_write_chunk_encoding_callback"><code>response.write()</code></a> is called, it will send the buffered
header information and the first body to the client. The second time
<a href="#http_response_write_chunk_encoding_callback"><code>response.write()</code></a> is called, Node.js assumes you're going to be streaming
data, and sends that separately. That is, the response is buffered up to the
first chunk of body.</p>
<p>Returns <code>true</code> if the entire data was flushed successfully to the kernel
buffer. Returns <code>false</code> if all or part of the data was queued in user memory.
<code>'drain'</code> will be emitted when the buffer is free again.</p>
<h3>response.writeContinue()<span><a class="mark" href="#http_response_writecontinue" id="http_response_writecontinue">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>Sends a HTTP/1.1 100 Continue message to the client, indicating that
the request body should be sent. See the <a href="#http_event_checkcontinue"><code>'checkContinue'</code></a> event on <code>Server</code>.</p>
<h3>response.writeHead(statusCode[, statusMessage][, headers])<span><a class="mark" href="#http_response_writehead_statuscode_statusmessage_headers" id="http_response_writehead_statuscode_statusmessage_headers">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.30</span>
</div><p>Sends a response header to the request. The status code is a 3-digit HTTP
status code, like <code>404</code>. The last argument, <code>headers</code>, are the response headers.
Optionally one can give a human-readable <code>statusMessage</code> as the second
argument.</p>
<p>Example:</p>
<pre><code class="lang-js">var body = 'hello world';
response.writeHead(200, {
'Content-Length': Buffer.byteLength(body),
'Content-Type': 'text/plain' });
</code></pre>
<p>This method must only be called once on a message and it must
be called before <a href="#http_response_end_data_encoding_callback"><code>response.end()</code></a> is called.</p>
<p>If you call <a href="#http_response_write_chunk_encoding_callback"><code>response.write()</code></a> or <a href="#http_response_end_data_encoding_callback"><code>response.end()</code></a> before calling this,
the implicit/mutable headers will be calculated and call this function for you.</p>
<p>When headers have been set with <a href="#http_response_setheader_name_value"><code>response.setHeader()</code></a>, they will be merged with
any headers passed to <a href="#http_response_writehead_statuscode_statusmessage_headers"><code>response.writeHead()</code></a>, with the headers passed to
<a href="#http_response_writehead_statuscode_statusmessage_headers"><code>response.writeHead()</code></a> given precedence.</p>
<pre><code class="lang-js">// returns content-type = text/plain
const server = http.createServer((req,res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('ok');
});
</code></pre>
<p>Note that Content-Length is given in bytes not characters. The above example
works because the string <code>'hello world'</code> contains only single byte characters.
If the body contains higher coded characters then <code>Buffer.byteLength()</code>
should be used to determine the number of bytes in a given encoding.
And Node.js does not check whether Content-Length and the length of the body
which has been transmitted are equal or not.</p>
<p>Attempting to set a header field name or value that contains invalid characters
will result in a <a href="errors.html#errors_class_typeerror"><code>TypeError</code></a> being thrown.</p>
<h2>Class: http.IncomingMessage<span><a class="mark" href="#http_class_http_incomingmessage" id="http_class_http_incomingmessage">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.17</span>
</div><p>An <code>IncomingMessage</code> object is created by <a href="http.html#http_class_http_server"><code>http.Server</code></a> or
<a href="#http_class_http_clientrequest"><code>http.ClientRequest</code></a> and passed as the first argument to the <code>'request'</code>
and <code>'response'</code> event respectively. It may be used to access response status,
headers and data.</p>
<p>It implements the <a href="stream.html#stream_class_stream_readable">Readable Stream</a> interface, as well as the
following additional events, methods, and properties.</p>
<h3>Event: 'aborted'<span><a class="mark" href="#http_event_aborted_1" id="http_event_aborted_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.8</span>
</div><p><code>function () { }</code></p>
<p>Emitted when the request has been aborted by the client and the network
socket has closed.</p>
<h3>Event: 'close'<span><a class="mark" href="#http_event_close_2" id="http_event_close_2">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.4.2</span>
</div><p><code>function () { }</code></p>
<p>Indicates that the underlying connection was closed.
Just like <code>'end'</code>, this event occurs only once per response.</p>
<h3>message.destroy([error])<span><a class="mark" href="#http_message_destroy_error" id="http_message_destroy_error">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><ul>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Calls <code>destroy()</code> on the socket that received the <code>IncomingMessage</code>. If <code>error</code>
is provided, an <code>'error'</code> event is emitted and <code>error</code> is passed as an argument
to any listeners on the event.</p>
<h3>message.headers<span><a class="mark" href="#http_message_headers" id="http_message_headers">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.5</span>
</div><p>The request/response headers object.</p>
<p>Key-value pairs of header names and values. Header names are lower-cased.
Example:</p>
<pre><code class="lang-js">// Prints something like:
//
// { 'user-agent': 'curl/7.22.0',
// host: '127.0.0.1:8000',
// accept: '*/*' }
console.log(request.headers);
</code></pre>
<p>Duplicates in raw headers are handled in the following ways, depending on the
header name:</p>
<ul>
<li>Duplicates of <code>age</code>, <code>authorization</code>, <code>content-length</code>, <code>content-type</code>,
<code>etag</code>, <code>expires</code>, <code>from</code>, <code>host</code>, <code>if-modified-since</code>, <code>if-unmodified-since</code>,
<code>last-modified</code>, <code>location</code>, <code>max-forwards</code>, <code>proxy-authorization</code>, <code>referer</code>,
<code>retry-after</code>, or <code>user-agent</code> are discarded.</li>
<li><code>set-cookie</code> is always an array. Duplicates are added to the array.</li>
<li>For all other headers, the values are joined together with ', '.</li>
</ul>
<h3>message.httpVersion<span><a class="mark" href="#http_message_httpversion" id="http_message_httpversion">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.1</span>
</div><p>In case of server request, the HTTP version sent by the client. In the case of
client response, the HTTP version of the connected-to server.
Probably either <code>'1.1'</code> or <code>'1.0'</code>.</p>
<p>Also <code>message.httpVersionMajor</code> is the first integer and
<code>message.httpVersionMinor</code> is the second.</p>
<h3>message.method<span><a class="mark" href="#http_message_method" id="http_message_method">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.1</span>
</div><p><strong>Only valid for request obtained from <a href="http.html#http_class_http_server"><code>http.Server</code></a>.</strong></p>
<p>The request method as a string. Read only. Example:
<code>'GET'</code>, <code>'DELETE'</code>.</p>
<h3>message.rawHeaders<span><a class="mark" href="#http_message_rawheaders" id="http_message_rawheaders">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.6</span>
</div><p>The raw request/response headers list exactly as they were received.</p>
<p>Note that the keys and values are in the same list. It is <em>not</em> a
list of tuples. So, the even-numbered offsets are key values, and the
odd-numbered offsets are the associated values.</p>
<p>Header names are not lowercased, and duplicates are not merged.</p>
<pre><code class="lang-js">// Prints something like:
//
// [ 'user-agent',
// 'this is invalid because there can be only one',
// 'User-Agent',
// 'curl/7.22.0',
// 'Host',
// '127.0.0.1:8000',
// 'ACCEPT',
// '*/*' ]
console.log(request.rawHeaders);
</code></pre>
<h3>message.rawTrailers<span><a class="mark" href="#http_message_rawtrailers" id="http_message_rawtrailers">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.6</span>
</div><p>The raw request/response trailer keys and values exactly as they were
received. Only populated at the <code>'end'</code> event.</p>
<h3>message.setTimeout(msecs, callback)<span><a class="mark" href="#http_message_settimeout_msecs_callback" id="http_message_settimeout_msecs_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><ul>
<li><code>msecs</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Calls <code>message.connection.setTimeout(msecs, callback)</code>.</p>
<p>Returns <code>message</code>.</p>
<h3>message.statusCode<span><a class="mark" href="#http_message_statuscode" id="http_message_statuscode">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.1</span>
</div><p><strong>Only valid for response obtained from <a href="#http_class_http_clientrequest"><code>http.ClientRequest</code></a>.</strong></p>
<p>The 3-digit HTTP response status code. E.G. <code>404</code>.</p>
<h3>message.statusMessage<span><a class="mark" href="#http_message_statusmessage" id="http_message_statusmessage">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.10</span>
</div><p><strong>Only valid for response obtained from <a href="#http_class_http_clientrequest"><code>http.ClientRequest</code></a>.</strong></p>
<p>The HTTP response status message (reason phrase). E.G. <code>OK</code> or <code>Internal Server Error</code>.</p>
<h3>message.socket<span><a class="mark" href="#http_message_socket" id="http_message_socket">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>The <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> object associated with the connection.</p>
<p>With HTTPS support, use <a href="tls.html#tls_tlssocket_getpeercertificate_detailed"><code>request.socket.getPeerCertificate()</code></a> to obtain the
client's authentication details.</p>
<h3>message.trailers<span><a class="mark" href="#http_message_trailers" id="http_message_trailers">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>The request/response trailers object. Only populated at the <code>'end'</code> event.</p>
<h3>message.url<span><a class="mark" href="#http_message_url" id="http_message_url">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p><strong>Only valid for request obtained from <a href="http.html#http_class_http_server"><code>http.Server</code></a>.</strong></p>
<p>Request URL string. This contains only the URL that is
present in the actual HTTP request. If the request is:</p>
<pre><code>GET /status?name=ryan HTTP/1.1\r\n
Accept: text/plain\r\n
\r\n
</code></pre><p>Then <code>request.url</code> will be:</p>
<pre><code>'/status?name=ryan'
</code></pre><p>If you would like to parse the URL into its parts, you can use
<code>require('url').parse(request.url)</code>. Example:</p>
<pre><code>$ node
> require('url').parse('/status?name=ryan')
{
href: '/status?name=ryan',
search: '?name=ryan',
query: 'name=ryan',
pathname: '/status'
}
</code></pre><p>If you would like to extract the parameters from the query string,
you can use the <code>require('querystring').parse</code> function, or pass
<code>true</code> as the second argument to <code>require('url').parse</code>. Example:</p>
<pre><code>$ node
> require('url').parse('/status?name=ryan', true)
{
href: '/status?name=ryan',
search: '?name=ryan',
query: {name: 'ryan'},
pathname: '/status'
}
</code></pre><h2>http.METHODS<span><a class="mark" href="#http_http_methods" id="http_http_methods">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.8</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a></li>
</ul>
<p>A list of the HTTP methods that are supported by the parser.</p>
<h2>http.STATUS_CODES<span><a class="mark" href="#http_http_status_codes" id="http_http_status_codes">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.22</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>A collection of all the standard HTTP response status codes, and the
short description of each. For example, <code>http.STATUS_CODES[404] === 'Not
Found'</code>.</p>
<h2>http.createClient([port][, host])<span><a class="mark" href="#http_http_createclient_port_host" id="http_http_createclient_port_host">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.13</span>
<span>Deprecated since: v0.3.6 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="http.html#http_http_request_options_callback"><code>http.request()</code></a> instead.</pre><p>Constructs a new HTTP client. <code>port</code> and <code>host</code> refer to the server to be
connected to.</p>
<h2>http.createServer([requestListener])<span><a class="mark" href="#http_http_createserver_requestlistener" id="http_http_createserver_requestlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.13</span>
</div><p>Returns a new instance of <a href="http.html#http_class_http_server"><code>http.Server</code></a>.</p>
<p>The <code>requestListener</code> is a function which is automatically
added to the <code>'request'</code> event.</p>
<h2>http.get(options[, callback])<span><a class="mark" href="#http_http_get_options_callback" id="http_http_get_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.6</span>
</div><p>Since most requests are GET requests without bodies, Node.js provides this
convenience method. The only difference between this method and <a href="http.html#http_http_request_options_callback"><code>http.request()</code></a>
is that it sets the method to GET and calls <code>req.end()</code> automatically.</p>
<p>Example:</p>
<pre><code class="lang-js">http.get('http://www.google.com/index.html', (res) => {
console.log(`Got response: ${res.statusCode}`);
// consume response body
res.resume();
}).on('error', (e) => {
console.log(`Got error: ${e.message}`);
});
</code></pre>
<h2>http.globalAgent<span><a class="mark" href="#http_http_globalagent" id="http_http_globalagent">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><p>Global instance of Agent which is used as the default for all http client
requests.</p>
<h2>http.request(options[, callback])<span><a class="mark" href="#http_http_request_options_callback" id="http_http_request_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.6</span>
</div><p>Node.js maintains several connections per server to make HTTP requests.
This function allows one to transparently issue requests.</p>
<p><code>options</code> can be an object or a string. If <code>options</code> is a string, it is
automatically parsed with <a href="url.html#url_url_parse_urlstr_parsequerystring_slashesdenotehost"><code>url.parse()</code></a>.</p>
<p>Options:</p>
<ul>
<li><code>protocol</code>: Protocol to use. Defaults to <code>'http:'</code>.</li>
<li><code>host</code>: A domain name or IP address of the server to issue the request to.
Defaults to <code>'localhost'</code>.</li>
<li><code>hostname</code>: Alias for <code>host</code>. To support <a href="url.html#url_url_parse_urlstr_parsequerystring_slashesdenotehost"><code>url.parse()</code></a> <code>hostname</code> is
preferred over <code>host</code>.</li>
<li><code>family</code>: IP address family to use when resolving <code>host</code> and <code>hostname</code>.
Valid values are <code>4</code> or <code>6</code>. When unspecified, both IP v4 and v6 will be
used.</li>
<li><code>port</code>: Port of remote server. Defaults to 80.</li>
<li><code>localAddress</code>: Local interface to bind for network connections.</li>
<li><code>socketPath</code>: Unix Domain Socket (use one of host:port or socketPath).</li>
<li><code>method</code>: A string specifying the HTTP request method. Defaults to <code>'GET'</code>.</li>
<li><code>path</code>: Request path. Defaults to <code>'/'</code>. Should include query string if any.
E.G. <code>'/index.html?page=12'</code>. An exception is thrown when the request path
contains illegal characters. Currently, only spaces are rejected but that
may change in the future.</li>
<li><code>headers</code>: An object containing request headers.</li>
<li><code>auth</code>: Basic authentication i.e. <code>'user:password'</code> to compute an
Authorization header.</li>
<li><code>agent</code>: Controls <a href="#https_class_https_agent"><code>Agent</code></a> behavior. When an Agent is used request will
default to <code>Connection: keep-alive</code>. Possible values:<ul>
<li><code>undefined</code> (default): use <a href="#http_http_globalagent"><code>http.globalAgent</code></a> for this host and port.</li>
<li><code>Agent</code> object: explicitly use the passed in <code>Agent</code>.</li>
<li><code>false</code>: opts out of connection pooling with an Agent, defaults request to
<code>Connection: close</code>.</li>
</ul>
</li>
</ul>
<p>The optional <code>callback</code> parameter will be added as a one time listener for
the <code>'response'</code> event.</p>
<p><code>http.request()</code> returns an instance of the <a href="#http_class_http_clientrequest"><code>http.ClientRequest</code></a>
class. The <code>ClientRequest</code> instance is a writable stream. If one needs to
upload a file with a POST request, then write to the <code>ClientRequest</code> object.</p>
<p>Example:</p>
<pre><code class="lang-js">var postData = querystring.stringify({
'msg' : 'Hello World!'
});
var options = {
hostname: 'www.google.com',
port: 80,
path: '/upload',
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-urlencoded',
'Content-Length': Buffer.byteLength(postData)
}
};
var req = http.request(options, (res) => {
console.log(`STATUS: ${res.statusCode}`);
console.log(`HEADERS: ${JSON.stringify(res.headers)}`);
res.setEncoding('utf8');
res.on('data', (chunk) => {
console.log(`BODY: ${chunk}`);
});
res.on('end', () => {
console.log('No more data in response.')
})
});
req.on('error', (e) => {
console.log(`problem with request: ${e.message}`);
});
// write data to request body
req.write(postData);
req.end();
</code></pre>
<p>Note that in the example <code>req.end()</code> was called. With <code>http.request()</code> one
must always call <code>req.end()</code> to signify that you're done with the request -
even if there is no data being written to the request body.</p>
<p>If any error is encountered during the request (be that with DNS resolution,
TCP level errors, or actual HTTP parse errors) an <code>'error'</code> event is emitted
on the returned request object. As with all <code>'error'</code> events, if no listeners
are registered the error will be thrown.</p>
<p>There are a few special headers that should be noted.</p>
<ul>
<li><p>Sending a 'Connection: keep-alive' will notify Node.js that the connection to
the server should be persisted until the next request.</p>
</li>
<li><p>Sending a 'Content-Length' header will disable the default chunked encoding.</p>
</li>
<li><p>Sending an 'Expect' header will immediately send the request headers.
Usually, when sending 'Expect: 100-continue', you should both set a timeout
and listen for the <code>'continue'</code> event. See RFC2616 Section 8.2.3 for more
information.</p>
</li>
<li><p>Sending an Authorization header will override using the <code>auth</code> option
to compute basic authentication.</p>
</li>
</ul>
<!-- [end-include:http.md] -->
<!-- [start-include:https.md] -->
<h1>HTTPS<span><a class="mark" href="#https_https" id="https_https">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>HTTPS is the HTTP protocol over TLS/SSL. In Node.js this is implemented as a
separate module.</p>
<h2>Class: https.Agent<span><a class="mark" href="#https_class_https_agent" id="https_class_https_agent">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.4.5</span>
</div><p>An Agent object for HTTPS similar to <a href="http.html#http_class_http_agent"><code>http.Agent</code></a>. See <a href="#https_https_request_options_callback"><code>https.request()</code></a>
for more information.</p>
<h2>Class: https.Server<span><a class="mark" href="#https_class_https_server" id="https_class_https_server">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><p>This class is a subclass of <code>tls.Server</code> and emits events same as
<a href="http.html#http_class_http_server"><code>http.Server</code></a>. See <a href="http.html#http_class_http_server"><code>http.Server</code></a> for more information.</p>
<h3>server.setTimeout(msecs, callback)<span><a class="mark" href="#https_server_settimeout_msecs_callback" id="https_server_settimeout_msecs_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.2</span>
</div><p>See <a href="http.html#http_server_settimeout_msecs_callback"><code>http.Server#setTimeout()</code></a>.</p>
<h3>server.timeout<span><a class="mark" href="#https_server_timeout" id="https_server_timeout">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.2</span>
</div><p>See <a href="http.html#http_server_timeout"><code>http.Server#timeout</code></a>.</p>
<h2>https.createServer(options[, requestListener])<span><a class="mark" href="#https_https_createserver_options_requestlistener" id="https_https_createserver_options_requestlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><p>Returns a new HTTPS web server object. The <code>options</code> is similar to
<a href="#tls_tls_createserver_options_secureconnectionlistener"><code>tls.createServer()</code></a>. The <code>requestListener</code> is a function which is
automatically added to the <code>'request'</code> event.</p>
<p>Example:</p>
<pre><code class="lang-js">// curl -k https://localhost:8000/
const https = require('https');
const fs = require('fs');
const options = {
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
https.createServer(options, (req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
</code></pre>
<p>Or</p>
<pre><code class="lang-js">const https = require('https');
const fs = require('fs');
const options = {
pfx: fs.readFileSync('server.pfx')
};
https.createServer(options, (req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
</code></pre>
<h3>server.close([callback])<span><a class="mark" href="#https_server_close_callback" id="https_server_close_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>See <a href="http.html#http_server_close_callback"><code>http.close()</code></a> for details.</p>
<h3>server.listen(handle[, callback])<span><a class="mark" href="#https_server_listen_handle_callback" id="https_server_listen_handle_callback">#</a></span></h3>
<h3>server.listen(path[, callback])<span><a class="mark" href="#https_server_listen_path_callback" id="https_server_listen_path_callback">#</a></span></h3>
<h3>server.listen(port[, host][, backlog][, callback])<span><a class="mark" href="#https_server_listen_port_host_backlog_callback" id="https_server_listen_port_host_backlog_callback">#</a></span></h3>
<p>See <a href="http.html#http_server_listen_port_hostname_backlog_callback"><code>http.listen()</code></a> for details.</p>
<h2>https.get(options, callback)<span><a class="mark" href="#https_https_get_options_callback" id="https_https_get_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.6</span>
</div><p>Like <a href="http.html#http_http_get_options_callback"><code>http.get()</code></a> but for HTTPS.</p>
<p><code>options</code> can be an object or a string. If <code>options</code> is a string, it is
automatically parsed with <a href="url.html#url_url_parse_urlstr_parsequerystring_slashesdenotehost"><code>url.parse()</code></a>.</p>
<p>Example:</p>
<pre><code class="lang-js">const https = require('https');
https.get('https://encrypted.google.com/', (res) => {
console.log('statusCode:', res.statusCode);
console.log('headers:', res.headers);
res.on('data', (d) => {
process.stdout.write(d);
});
}).on('error', (e) => {
console.error(e);
});
</code></pre>
<h2>https.globalAgent<span><a class="mark" href="#https_https_globalagent" id="https_https_globalagent">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><p>Global instance of <a href="#https_class_https_agent"><code>https.Agent</code></a> for all HTTPS client requests.</p>
<h2>https.request(options, callback)<span><a class="mark" href="#https_https_request_options_callback" id="https_https_request_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.6</span>
</div><p>Makes a request to a secure web server.</p>
<p><code>options</code> can be an object or a string. If <code>options</code> is a string, it is
automatically parsed with <a href="url.html#url_url_parse_urlstr_parsequerystring_slashesdenotehost"><code>url.parse()</code></a>.</p>
<p>All options from <a href="http.html#http_http_request_options_callback"><code>http.request()</code></a> are valid.</p>
<p>Example:</p>
<pre><code class="lang-js">const https = require('https');
var options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET'
};
var req = https.request(options, (res) => {
console.log('statusCode:', res.statusCode);
console.log('headers:', res.headers);
res.on('data', (d) => {
process.stdout.write(d);
});
});
req.on('error', (e) => {
console.error(e);
});
req.end();
</code></pre>
<p>The options argument has the following options</p>
<ul>
<li><code>host</code>: A domain name or IP address of the server to issue the request to.
Defaults to <code>'localhost'</code>.</li>
<li><code>hostname</code>: Alias for <code>host</code>. To support <code>url.parse()</code> <code>hostname</code> is
preferred over <code>host</code>.</li>
<li><code>family</code>: IP address family to use when resolving <code>host</code> and <code>hostname</code>.
Valid values are <code>4</code> or <code>6</code>. When unspecified, both IP v4 and v6 will be
used.</li>
<li><code>port</code>: Port of remote server. Defaults to 443.</li>
<li><code>localAddress</code>: Local interface to bind for network connections.</li>
<li><code>socketPath</code>: Unix Domain Socket (use one of host:port or socketPath).</li>
<li><code>method</code>: A string specifying the HTTP request method. Defaults to <code>'GET'</code>.</li>
<li><code>path</code>: Request path. Defaults to <code>'/'</code>. Should include query string if any.
E.G. <code>'/index.html?page=12'</code>. An exception is thrown when the request path
contains illegal characters. Currently, only spaces are rejected but that
may change in the future.</li>
<li><code>headers</code>: An object containing request headers.</li>
<li><code>auth</code>: Basic authentication i.e. <code>'user:password'</code> to compute an
Authorization header.</li>
<li><code>agent</code>: Controls <a href="#https_class_https_agent"><code>Agent</code></a> behavior. When an Agent is used request will
default to <code>Connection: keep-alive</code>. Possible values:<ul>
<li><code>undefined</code> (default): use <a href="#https_https_globalagent"><code>globalAgent</code></a> for this host and port.</li>
<li><code>Agent</code> object: explicitly use the passed in <code>Agent</code>.</li>
<li><code>false</code>: opts out of connection pooling with an Agent, defaults request to
<code>Connection: close</code>.</li>
</ul>
</li>
</ul>
<p>The following options from <a href="#tls_tls_connect_options_callback"><code>tls.connect()</code></a> can also be specified:</p>
<ul>
<li><code>pfx</code>: Certificate, Private key and CA certificates to use for SSL. Default <code>null</code>.</li>
<li><code>key</code>: Private key to use for SSL. Default <code>null</code>.</li>
<li><code>passphrase</code>: A string of passphrase for the private key or pfx. Default <code>null</code>.</li>
<li><code>cert</code>: Public x509 certificate to use. Default <code>null</code>.</li>
<li><code>ca</code>: A string, <a href="buffer.html#buffer_buffer"><code>Buffer</code></a> or array of strings or <a href="buffer.html#buffer_buffer"><code>Buffer</code></a>s of trusted
certificates in PEM format. If this is omitted several well known "root"
CAs will be used, like VeriSign. These are used to authorize connections.</li>
<li><code>ciphers</code>: A string describing the ciphers to use or exclude. Consult
<a href="https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT">https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT</a> for
details on the format.</li>
<li><code>rejectUnauthorized</code>: If <code>true</code>, the server certificate is verified against
the list of supplied CAs. An <code>'error'</code> event is emitted if verification
fails. Verification happens at the connection level, <em>before</em> the HTTP
request is sent. Default <code>true</code>.</li>
<li><code>secureProtocol</code>: The SSL method to use, e.g. <code>SSLv3_method</code> to force
SSL version 3. The possible values depend on your installation of
OpenSSL and are defined in the constant <a href="https://www.openssl.org/docs/ssl/ssl.html#DEALING-WITH-PROTOCOL-METHODS"><code>SSL_METHODS</code></a>.</li>
<li><code>servername</code>: Servername for SNI (Server Name Indication) TLS extension.</li>
</ul>
<p>In order to specify these options, use a custom <a href="#https_class_https_agent"><code>Agent</code></a>.</p>
<p>Example:</p>
<pre><code class="lang-js">var options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET',
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
options.agent = new https.Agent(options);
var req = https.request(options, (res) => {
...
}
</code></pre>
<p>Alternatively, opt out of connection pooling by not using an <code>Agent</code>.</p>
<p>Example:</p>
<pre><code class="lang-js">var options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET',
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem'),
agent: false
};
var req = https.request(options, (res) => {
...
}
</code></pre>
<!-- [end-include:https.md] -->
<!-- [start-include:modules.md] -->
<h1>Modules<span><a class="mark" href="#modules_modules" id="modules_modules">#</a></span></h1>
<pre class="api_stability api_stability_3">Stability: 3 - Locked</pre><!--name=module-->
<p>Node.js has a simple module loading system. In Node.js, files and modules
are in one-to-one correspondence (each file is treated as a separate module).</p>
<p>As an example, consider a file named <code>foo.js</code>:</p>
<pre><code class="lang-js">const circle = require('./circle.js');
console.log(`The area of a circle of radius 4 is ${circle.area(4)}`);
</code></pre>
<p>On the first line, <code>foo.js</code> loads the module <code>circle.js</code> that is in the same
directory as <code>foo.js</code>.</p>
<p>Here are the contents of <code>circle.js</code>:</p>
<pre><code class="lang-js">const PI = Math.PI;
exports.area = (r) => PI * r * r;
exports.circumference = (r) => 2 * PI * r;
</code></pre>
<p>The module <code>circle.js</code> has exported the functions <code>area()</code> and
<code>circumference()</code>. To add functions and objects to the root of your module,
you can add them to the special <code>exports</code> object.</p>
<p>Variables local to the module will be private, because the module is wrapped
in a function by Node.js (see <a href="#modules_the_module_wrapper">module wrapper</a>).
In this example, the variable <code>PI</code> is private to <code>circle.js</code>.</p>
<p>If you want the root of your module's export to be a function (such as a
constructor) or if you want to export a complete object in one assignment
instead of building it one property at a time, assign it to <code>module.exports</code>
instead of <code>exports</code>.</p>
<p>Below, <code>bar.js</code> makes use of the <code>square</code> module, which exports a constructor:</p>
<pre><code class="lang-js">const square = require('./square.js');
var mySquare = square(2);
console.log(`The area of my square is ${mySquare.area()}`);
</code></pre>
<p>The <code>square</code> module is defined in <code>square.js</code>:</p>
<pre><code class="lang-js">// assigning to exports will not modify module, must use module.exports
module.exports = (width) => {
return {
area: () => width * width
};
}
</code></pre>
<p>The module system is implemented in the <code>require("module")</code> module.</p>
<h2>Accessing the main module<span><a class="mark" href="#modules_accessing_the_main_module" id="modules_accessing_the_main_module">#</a></span></h2>
<!-- type=misc -->
<p>When a file is run directly from Node.js, <code>require.main</code> is set to its
<code>module</code>. That means that you can determine whether a file has been run
directly by testing</p>
<pre><code class="lang-js">require.main === module
</code></pre>
<p>For a file <code>foo.js</code>, this will be <code>true</code> if run via <code>node foo.js</code>, but
<code>false</code> if run by <code>require('./foo')</code>.</p>
<p>Because <code>module</code> provides a <code>filename</code> property (normally equivalent to
<code>__filename</code>), the entry point of the current application can be obtained
by checking <code>require.main.filename</code>.</p>
<h2>Addenda: Package Manager Tips<span><a class="mark" href="#modules_addenda_package_manager_tips" id="modules_addenda_package_manager_tips">#</a></span></h2>
<!-- type=misc -->
<p>The semantics of Node.js's <code>require()</code> function were designed to be general
enough to support a number of reasonable directory structures. Package manager
programs such as <code>dpkg</code>, <code>rpm</code>, and <code>npm</code> will hopefully find it possible to
build native packages from Node.js modules without modification.</p>
<p>Below we give a suggested directory structure that could work:</p>
<p>Let's say that we wanted to have the folder at
<code>/usr/lib/node/<some-package>/<some-version></code> hold the contents of a
specific version of a package.</p>
<p>Packages can depend on one another. In order to install package <code>foo</code>, you
may have to install a specific version of package <code>bar</code>. The <code>bar</code> package
may itself have dependencies, and in some cases, these dependencies may even
collide or form cycles.</p>
<p>Since Node.js looks up the <code>realpath</code> of any modules it loads (that is,
resolves symlinks), and then looks for their dependencies in the <code>node_modules</code>
folders as described <a href="#modules_loading_from_node_modules_folders">here</a>, this
situation is very simple to resolve with the following architecture:</p>
<ul>
<li><code>/usr/lib/node/foo/1.2.3/</code> - Contents of the <code>foo</code> package, version 1.2.3.</li>
<li><code>/usr/lib/node/bar/4.3.2/</code> - Contents of the <code>bar</code> package that <code>foo</code>
depends on.</li>
<li><code>/usr/lib/node/foo/1.2.3/node_modules/bar</code> - Symbolic link to
<code>/usr/lib/node/bar/4.3.2/</code>.</li>
<li><code>/usr/lib/node/bar/4.3.2/node_modules/*</code> - Symbolic links to the packages
that <code>bar</code> depends on.</li>
</ul>
<p>Thus, even if a cycle is encountered, or if there are dependency
conflicts, every module will be able to get a version of its dependency
that it can use.</p>
<p>When the code in the <code>foo</code> package does <code>require('bar')</code>, it will get the
version that is symlinked into <code>/usr/lib/node/foo/1.2.3/node_modules/bar</code>.
Then, when the code in the <code>bar</code> package calls <code>require('quux')</code>, it'll get
the version that is symlinked into
<code>/usr/lib/node/bar/4.3.2/node_modules/quux</code>.</p>
<p>Furthermore, to make the module lookup process even more optimal, rather
than putting packages directly in <code>/usr/lib/node</code>, we could put them in
<code>/usr/lib/node_modules/<name>/<version></code>. Then Node.js will not bother
looking for missing dependencies in <code>/usr/node_modules</code> or <code>/node_modules</code>.</p>
<p>In order to make modules available to the Node.js REPL, it might be useful to
also add the <code>/usr/lib/node_modules</code> folder to the <code>$NODE_PATH</code> environment
variable. Since the module lookups using <code>node_modules</code> folders are all
relative, and based on the real path of the files making the calls to
<code>require()</code>, the packages themselves can be anywhere.</p>
<h2>All Together...<span><a class="mark" href="#modules_all_together" id="modules_all_together">#</a></span></h2>
<!-- type=misc -->
<p>To get the exact filename that will be loaded when <code>require()</code> is called, use
the <code>require.resolve()</code> function.</p>
<p>Putting together all of the above, here is the high-level algorithm
in pseudocode of what require.resolve does:</p>
<pre><code>require(X) from module at path Y
1. If X is a core module,
a. return the core module
b. STOP
2. If X begins with './' or '/' or '../'
a. LOAD_AS_FILE(Y + X)
b. LOAD_AS_DIRECTORY(Y + X)
3. LOAD_NODE_MODULES(X, dirname(Y))
4. THROW "not found"
LOAD_AS_FILE(X)
1. If X is a file, load X as JavaScript text. STOP
2. If X.js is a file, load X.js as JavaScript text. STOP
3. If X.json is a file, parse X.json to a JavaScript Object. STOP
4. If X.node is a file, load X.node as binary addon. STOP
LOAD_AS_DIRECTORY(X)
1. If X/package.json is a file,
a. Parse X/package.json, and look for "main" field.
b. let M = X + (json main field)
c. LOAD_AS_FILE(M)
2. If X/index.js is a file, load X/index.js as JavaScript text. STOP
3. If X/index.json is a file, parse X/index.json to a JavaScript object. STOP
4. If X/index.node is a file, load X/index.node as binary addon. STOP
LOAD_NODE_MODULES(X, START)
1. let DIRS=NODE_MODULES_PATHS(START)
2. for each DIR in DIRS:
a. LOAD_AS_FILE(DIR/X)
b. LOAD_AS_DIRECTORY(DIR/X)
NODE_MODULES_PATHS(START)
1. let PARTS = path split(START)
2. let I = count of PARTS - 1
3. let DIRS = []
4. while I >= 0,
a. if PARTS[I] = "node_modules" CONTINUE
b. DIR = path join(PARTS[0 .. I] + "node_modules")
c. DIRS = DIRS + DIR
d. let I = I - 1
5. return DIRS
</code></pre><h2>Caching<span><a class="mark" href="#modules_caching" id="modules_caching">#</a></span></h2>
<!--type=misc-->
<p>Modules are cached after the first time they are loaded. This means
(among other things) that every call to <code>require('foo')</code> will get
exactly the same object returned, if it would resolve to the same file.</p>
<p>Multiple calls to <code>require('foo')</code> may not cause the module code to be
executed multiple times. This is an important feature. With it,
"partially done" objects can be returned, thus allowing transitive
dependencies to be loaded even when they would cause cycles.</p>
<p>If you want to have a module execute code multiple times, then export a
function, and call that function.</p>
<h3>Module Caching Caveats<span><a class="mark" href="#modules_module_caching_caveats" id="modules_module_caching_caveats">#</a></span></h3>
<!--type=misc-->
<p>Modules are cached based on their resolved filename. Since modules may
resolve to a different filename based on the location of the calling
module (loading from <code>node_modules</code> folders), it is not a <em>guarantee</em>
that <code>require('foo')</code> will always return the exact same object, if it
would resolve to different files.</p>
<p>Additionally, on case-insensitive file systems or operating systems, different
resolved filenames can point to the same file, but the cache will still treat
them as different modules and will reload the file multiple times. For example,
<code>require('./foo')</code> and <code>require('./FOO')</code> return two different objects,
irrespective of whether or not <code>./foo</code> and <code>./FOO</code> are the same file.</p>
<h2>Core Modules<span><a class="mark" href="#modules_core_modules" id="modules_core_modules">#</a></span></h2>
<!--type=misc-->
<p>Node.js has several modules compiled into the binary. These modules are
described in greater detail elsewhere in this documentation.</p>
<p>The core modules are defined within Node.js's source and are located in the
<code>lib/</code> folder.</p>
<p>Core modules are always preferentially loaded if their identifier is
passed to <code>require()</code>. For instance, <code>require('http')</code> will always
return the built in HTTP module, even if there is a file by that name.</p>
<h2>Cycles<span><a class="mark" href="#modules_cycles" id="modules_cycles">#</a></span></h2>
<!--type=misc-->
<p>When there are circular <code>require()</code> calls, a module might not have finished
executing when it is returned.</p>
<p>Consider this situation:</p>
<p><code>a.js</code>:</p>
<pre><code>console.log('a starting');
exports.done = false;
const b = require('./b.js');
console.log('in a, b.done = %j', b.done);
exports.done = true;
console.log('a done');
</code></pre><p><code>b.js</code>:</p>
<pre><code>console.log('b starting');
exports.done = false;
const a = require('./a.js');
console.log('in b, a.done = %j', a.done);
exports.done = true;
console.log('b done');
</code></pre><p><code>main.js</code>:</p>
<pre><code>console.log('main starting');
const a = require('./a.js');
const b = require('./b.js');
console.log('in main, a.done=%j, b.done=%j', a.done, b.done);
</code></pre><p>When <code>main.js</code> loads <code>a.js</code>, then <code>a.js</code> in turn loads <code>b.js</code>. At that
point, <code>b.js</code> tries to load <code>a.js</code>. In order to prevent an infinite
loop, an <strong>unfinished copy</strong> of the <code>a.js</code> exports object is returned to the
<code>b.js</code> module. <code>b.js</code> then finishes loading, and its <code>exports</code> object is
provided to the <code>a.js</code> module.</p>
<p>By the time <code>main.js</code> has loaded both modules, they're both finished.
The output of this program would thus be:</p>
<pre><code>$ node main.js
main starting
a starting
b starting
in b, a.done = false
b done
in a, b.done = true
a done
in main, a.done=true, b.done=true
</code></pre><p>If you have cyclic module dependencies in your program, make sure to
plan accordingly.</p>
<h2>File Modules<span><a class="mark" href="#modules_file_modules" id="modules_file_modules">#</a></span></h2>
<!--type=misc-->
<p>If the exact filename is not found, then Node.js will attempt to load the
required filename with the added extensions: <code>.js</code>, <code>.json</code>, and finally
<code>.node</code>.</p>
<p><code>.js</code> files are interpreted as JavaScript text files, and <code>.json</code> files are
parsed as JSON text files. <code>.node</code> files are interpreted as compiled addon
modules loaded with <code>dlopen</code>.</p>
<p>A required module prefixed with <code>'/'</code> is an absolute path to the file. For
example, <code>require('/home/marco/foo.js')</code> will load the file at
<code>/home/marco/foo.js</code>.</p>
<p>A required module prefixed with <code>'./'</code> is relative to the file calling
<code>require()</code>. That is, <code>circle.js</code> must be in the same directory as <code>foo.js</code> for
<code>require('./circle')</code> to find it.</p>
<p>Without a leading '/', './', or '../' to indicate a file, the module must
either be a core module or is loaded from a <code>node_modules</code> folder.</p>
<p>If the given path does not exist, <code>require()</code> will throw an <a href="errors.html#errors_class_error"><code>Error</code></a> with its
<code>code</code> property set to <code>'MODULE_NOT_FOUND'</code>.</p>
<h2>Folders as Modules<span><a class="mark" href="#modules_folders_as_modules" id="modules_folders_as_modules">#</a></span></h2>
<!--type=misc-->
<p>It is convenient to organize programs and libraries into self-contained
directories, and then provide a single entry point to that library.
There are three ways in which a folder may be passed to <code>require()</code> as
an argument.</p>
<p>The first is to create a <code>package.json</code> file in the root of the folder,
which specifies a <code>main</code> module. An example package.json file might
look like this:</p>
<pre><code>{ "name" : "some-library",
"main" : "./lib/some-library.js" }
</code></pre><p>If this was in a folder at <code>./some-library</code>, then
<code>require('./some-library')</code> would attempt to load
<code>./some-library/lib/some-library.js</code>.</p>
<p>This is the extent of Node.js's awareness of package.json files.</p>
<p>Note: If the file specified by the <code>"main"</code> entry of <code>package.json</code> is missing
and can not be resolved, Node.js will report the entire module as missing with
the default error:</p>
<pre><code>Error: Cannot find module 'some-library'
</code></pre><p>If there is no package.json file present in the directory, then Node.js
will attempt to load an <code>index.js</code> or <code>index.node</code> file out of that
directory. For example, if there was no package.json file in the above
example, then <code>require('./some-library')</code> would attempt to load:</p>
<ul>
<li><code>./some-library/index.js</code></li>
<li><code>./some-library/index.node</code></li>
</ul>
<h2>Loading from <code>node_modules</code> Folders<span><a class="mark" href="#modules_loading_from_node_modules_folders" id="modules_loading_from_node_modules_folders">#</a></span></h2>
<!--type=misc-->
<p>If the module identifier passed to <code>require()</code> is not a
<a href="#modules_core_modules">core</a> module, and does not begin with <code>'/'</code>, <code>'../'</code>, or
<code>'./'</code>, then Node.js starts at the parent directory of the current module, and
adds <code>/node_modules</code>, and attempts to load the module from that location. Node
will not append <code>node_modules</code> to a path already ending in <code>node_modules</code>.</p>
<p>If it is not found there, then it moves to the parent directory, and so
on, until the root of the file system is reached.</p>
<p>For example, if the file at <code>'/home/ry/projects/foo.js'</code> called
<code>require('bar.js')</code>, then Node.js would look in the following locations, in
this order:</p>
<ul>
<li><code>/home/ry/projects/node_modules/bar.js</code></li>
<li><code>/home/ry/node_modules/bar.js</code></li>
<li><code>/home/node_modules/bar.js</code></li>
<li><code>/node_modules/bar.js</code></li>
</ul>
<p>This allows programs to localize their dependencies, so that they do not
clash.</p>
<p>You can require specific files or sub modules distributed with a module by
including a path suffix after the module name. For instance
<code>require('example-module/path/to/file')</code> would resolve <code>path/to/file</code>
relative to where <code>example-module</code> is located. The suffixed path follows the
same module resolution semantics.</p>
<h2>Loading from the global folders<span><a class="mark" href="#modules_loading_from_the_global_folders" id="modules_loading_from_the_global_folders">#</a></span></h2>
<!-- type=misc -->
<p>If the <code>NODE_PATH</code> environment variable is set to a colon-delimited list
of absolute paths, then Node.js will search those paths for modules if they
are not found elsewhere. (Note: On Windows, <code>NODE_PATH</code> is delimited by
semicolons instead of colons.)</p>
<p><code>NODE_PATH</code> was originally created to support loading modules from
varying paths before the current <a href="#modules_all_together">module resolution</a> algorithm was frozen.</p>
<p><code>NODE_PATH</code> is still supported, but is less necessary now that the Node.js
ecosystem has settled on a convention for locating dependent modules.
Sometimes deployments that rely on <code>NODE_PATH</code> show surprising behavior
when people are unaware that <code>NODE_PATH</code> must be set. Sometimes a
module's dependencies change, causing a different version (or even a
different module) to be loaded as the <code>NODE_PATH</code> is searched.</p>
<p>Additionally, Node.js will search in the following locations:</p>
<ul>
<li>1: <code>$HOME/.node_modules</code></li>
<li>2: <code>$HOME/.node_libraries</code></li>
<li>3: <code>$PREFIX/lib/node</code></li>
</ul>
<p>Where <code>$HOME</code> is the user's home directory, and <code>$PREFIX</code> is Node.js's
configured <code>node_prefix</code>.</p>
<p>These are mostly for historic reasons. <strong>You are highly encouraged
to place your dependencies locally in <code>node_modules</code> folders.</strong> They
will be loaded faster, and more reliably.</p>
<h2>The module wrapper<span><a class="mark" href="#modules_the_module_wrapper" id="modules_the_module_wrapper">#</a></span></h2>
<!-- type=misc -->
<p>Before a module's code is executed, Node.js will wrap it with a function
wrapper that looks like the following:</p>
<pre><code class="lang-js">(function (exports, require, module, __filename, __dirname) {
// Your module code actually lives in here
});
</code></pre>
<p>By doing this, Node.js achieves a few things:</p>
<ul>
<li>It keeps top-level variables (defined with <code>var</code>, <code>const</code> or <code>let</code>) scoped to
the module rather than the global object.</li>
<li>It helps to provide some global-looking variables that are actually specific
to the module, such as:<ul>
<li>The <code>module</code> and <code>exports</code> objects that the implementor can use to export
values from the module.</li>
<li>The convenience variables <code>__filename</code> and <code>__dirname</code>, containing the
module's absolute filename and directory path.</li>
</ul>
</li>
</ul>
<h2>The <code>module</code> Object<span><a class="mark" href="#modules_the_module_object" id="modules_the_module_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><!-- type=var -->
<!-- name=module -->
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>In each module, the <code>module</code> free variable is a reference to the object
representing the current module. For convenience, <code>module.exports</code> is
also accessible via the <code>exports</code> module-global. <code>module</code> isn't actually
a global but rather local to each module.</p>
<h3>module.children<span><a class="mark" href="#modules_module_children" id="modules_module_children">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a></li>
</ul>
<p>The module objects required by this one.</p>
<h3>module.exports<span><a class="mark" href="#modules_module_exports" id="modules_module_exports">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>The <code>module.exports</code> object is created by the Module system. Sometimes this is
not acceptable; many want their module to be an instance of some class. To do
this, assign the desired export object to <code>module.exports</code>. Note that assigning
the desired object to <code>exports</code> will simply rebind the local <code>exports</code> variable,
which is probably not what you want to do.</p>
<p>For example suppose we were making a module called <code>a.js</code></p>
<pre><code class="lang-js">const EventEmitter = require('events');
module.exports = new EventEmitter();
// Do some work, and after some time emit
// the 'ready' event from the module itself.
setTimeout(() => {
module.exports.emit('ready');
}, 1000);
</code></pre>
<p>Then in another file we could do</p>
<pre><code class="lang-js">const a = require('./a');
a.on('ready', () => {
console.log('module a is ready');
});
</code></pre>
<p>Note that assignment to <code>module.exports</code> must be done immediately. It cannot be
done in any callbacks. This does not work:</p>
<p>x.js:</p>
<pre><code class="lang-js">setTimeout(() => {
module.exports = { a: 'hello' };
}, 0);
</code></pre>
<p>y.js:</p>
<pre><code class="lang-js">const x = require('./x');
console.log(x.a);
</code></pre>
<h4>exports shortcut<span><a class="mark" href="#modules_exports_shortcut" id="modules_exports_shortcut">#</a></span></h4>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><p>The <code>exports</code> variable is available within a module's file-level scope, and is
assigned the value of <code>module.exports</code> before the module is evaluated.</p>
<p>It allows a shortcut, so that <code>module.exports.f = ...</code> can be written more
succinctly as <code>exports.f = ...</code>. However, be aware that like any variable, if a
new value is assigned to <code>exports</code>, it is no longer bound to <code>module.exports</code>:</p>
<pre><code class="lang-js">module.exports.hello = true; // Exported from require of module
exports = { hello: false }; // Not exported, only available in the module
</code></pre>
<p>When the <code>module.exports</code> property is being completely replaced by a new
object, it is common to also reassign <code>exports</code>, for example:</p>
<pre><code class="lang-js">module.exports = exports = function Constructor() {
// ... etc.
</code></pre>
<p>To illustrate the behavior, imagine this hypothetical implementation of
<code>require()</code>, which is quite similar to what is actually done by <code>require()</code>:</p>
<pre><code class="lang-js">function require(...) {
var module = { exports: {} };
((module, exports) => {
// Your module code here. In this example, define a function.
function some_func() {};
exports = some_func;
// At this point, exports is no longer a shortcut to module.exports, and
// this module will still export an empty default object.
module.exports = some_func;
// At this point, the module will now export some_func, instead of the
// default object.
})(module, module.exports);
return module.exports;
}
</code></pre>
<h3>module.filename<span><a class="mark" href="#modules_module_filename" id="modules_module_filename">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
<p>The fully resolved filename to the module.</p>
<h3>module.id<span><a class="mark" href="#modules_module_id" id="modules_module_id">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
</ul>
<p>The identifier for the module. Typically this is the fully resolved
filename.</p>
<h3>module.loaded<span><a class="mark" href="#modules_module_loaded" id="modules_module_loaded">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>Whether or not the module is done loading, or is in the process of
loading.</p>
<h3>module.parent<span><a class="mark" href="#modules_module_parent" id="modules_module_parent">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Module object</li>
</ul>
<p>The module that first required this one.</p>
<h3>module.require(id)<span><a class="mark" href="#modules_module_require_id" id="modules_module_require_id">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.1</span>
</div><ul>
<li><code>id</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> <code>module.exports</code> from the resolved module</li>
</ul>
<p>The <code>module.require</code> method provides a way to load a module as if
<code>require()</code> was called from the original module.</p>
<p>Note that in order to do this, you must get a reference to the <code>module</code>
object. Since <code>require()</code> returns the <code>module.exports</code>, and the <code>module</code> is
typically <em>only</em> available within a specific module's code, it must be
explicitly exported in order to be used.</p>
<!-- [end-include:modules.md] -->
<!-- [start-include:net.md] -->
<h1>Net<span><a class="mark" href="#net_net" id="net_net">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>The <code>net</code> module provides you with an asynchronous network wrapper. It contains
functions for creating both servers and clients (called streams). You can include
this module with <code>require('net');</code>.</p>
<h2>Class: net.Server<span><a class="mark" href="#net_class_net_server" id="net_class_net_server">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>This class is used to create a TCP or local server.</p>
<p><code>net.Server</code> is an <a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a> with the following events:</p>
<h3>Event: 'close'<span><a class="mark" href="#net_event_close" id="net_event_close">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Emitted when the server closes. Note that if connections exist, this
event is not emitted until all connections are ended.</p>
<h3>Event: 'connection'<span><a class="mark" href="#net_event_connection" id="net_event_connection">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><a href="net.html#net_class_net_socket" class="type"><net.Socket></a> The connection object</li>
</ul>
<p>Emitted when a new connection is made. <code>socket</code> is an instance of
<code>net.Socket</code>.</p>
<h3>Event: 'error'<span><a class="mark" href="#net_event_error" id="net_event_error">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Emitted when an error occurs. Unlike <a href="net.html#net_class_net_socket"><code>net.Socket</code></a>, the <a href="#net_event_close"><code>'close'</code></a>
event will <strong>not</strong> be emitted directly following this event unless
<a href="#net_server_close_callback"><code>server.close()</code></a> is manually called. See the example in discussion of
<a href="#net_server_listen_port_hostname_backlog_callback"><code>server.listen()</code></a>.</p>
<h3>Event: 'listening'<span><a class="mark" href="#net_event_listening" id="net_event_listening">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Emitted when the server has been bound after calling <code>server.listen</code>.</p>
<h3>server.address()<span><a class="mark" href="#net_server_address" id="net_server_address">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Returns the bound address, the address family name, and port of the server
as reported by the operating system.
Useful to find which port was assigned when getting an OS-assigned address.
Returns an object with <code>port</code>, <code>family</code>, and <code>address</code> properties:
<code>{ port: 12346, family: 'IPv4', address: '127.0.0.1' }</code></p>
<p>Example:</p>
<pre><code class="lang-js">var server = net.createServer((socket) => {
socket.end('goodbye\n');
}).on('error', (err) => {
// handle errors here
throw err;
});
// grab a random port.
server.listen(() => {
console.log('opened server on', server.address());
});
</code></pre>
<p>Don't call <code>server.address()</code> until the <code>'listening'</code> event has been emitted.</p>
<h3>server.close([callback])<span><a class="mark" href="#net_server_close_callback" id="net_server_close_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Stops the server from accepting new connections and keeps existing
connections. This function is asynchronous, the server is finally
closed when all connections are ended and the server emits a <a href="#net_event_close"><code>'close'</code></a> event.
The optional <code>callback</code> will be called once the <code>'close'</code> event occurs. Unlike
that event, it will be called with an Error as its only argument if the server
was not open when it was closed.</p>
<h3>server.connections<span><a class="mark" href="#net_server_connections" id="net_server_connections">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.2.0</span>
<span>Deprecated since: v0.9.7 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="#net_server_getconnections_callback"><code>server.getConnections()</code></a> instead.</pre><p>The number of concurrent connections on the server.</p>
<p>This becomes <code>null</code> when sending a socket to a child with
<a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a>. To poll forks and get current number of active
connections use asynchronous <code>server.getConnections</code> instead.</p>
<h3>server.getConnections(callback)<span><a class="mark" href="#net_server_getconnections_callback" id="net_server_getconnections_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.7</span>
</div><p>Asynchronously get the number of concurrent connections on the server. Works
when sockets were sent to forks.</p>
<p>Callback should take two arguments <code>err</code> and <code>count</code>.</p>
<h3>server.listen(handle[, backlog][, callback])<span><a class="mark" href="#net_server_listen_handle_backlog_callback" id="net_server_listen_handle_backlog_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.10</span>
</div><ul>
<li><code>handle</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>backlog</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>The <code>handle</code> object can be set to either a server or socket (anything
with an underlying <code>_handle</code> member), or a <code>{fd: <n>}</code> object.</p>
<p>This will cause the server to accept connections on the specified
handle, but it is presumed that the file descriptor or handle has
already been bound to a port or domain socket.</p>
<p>Listening on a file descriptor is not supported on Windows.</p>
<p>This function is asynchronous. When the server has been bound,
<a href="#net_event_listening"><code>'listening'</code></a> event will be emitted.
The last parameter <code>callback</code> will be added as a listener for the
<a href="#net_event_listening"><code>'listening'</code></a> event.</p>
<p>The parameter <code>backlog</code> behaves the same as in
<a href="#net_server_listen_port_hostname_backlog_callback"><code>server.listen([port][, hostname][, backlog][, callback])</code></a>.</p>
<h3>server.listen(options[, callback])<span><a class="mark" href="#net_server_listen_options_callback" id="net_server_listen_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> - Required. Supports the following properties:<ul>
<li><code>port</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> - Optional.</li>
<li><code>host</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - Optional.</li>
<li><code>backlog</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> - Optional.</li>
<li><code>path</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> - Optional.</li>
<li><code>exclusive</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> - Optional.</li>
</ul>
</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> - Optional.</li>
</ul>
<p>The <code>port</code>, <code>host</code>, and <code>backlog</code> properties of <code>options</code>, as well as the
optional callback function, behave as they do on a call to
<a href="#net_server_listen_port_hostname_backlog_callback"><code>server.listen([port][, hostname][, backlog][, callback])</code></a>.
Alternatively, the <code>path</code> option can be used to specify a UNIX socket.</p>
<p>If <code>exclusive</code> is <code>false</code> (default), then cluster workers will use the same
underlying handle, allowing connection handling duties to be shared. When
<code>exclusive</code> is <code>true</code>, the handle is not shared, and attempted port sharing
results in an error. An example which listens on an exclusive port is
shown below.</p>
<pre><code class="lang-js">server.listen({
host: 'localhost',
port: 80,
exclusive: true
});
</code></pre>
<h3>server.listen(path[, backlog][, callback])<span><a class="mark" href="#net_server_listen_path_backlog_callback" id="net_server_listen_path_backlog_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><code>path</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
<li><code>backlog</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Start a local socket server listening for connections on the given <code>path</code>.</p>
<p>This function is asynchronous. When the server has been bound,
<a href="#net_event_listening"><code>'listening'</code></a> event will be emitted. The last parameter <code>callback</code>
will be added as a listener for the <a href="#net_event_listening"><code>'listening'</code></a> event.</p>
<p>On UNIX, the local domain is usually known as the UNIX domain. The path is a
filesystem path name. It gets truncated to <code>sizeof(sockaddr_un.sun_path)</code>
bytes, decreased by 1. It varies on different operating system between 91 and
107 bytes. The typical values are 107 on Linux and 103 on OS X. The path is
subject to the same naming conventions and permissions checks as would be done
on file creation, will be visible in the filesystem, and will <em>persist until
unlinked</em>.</p>
<p>On Windows, the local domain is implemented using a named pipe. The path <em>must</em>
refer to an entry in <code>\\?\pipe\</code> or <code>\\.\pipe\</code>. Any characters are permitted,
but the latter may do some processing of pipe names, such as resolving <code>..</code>
sequences. Despite appearances, the pipe name space is flat. Pipes will <em>not
persist</em>, they are removed when the last reference to them is closed. Do not
forget JavaScript string escaping requires paths to be specified with
double-backslashes, such as:</p>
<pre><code>net.createServer().listen(
path.join('\\\\?\\pipe', process.cwd(), 'myctl'))
</code></pre><p>The parameter <code>backlog</code> behaves the same as in
<a href="#net_server_listen_port_hostname_backlog_callback"><code>server.listen([port][, hostname][, backlog][, callback])</code></a>.</p>
<h3>server.listen([port][, hostname][, backlog][, callback])<span><a class="mark" href="#net_server_listen_port_hostname_backlog_callback" id="net_server_listen_port_hostname_backlog_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Begin accepting connections on the specified <code>port</code> and <code>hostname</code>. If the
<code>hostname</code> is omitted, the server will accept connections on any IPv6 address
(<code>::</code>) when IPv6 is available, or any IPv4 address (<code>0.0.0.0</code>) otherwise.
Omit the port argument, or use a port value of <code>0</code>, to have the operating system
assign a random port, which can be retrieved by using <code>server.address().port</code>
after the <code>'listening'</code> event has been emitted.</p>
<p>Backlog is the maximum length of the queue of pending connections.
The actual length will be determined by the OS through sysctl settings such as
<code>tcp_max_syn_backlog</code> and <code>somaxconn</code> on Linux. The default value of this
parameter is 511 (not 512).</p>
<p>This function is asynchronous. When the server has been bound,
<a href="#net_event_listening"><code>'listening'</code></a> event will be emitted. The last parameter <code>callback</code>
will be added as a listener for the <a href="#net_event_listening"><code>'listening'</code></a> event.</p>
<p>One issue some users run into is getting <code>EADDRINUSE</code> errors. This means that
another server is already running on the requested port. One way of handling this
would be to wait a second and then try again:</p>
<pre><code class="lang-js">server.on('error', (e) => {
if (e.code == 'EADDRINUSE') {
console.log('Address in use, retrying...');
setTimeout(() => {
server.close();
server.listen(PORT, HOST);
}, 1000);
}
});
</code></pre>
<p>(Note: All sockets in Node.js are set <code>SO_REUSEADDR</code>.)</p>
<h3>server.maxConnections<span><a class="mark" href="#net_server_maxconnections" id="net_server_maxconnections">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.2.0</span>
</div><p>Set this property to reject connections when the server's connection count gets
high.</p>
<p>It is not recommended to use this option once a socket has been sent to a child
with <a href="child_process.html#child_process_child_process_fork_modulepath_args_options"><code>child_process.fork()</code></a>.</p>
<h3>server.ref()<span><a class="mark" href="#net_server_ref" id="net_server_ref">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>Opposite of <code>unref</code>, calling <code>ref</code> on a previously <code>unref</code>d server will <em>not</em>
let the program exit if it's the only server left (the default behavior). If
the server is <code>ref</code>d calling <code>ref</code> again will have no effect.</p>
<p>Returns <code>server</code>.</p>
<h3>server.unref()<span><a class="mark" href="#net_server_unref" id="net_server_unref">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>Calling <code>unref</code> on a server will allow the program to exit if this is the only
active server in the event system. If the server is already <code>unref</code>d calling
<code>unref</code> again will have no effect.</p>
<p>Returns <code>server</code>.</p>
<h2>Class: net.Socket<span><a class="mark" href="#net_class_net_socket" id="net_class_net_socket">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><p>This object is an abstraction of a TCP or local socket. <code>net.Socket</code>
instances implement a duplex Stream interface. They can be created by the
user and used as a client (with <a href="#net_socket_connect_options_connectlistener"><code>connect()</code></a>) or they can be created by Node.js
and passed to the user through the <code>'connection'</code> event of a server.</p>
<h3>new net.Socket(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#net_new_net_socket_options" id="net_new_net_socket_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><p>Construct a new socket object.</p>
<p><code>options</code> is an object with the following defaults:</p>
<pre><code class="lang-js">{
fd: null,
allowHalfOpen: false,
readable: false,
writable: false
}
</code></pre>
<p><code>fd</code> allows you to specify the existing file descriptor of socket.
Set <code>readable</code> and/or <code>writable</code> to <code>true</code> to allow reads and/or writes on this
socket (NOTE: Works only when <code>fd</code> is passed).
About <code>allowHalfOpen</code>, refer to <code>createServer()</code> and <code>'end'</code> event.</p>
<p><code>net.Socket</code> instances are <a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a> with the following events:</p>
<h3>Event: 'close'<span><a class="mark" href="#net_event_close_1" id="net_event_close_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><code>had_error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> <code>true</code> if the socket had a transmission error.</li>
</ul>
<p>Emitted once the socket is fully closed. The argument <code>had_error</code> is a boolean
which says if the socket was closed due to a transmission error.</p>
<h3>Event: 'connect'<span><a class="mark" href="#net_event_connect" id="net_event_connect">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Emitted when a socket connection is successfully established.
See <a href="#net_socket_connect_options_connectlistener"><code>connect()</code></a>.</p>
<h3>Event: 'data'<span><a class="mark" href="#net_event_data" id="net_event_data">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a></li>
</ul>
<p>Emitted when data is received. The argument <code>data</code> will be a <code>Buffer</code> or
<code>String</code>. Encoding of data is set by <code>socket.setEncoding()</code>.
(See the <a href="stream.html#stream_class_stream_readable">Readable Stream</a> section for more information.)</p>
<p>Note that the <strong>data will be lost</strong> if there is no listener when a <code>Socket</code>
emits a <code>'data'</code> event.</p>
<h3>Event: 'drain'<span><a class="mark" href="#net_event_drain" id="net_event_drain">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Emitted when the write buffer becomes empty. Can be used to throttle uploads.</p>
<p>See also: the return values of <code>socket.write()</code></p>
<h3>Event: 'end'<span><a class="mark" href="#net_event_end" id="net_event_end">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Emitted when the other end of the socket sends a FIN packet.</p>
<p>By default (<code>allowHalfOpen == false</code>) the socket will destroy its file
descriptor once it has written out its pending write queue. However, by
setting <code>allowHalfOpen == true</code> the socket will not automatically <code>end()</code>
its side allowing the user to write arbitrary amounts of data, with the
caveat that the user is required to <code>end()</code> their side now.</p>
<h3>Event: 'error'<span><a class="mark" href="#net_event_error_1" id="net_event_error_1">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Emitted when an error occurs. The <code>'close'</code> event will be called directly
following this event.</p>
<h3>Event: 'lookup'<span><a class="mark" href="#net_event_lookup" id="net_event_lookup">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.3</span>
</div><p>Emitted after resolving the hostname but before connecting.
Not applicable to UNIX sockets.</p>
<ul>
<li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><Null></a> The error object. See <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>.</li>
<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The IP address.</li>
<li><code>family</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><Null></a> The address type. See <a href="dns.html#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>.</li>
</ul>
<h3>Event: 'timeout'<span><a class="mark" href="#net_event_timeout" id="net_event_timeout">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Emitted if the socket times out from inactivity. This is only to notify that
the socket has been idle. The user must manually close the connection.</p>
<p>See also: <a href="#net_socket_settimeout_timeout_callback"><code>socket.setTimeout()</code></a></p>
<h3>socket.address()<span><a class="mark" href="#net_socket_address" id="net_socket_address">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Returns the bound address, the address family name and port of the
socket as reported by the operating system. Returns an object with
three properties, e.g.
<code>{ port: 12346, family: 'IPv4', address: '127.0.0.1' }</code></p>
<h3>socket.bufferSize<span><a class="mark" href="#net_socket_buffersize" id="net_socket_buffersize">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.8</span>
</div><p><code>net.Socket</code> has the property that <code>socket.write()</code> always works. This is to
help users get up and running quickly. The computer cannot always keep up
with the amount of data that is written to a socket - the network connection
simply might be too slow. Node.js will internally queue up the data written to a
socket and send it out over the wire when it is possible. (Internally it is
polling on the socket's file descriptor for being writable).</p>
<p>The consequence of this internal buffering is that memory may grow. This
property shows the number of characters currently buffered to be written.
(Number of characters is approximately equal to the number of bytes to be
written, but the buffer may contain strings, and the strings are lazily
encoded, so the exact number of bytes is not known.)</p>
<p>Users who experience large or growing <code>bufferSize</code> should attempt to
"throttle" the data flows in their program with <a href="#net_socket_pause"><code>pause()</code></a> and <a href="#net_socket_resume"><code>resume()</code></a>.</p>
<h3>socket.bytesRead<span><a class="mark" href="#net_socket_bytesread" id="net_socket_bytesread">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.3</span>
</div><p>The amount of received bytes.</p>
<h3>socket.bytesWritten<span><a class="mark" href="#net_socket_byteswritten" id="net_socket_byteswritten">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.3</span>
</div><p>The amount of bytes sent.</p>
<h3>socket.connect(options[, connectListener])<span><a class="mark" href="#net_socket_connect_options_connectlistener" id="net_socket_connect_options_connectlistener">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Opens the connection for a given socket.</p>
<p>For TCP sockets, <code>options</code> argument should be an object which specifies:</p>
<ul>
<li><p><code>port</code>: Port the client should connect to (Required).</p>
</li>
<li><p><code>host</code>: Host the client should connect to. Defaults to <code>'localhost'</code>.</p>
</li>
<li><p><code>localAddress</code>: Local interface to bind to for network connections.</p>
</li>
<li><p><code>localPort</code>: Local port to bind to for network connections.</p>
</li>
<li><p><code>family</code> : Version of IP stack. Defaults to <code>4</code>.</p>
</li>
<li><p><code>lookup</code> : Custom lookup function. Defaults to <code>dns.lookup</code>.</p>
</li>
</ul>
<p>For local domain sockets, <code>options</code> argument should be an object which
specifies:</p>
<ul>
<li><code>path</code>: Path the client should connect to (Required).</li>
</ul>
<p>Normally this method is not needed, as <code>net.createConnection</code> opens the
socket. Use this only if you are implementing a custom Socket.</p>
<p>This function is asynchronous. When the <a href="#net_event_connect"><code>'connect'</code></a> event is emitted the
socket is established. If there is a problem connecting, the <code>'connect'</code> event
will not be emitted, the <a href="#net_event_error_1"><code>'error'</code></a> event will be emitted with the exception.</p>
<p>The <code>connectListener</code> parameter will be added as a listener for the
<a href="#net_event_connect"><code>'connect'</code></a> event.</p>
<h3>socket.connect(path[, connectListener])<span><a class="mark" href="#net_socket_connect_path_connectlistener" id="net_socket_connect_path_connectlistener">#</a></span></h3>
<h3>socket.connect(port[, host][, connectListener])<span><a class="mark" href="#net_socket_connect_port_host_connectlistener" id="net_socket_connect_port_host_connectlistener">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>As <a href="#net_socket_connect_options_connectlistener"><code>socket.connect(options\[, connectListener\])</code></a>,
with options either as either <code>{port: port, host: host}</code> or <code>{path: path}</code>.</p>
<h3>socket.destroy()<span><a class="mark" href="#net_socket_destroy" id="net_socket_destroy">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Ensures that no more I/O activity happens on this socket. Only necessary in
case of errors (parse error or so).</p>
<h3>socket.destroyed<span><a class="mark" href="#net_socket_destroyed" id="net_socket_destroyed">#</a></span></h3>
<p>A Boolean value that indicates if the connection is destroyed or not. Once a
connection is destroyed no further data can be transferred using it.</p>
<h3>socket.end([data][, encoding])<span><a class="mark" href="#net_socket_end_data_encoding" id="net_socket_end_data_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Half-closes the socket. i.e., it sends a FIN packet. It is possible the
server will still send some data.</p>
<p>If <code>data</code> is specified, it is equivalent to calling
<code>socket.write(data, encoding)</code> followed by <code>socket.end()</code>.</p>
<h3>socket.localAddress<span><a class="mark" href="#net_socket_localaddress" id="net_socket_localaddress">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.6</span>
</div><p>The string representation of the local IP address the remote client is
connecting on. For example, if you are listening on <code>'0.0.0.0'</code> and the
client connects on <code>'192.168.1.1'</code>, the value would be <code>'192.168.1.1'</code>.</p>
<h3>socket.localPort<span><a class="mark" href="#net_socket_localport" id="net_socket_localport">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.6</span>
</div><p>The numeric representation of the local port. For example,
<code>80</code> or <code>21</code>.</p>
<h3>socket.pause()<span><a class="mark" href="#net_socket_pause" id="net_socket_pause">#</a></span></h3>
<p>Pauses the reading of data. That is, <a href="#stream_event_data"><code>'data'</code></a> events will not be emitted.
Useful to throttle back an upload.</p>
<h3>socket.ref()<span><a class="mark" href="#net_socket_ref" id="net_socket_ref">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>Opposite of <code>unref</code>, calling <code>ref</code> on a previously <code>unref</code>d socket will <em>not</em>
let the program exit if it's the only socket left (the default behavior). If
the socket is <code>ref</code>d calling <code>ref</code> again will have no effect.</p>
<p>Returns <code>socket</code>.</p>
<h3>socket.remoteAddress<span><a class="mark" href="#net_socket_remoteaddress" id="net_socket_remoteaddress">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.10</span>
</div><p>The string representation of the remote IP address. For example,
<code>'74.125.127.100'</code> or <code>'2001:4860:a005::68'</code>. Value may be <code>undefined</code> if
the socket is destroyed (for example, if the client disconnected).</p>
<h3>socket.remoteFamily<span><a class="mark" href="#net_socket_remotefamily" id="net_socket_remotefamily">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p>The string representation of the remote IP family. <code>'IPv4'</code> or <code>'IPv6'</code>.</p>
<h3>socket.remotePort<span><a class="mark" href="#net_socket_remoteport" id="net_socket_remoteport">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.10</span>
</div><p>The numeric representation of the remote port. For example,
<code>80</code> or <code>21</code>.</p>
<h3>socket.resume()<span><a class="mark" href="#net_socket_resume" id="net_socket_resume">#</a></span></h3>
<p>Resumes reading after a call to <a href="#net_socket_pause"><code>pause()</code></a>.</p>
<h3>socket.setEncoding([encoding])<span><a class="mark" href="#net_socket_setencoding_encoding" id="net_socket_setencoding_encoding">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Set the encoding for the socket as a <a href="stream.html#stream_class_stream_readable">Readable Stream</a>. See
<a href="stream.html#stream_readable_setencoding_encoding"><code>stream.setEncoding()</code></a> for more information.</p>
<h3>socket.setKeepAlive([enable][, initialDelay])<span><a class="mark" href="#net_socket_setkeepalive_enable_initialdelay" id="net_socket_setkeepalive_enable_initialdelay">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.92</span>
</div><p>Enable/disable keep-alive functionality, and optionally set the initial
delay before the first keepalive probe is sent on an idle socket.
<code>enable</code> defaults to <code>false</code>.</p>
<p>Set <code>initialDelay</code> (in milliseconds) to set the delay between the last
data packet received and the first keepalive probe. Setting 0 for
initialDelay will leave the value unchanged from the default
(or previous) setting. Defaults to <code>0</code>.</p>
<p>Returns <code>socket</code>.</p>
<h3>socket.setNoDelay([noDelay])<span><a class="mark" href="#net_socket_setnodelay_nodelay" id="net_socket_setnodelay_nodelay">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Disables the Nagle algorithm. By default TCP connections use the Nagle
algorithm, they buffer data before sending it off. Setting <code>true</code> for
<code>noDelay</code> will immediately fire off data each time <code>socket.write()</code> is called.
<code>noDelay</code> defaults to <code>true</code>.</p>
<p>Returns <code>socket</code>.</p>
<h3>socket.setTimeout(timeout[, callback])<span><a class="mark" href="#net_socket_settimeout_timeout_callback" id="net_socket_settimeout_timeout_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Sets the socket to timeout after <code>timeout</code> milliseconds of inactivity on
the socket. By default <code>net.Socket</code> do not have a timeout.</p>
<p>When an idle timeout is triggered the socket will receive a <a href="#net_event_timeout"><code>'timeout'</code></a>
event but the connection will not be severed. The user must manually <a href="#net_socket_end_data_encoding"><code>end()</code></a>
or <a href="#net_socket_destroy"><code>destroy()</code></a> the socket.</p>
<p>If <code>timeout</code> is 0, then the existing idle timeout is disabled.</p>
<p>The optional <code>callback</code> parameter will be added as a one time listener for the
<a href="#net_event_timeout"><code>'timeout'</code></a> event.</p>
<p>Returns <code>socket</code>.</p>
<h3>socket.unref()<span><a class="mark" href="#net_socket_unref" id="net_socket_unref">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>Calling <code>unref</code> on a socket will allow the program to exit if this is the only
active socket in the event system. If the socket is already <code>unref</code>d calling
<code>unref</code> again will have no effect.</p>
<p>Returns <code>socket</code>.</p>
<h3>socket.write(data[, encoding][, callback])<span><a class="mark" href="#net_socket_write_data_encoding_callback" id="net_socket_write_data_encoding_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>Sends data on the socket. The second parameter specifies the encoding in the
case of a string--it defaults to UTF8 encoding.</p>
<p>Returns <code>true</code> if the entire data was flushed successfully to the kernel
buffer. Returns <code>false</code> if all or part of the data was queued in user memory.
<a href="#stream_event_drain"><code>'drain'</code></a> will be emitted when the buffer is again free.</p>
<p>The optional <code>callback</code> parameter will be executed when the data is finally
written out - this may not be immediately.</p>
<h2>net.connect(options[, connectListener])<span><a class="mark" href="#net_net_connect_options_connectlistener" id="net_net_connect_options_connectlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p>A factory function, which returns a new <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> and automatically
connects with the supplied <code>options</code>.</p>
<p>The options are passed to both the <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> constructor and the
<a href="#net_socket_connect_options_connectlistener"><code>socket.connect</code></a> method.</p>
<p>The <code>connectListener</code> parameter will be added as a listener for the
<a href="#net_event_connect"><code>'connect'</code></a> event once.</p>
<p>Here is an example of a client of the previously described echo server:</p>
<pre><code class="lang-js">const net = require('net');
const client = net.connect({port: 8124}, () => {
// 'connect' listener
console.log('connected to server!');
client.write('world!\r\n');
});
client.on('data', (data) => {
console.log(data.toString());
client.end();
});
client.on('end', () => {
console.log('disconnected from server');
});
</code></pre>
<p>To connect on the socket <code>/tmp/echo.sock</code> the second line would just be
changed to</p>
<pre><code class="lang-js">const client = net.connect({path: '/tmp/echo.sock'});
</code></pre>
<h2>net.connect(path[, connectListener])<span><a class="mark" href="#net_net_connect_path_connectlistener" id="net_net_connect_path_connectlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>A factory function, which returns a new unix <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> and automatically
connects to the supplied <code>path</code>.</p>
<p>The <code>connectListener</code> parameter will be added as a listener for the
<a href="#net_event_connect"><code>'connect'</code></a> event once.</p>
<h2>net.connect(port[, host][, connectListener])<span><a class="mark" href="#net_net_connect_port_host_connectlistener" id="net_net_connect_port_host_connectlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>A factory function, which returns a new <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> and automatically
connects to the supplied <code>port</code> and <code>host</code>.</p>
<p>If <code>host</code> is omitted, <code>'localhost'</code> will be assumed.</p>
<p>The <code>connectListener</code> parameter will be added as a listener for the
<a href="#net_event_connect"><code>'connect'</code></a> event once.</p>
<h2>net.createConnection(options[, connectListener])<span><a class="mark" href="#net_net_createconnection_options_connectlistener" id="net_net_createconnection_options_connectlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>A factory function, which returns a new <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> and automatically
connects with the supplied <code>options</code>.</p>
<p>The options are passed to both the <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> constructor and the
<a href="#net_socket_connect_options_connectlistener"><code>socket.connect</code></a> method.</p>
<p>The <code>connectListener</code> parameter will be added as a listener for the
<a href="#net_event_connect"><code>'connect'</code></a> event once.</p>
<p>Here is an example of a client of the previously described echo server:</p>
<pre><code class="lang-js">const net = require('net');
const client = net.createConnection({port: 8124}, () => {
//'connect' listener
console.log('connected to server!');
client.write('world!\r\n');
});
client.on('data', (data) => {
console.log(data.toString());
client.end();
});
client.on('end', () => {
console.log('disconnected from server');
});
</code></pre>
<p>To connect on the socket <code>/tmp/echo.sock</code> the second line would just be
changed to</p>
<pre><code class="lang-js">const client = net.connect({path: '/tmp/echo.sock'});
</code></pre>
<h2>net.createConnection(path[, connectListener])<span><a class="mark" href="#net_net_createconnection_path_connectlistener" id="net_net_createconnection_path_connectlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>A factory function, which returns a new unix <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> and automatically
connects to the supplied <code>path</code>.</p>
<p>The <code>connectListener</code> parameter will be added as a listener for the
<a href="#net_event_connect"><code>'connect'</code></a> event once.</p>
<h2>net.createConnection(port[, host][, connectListener])<span><a class="mark" href="#net_net_createconnection_port_host_connectlistener" id="net_net_createconnection_port_host_connectlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.90</span>
</div><p>A factory function, which returns a new <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> and automatically
connects to the supplied <code>port</code> and <code>host</code>.</p>
<p>If <code>host</code> is omitted, <code>'localhost'</code> will be assumed.</p>
<p>The <code>connectListener</code> parameter will be added as a listener for the
<a href="#net_event_connect"><code>'connect'</code></a> event once.</p>
<h2>net.createServer([options][, connectionListener])<span><a class="mark" href="#net_net_createserver_options_connectionlistener" id="net_net_createserver_options_connectionlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Creates a new server. The <code>connectionListener</code> argument is
automatically set as a listener for the <a href="#net_event_connection"><code>'connection'</code></a> event.</p>
<p><code>options</code> is an object with the following defaults:</p>
<pre><code class="lang-js">{
allowHalfOpen: false,
pauseOnConnect: false
}
</code></pre>
<p>If <code>allowHalfOpen</code> is <code>true</code>, then the socket won't automatically send a FIN
packet when the other end of the socket sends a FIN packet. The socket becomes
non-readable, but still writable. You should call the <a href="#net_socket_end_data_encoding"><code>end()</code></a> method explicitly.
See <a href="#stream_event_end"><code>'end'</code></a> event for more information.</p>
<p>If <code>pauseOnConnect</code> is <code>true</code>, then the socket associated with each incoming
connection will be paused, and no data will be read from its handle. This allows
connections to be passed between processes without any data being read by the
original process. To begin reading data from a paused socket, call <a href="#net_socket_resume"><code>resume()</code></a>.</p>
<p>Here is an example of an echo server which listens for connections
on port 8124:</p>
<pre><code class="lang-js">const net = require('net');
const server = net.createServer((c) => {
// 'connection' listener
console.log('client connected');
c.on('end', () => {
console.log('client disconnected');
});
c.write('hello\r\n');
c.pipe(c);
});
server.on('error', (err) => {
throw err;
});
server.listen(8124, () => {
console.log('server bound');
});
</code></pre>
<p>Test this by using <code>telnet</code>:</p>
<pre><code>telnet localhost 8124
</code></pre><p>To listen on the socket <code>/tmp/echo.sock</code> the third line from the last would
just be changed to</p>
<pre><code class="lang-js">server.listen('/tmp/echo.sock', () => {
console.log('server bound');
});
</code></pre>
<p>Use <code>nc</code> to connect to a UNIX domain socket server:</p>
<pre><code class="lang-js">nc -U /tmp/echo.sock
</code></pre>
<h2>net.isIP(input)<span><a class="mark" href="#net_net_isip_input" id="net_net_isip_input">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>Tests if input is an IP address. Returns 0 for invalid strings,
returns 4 for IP version 4 addresses, and returns 6 for IP version 6 addresses.</p>
<h2>net.isIPv4(input)<span><a class="mark" href="#net_net_isipv4_input" id="net_net_isipv4_input">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>Returns true if input is a version 4 IP address, otherwise returns false.</p>
<h2>net.isIPv6(input)<span><a class="mark" href="#net_net_isipv6_input" id="net_net_isipv6_input">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>Returns true if input is a version 6 IP address, otherwise returns false.</p>
<!-- [end-include:net.md] -->
<!-- [start-include:os.md] -->
<h1>OS<span><a class="mark" href="#os_os" id="os_os">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>Provides a few basic operating-system related utility functions.</p>
<p>Use <code>require('os')</code> to access this module.</p>
<h2>os.EOL<span><a class="mark" href="#os_os_eol" id="os_os_eol">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.8</span>
</div><p>A constant defining the appropriate End-of-line marker for the operating
system.</p>
<h2>os.arch()<span><a class="mark" href="#os_os_arch" id="os_os_arch">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Returns the operating system CPU architecture. Possible values are <code>'x64'</code>,
<code>'arm'</code> and <code>'ia32'</code>. Returns the value of <a href="process.html#process_process_arch"><code>process.arch</code></a>.</p>
<h2>os.cpus()<span><a class="mark" href="#os_os_cpus" id="os_os_cpus">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Returns an array of objects containing information about each CPU/core
installed: model, speed (in MHz), and times (an object containing the number of
milliseconds the CPU/core spent in: user, nice, sys, idle, and irq).</p>
<p>Example inspection of os.cpus:</p>
<pre><code class="lang-js">[ { model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 252020,
nice: 0,
sys: 30340,
idle: 1070356870,
irq: 0 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 306960,
nice: 0,
sys: 26980,
idle: 1071569080,
irq: 0 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 248450,
nice: 0,
sys: 21750,
idle: 1070919370,
irq: 0 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 256880,
nice: 0,
sys: 19430,
idle: 1070905480,
irq: 20 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 511580,
nice: 20,
sys: 40900,
idle: 1070842510,
irq: 0 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 291660,
nice: 0,
sys: 34360,
idle: 1070888000,
irq: 10 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 308260,
nice: 0,
sys: 55410,
idle: 1071129970,
irq: 880 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 266450,
nice: 1480,
sys: 34920,
idle: 1072572010,
irq: 30 } } ]
</code></pre>
<p>Note that since <code>nice</code> values are UNIX centric in Windows the <code>nice</code> values of
all processors are always 0.</p>
<h2>os.endianness()<span><a class="mark" href="#os_os_endianness" id="os_os_endianness">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.4</span>
</div><p>Returns the endianness of the CPU. Possible values are <code>'BE'</code> for big endian
or <code>'LE'</code> for little endian.</p>
<h2>os.freemem()<span><a class="mark" href="#os_os_freemem" id="os_os_freemem">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Returns the amount of free system memory in bytes.</p>
<h2>os.homedir()<span><a class="mark" href="#os_os_homedir" id="os_os_homedir">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v2.3.0</span>
</div><p>Returns the home directory of the current user.</p>
<h2>os.hostname()<span><a class="mark" href="#os_os_hostname" id="os_os_hostname">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Returns the hostname of the operating system.</p>
<h2>os.loadavg()<span><a class="mark" href="#os_os_loadavg" id="os_os_loadavg">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Returns an array containing the 1, 5, and 15 minute load averages.</p>
<p>The load average is a measure of system activity, calculated by the operating
system and expressed as a fractional number. As a rule of thumb, the load
average should ideally be less than the number of logical CPUs in the system.</p>
<p>The load average is a very UNIX-y concept; there is no real equivalent on
Windows platforms. That is why this function always returns <code>[0, 0, 0]</code> on
Windows.</p>
<h2>os.networkInterfaces()<span><a class="mark" href="#os_os_networkinterfaces" id="os_os_networkinterfaces">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><p>Get a list of network interfaces:</p>
<pre><code class="lang-js">{ lo:
[ { address: '127.0.0.1',
netmask: '255.0.0.0',
family: 'IPv4',
mac: '00:00:00:00:00:00',
internal: true },
{ address: '::1',
netmask: 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff',
family: 'IPv6',
mac: '00:00:00:00:00:00',
internal: true } ],
eth0:
[ { address: '192.168.1.108',
netmask: '255.255.255.0',
family: 'IPv4',
mac: '01:02:03:0a:0b:0c',
internal: false },
{ address: 'fe80::a00:27ff:fe4e:66a1',
netmask: 'ffff:ffff:ffff:ffff::',
family: 'IPv6',
mac: '01:02:03:0a:0b:0c',
internal: false } ] }
</code></pre>
<p>Note that due to the underlying implementation this will only return network
interfaces that have been assigned an address.</p>
<h2>os.platform()<span><a class="mark" href="#os_os_platform" id="os_os_platform">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Returns the operating system platform. Possible values are <code>'darwin'</code>,
<code>'freebsd'</code>, <code>'linux'</code>, <code>'sunos'</code> or <code>'win32'</code>. Returns the value of
<a href="process.html#process_process_platform"><code>process.platform</code></a>.</p>
<h2>os.release()<span><a class="mark" href="#os_os_release" id="os_os_release">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Returns the operating system release.</p>
<h2>os.tmpdir()<span><a class="mark" href="#os_os_tmpdir" id="os_os_tmpdir">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.9</span>
</div><p>Returns the operating system's default directory for temporary files.</p>
<h2>os.totalmem()<span><a class="mark" href="#os_os_totalmem" id="os_os_totalmem">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Returns the total amount of system memory in bytes.</p>
<h2>os.type()<span><a class="mark" href="#os_os_type" id="os_os_type">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Returns the operating system name. For example <code>'Linux'</code> on Linux, <code>'Darwin'</code>
on OS X and <code>'Windows_NT'</code> on Windows.</p>
<h2>os.uptime()<span><a class="mark" href="#os_os_uptime" id="os_os_uptime">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Returns the system uptime in seconds.</p>
<!-- [end-include:os.md] -->
<!-- [start-include:path.md] -->
<h1>Path<span><a class="mark" href="#path_path" id="path_path">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>This module contains utilities for handling and transforming file
paths. Almost all these methods perform only string transformations.
The file system is not consulted to check whether paths are valid.</p>
<p>Use <code>require('path')</code> to use this module. The following methods are provided:</p>
<h2>path.basename(p[, ext])<span><a class="mark" href="#path_path_basename_p_ext" id="path_path_basename_p_ext">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>Return the last portion of a path. Similar to the Unix <code>basename</code> command.</p>
<p>Example:</p>
<pre><code class="lang-js">path.basename('/foo/bar/baz/asdf/quux.html')
// returns 'quux.html'
path.basename('/foo/bar/baz/asdf/quux.html', '.html')
// returns 'quux'
</code></pre>
<h2>path.delimiter<span><a class="mark" href="#path_path_delimiter" id="path_path_delimiter">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.3</span>
</div><p>The platform-specific path delimiter, <code>;</code> or <code>':'</code>.</p>
<p>An example on *nix:</p>
<pre><code class="lang-js">console.log(process.env.PATH)
// '/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin'
process.env.PATH.split(path.delimiter)
// returns ['/usr/bin', '/bin', '/usr/sbin', '/sbin', '/usr/local/bin']
</code></pre>
<p>An example on Windows:</p>
<pre><code class="lang-js">console.log(process.env.PATH)
// 'C:\Windows\system32;C:\Windows;C:\Program Files\node\'
process.env.PATH.split(path.delimiter)
// returns ['C:\\Windows\\system32', 'C:\\Windows', 'C:\\Program Files\\node\\']
</code></pre>
<h2>path.dirname(p)<span><a class="mark" href="#path_path_dirname_p" id="path_path_dirname_p">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><p>Return the directory name of a path. Similar to the Unix <code>dirname</code> command.</p>
<p>Example:</p>
<pre><code class="lang-js">path.dirname('/foo/bar/baz/asdf/quux')
// returns '/foo/bar/baz/asdf'
</code></pre>
<h2>path.extname(p)<span><a class="mark" href="#path_path_extname_p" id="path_path_extname_p">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>Return the extension of the path, from the last '.' to end of string
in the last portion of the path. If there is no '.' in the last portion
of the path or the first character of it is '.', then it returns
an empty string. Examples:</p>
<pre><code class="lang-js">path.extname('index.html')
// returns '.html'
path.extname('index.coffee.md')
// returns '.md'
path.extname('index.')
// returns '.'
path.extname('index')
// returns ''
path.extname('.index')
// returns ''
</code></pre>
<h2>path.format(pathObject)<span><a class="mark" href="#path_path_format_pathobject" id="path_path_format_pathobject">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.15</span>
</div><p>Returns a path string from an object, the opposite of <a href="#path_path_parse_pathstring"><code>path.parse</code></a>.</p>
<p>Examples:</p>
<p>Some Posix system examples:</p>
<pre><code class="lang-js">// If `dir` and `base` are provided, `dir` + platform separator + `base`
// will be returned.
path.format({
dir: '/home/user/dir',
base: 'file.txt'
});
// returns '/home/user/dir/file.txt'
// `base` will be returned if `dir` or `root` are not provided.
path.format({
base: 'file.txt'
});
// returns 'file.txt'
</code></pre>
<h2>path.isAbsolute(path)<span><a class="mark" href="#path_path_isabsolute_path" id="path_path_isabsolute_path">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.2</span>
</div><p>Determines whether <code>path</code> is an absolute path. An absolute path will always
resolve to the same location, regardless of the working directory.</p>
<p>Posix examples:</p>
<pre><code class="lang-js">path.isAbsolute('/foo/bar') // true
path.isAbsolute('/baz/..') // true
path.isAbsolute('qux/') // false
path.isAbsolute('.') // false
</code></pre>
<p>Windows examples:</p>
<pre><code class="lang-js">path.isAbsolute('//server') // true
path.isAbsolute('C:/foo/..') // true
path.isAbsolute('bar\\baz') // false
path.isAbsolute('.') // false
</code></pre>
<p><em>Note:</em> If the path string passed as parameter is a zero-length string, unlike
other path module functions, it will be used as-is and <code>false</code> will be
returned.</p>
<h2>path.join([path1][, path2][, ...])<span><a class="mark" href="#path_path_join_path1_path2" id="path_path_join_path1_path2">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><p>Join all arguments together and normalize the resulting path.</p>
<p>Arguments must be strings. In v0.8, non-string arguments were
silently ignored. In v0.10 and up, an exception is thrown.</p>
<p>Example:</p>
<pre><code class="lang-js">path.join('/foo', 'bar', 'baz/asdf', 'quux', '..')
// returns '/foo/bar/baz/asdf'
path.join('foo', {}, 'bar')
// throws exception
TypeError: Arguments to path.join must be strings
</code></pre>
<p><em>Note:</em> If the arguments to <code>join</code> have zero-length strings, unlike other path
module functions, they will be ignored. If the joined path string is a
zero-length string then <code>'.'</code> will be returned, which represents the
current working directory.</p>
<h2>path.normalize(p)<span><a class="mark" href="#path_path_normalize_p" id="path_path_normalize_p">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.23</span>
</div><p>Normalize a string path, taking care of <code>'..'</code> and <code>'.'</code> parts.</p>
<p>When multiple slashes are found, they're replaced by a single one;
when the path contains a trailing slash, it is preserved.
On Windows backslashes are used.</p>
<p>Example:</p>
<pre><code class="lang-js">path.normalize('/foo/bar//baz/asdf/quux/..')
// returns '/foo/bar/baz/asdf'
</code></pre>
<p><em>Note:</em> If the path string passed as argument is a zero-length string then <code>'.'</code>
will be returned, which represents the current working directory.</p>
<h2>path.parse(pathString)<span><a class="mark" href="#path_path_parse_pathstring" id="path_path_parse_pathstring">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.15</span>
</div><p>Returns an object from a path string.</p>
<p>An example on *nix:</p>
<pre><code class="lang-js">path.parse('/home/user/dir/file.txt')
// returns
// {
// root : "/",
// dir : "/home/user/dir",
// base : "file.txt",
// ext : ".txt",
// name : "file"
// }
</code></pre>
<p>An example on Windows:</p>
<pre><code class="lang-js">path.parse('C:\\path\\dir\\index.html')
// returns
// {
// root : "C:\\",
// dir : "C:\\path\\dir",
// base : "index.html",
// ext : ".html",
// name : "index"
// }
</code></pre>
<h2>path.posix<span><a class="mark" href="#path_path_posix" id="path_path_posix">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.15</span>
</div><p>Provide access to aforementioned <code>path</code> methods but always interact in a posix
compatible way.</p>
<h2>path.relative(from, to)<span><a class="mark" href="#path_path_relative_from_to" id="path_path_relative_from_to">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Solve the relative path from <code>from</code> to <code>to</code>.</p>
<p>At times we have two absolute paths, and we need to derive the relative
path from one to the other. This is actually the reverse transform of
<code>path.resolve</code>, which means we see that:</p>
<pre><code class="lang-js">path.resolve(from, path.relative(from, to)) == path.resolve(to)
</code></pre>
<p>Examples:</p>
<pre><code class="lang-js">path.relative('C:\\orandea\\test\\aaa', 'C:\\orandea\\impl\\bbb')
// returns '..\\..\\impl\\bbb'
path.relative('/data/orandea/test/aaa', '/data/orandea/impl/bbb')
// returns '../../impl/bbb'
</code></pre>
<p><em>Note:</em> If the arguments to <code>relative</code> have zero-length strings then the current
working directory will be used instead of the zero-length strings. If
both the paths are the same then a zero-length string will be returned.</p>
<h2>path.resolve([from ...], to)<span><a class="mark" href="#path_path_resolve_from_to" id="path_path_resolve_from_to">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><p>Resolves <code>to</code> to an absolute path.</p>
<p>If <code>to</code> isn't already absolute <code>from</code> arguments are prepended in right to left
order, until an absolute path is found. If after using all <code>from</code> paths still
no absolute path is found, the current working directory is used as well. The
resulting path is normalized, and trailing slashes are removed unless the path
gets resolved to the root directory. Non-string <code>from</code> arguments are ignored.</p>
<p>Another way to think of it is as a sequence of <code>cd</code> commands in a shell.</p>
<pre><code class="lang-js">path.resolve('foo/bar', '/tmp/file/', '..', 'a/../subfile')
</code></pre>
<p>Is similar to:</p>
<pre><code>cd foo/bar
cd /tmp/file/
cd ..
cd a/../subfile
pwd
</code></pre><p>The difference is that the different paths don't need to exist and may also be
files.</p>
<p>Examples:</p>
<pre><code class="lang-js">path.resolve('/foo/bar', './baz')
// returns '/foo/bar/baz'
path.resolve('/foo/bar', '/tmp/file/')
// returns '/tmp/file'
path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif')
// if currently in /home/myself/node, it returns
// '/home/myself/node/wwwroot/static_files/gif/image.gif'
</code></pre>
<p><em>Note:</em> If the arguments to <code>resolve</code> have zero-length strings then the current
working directory will be used instead of them.</p>
<h2>path.sep<span><a class="mark" href="#path_path_sep" id="path_path_sep">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.9</span>
</div><p>The platform-specific file separator. <code>'\\'</code> or <code>'/'</code>.</p>
<p>An example on *nix:</p>
<pre><code class="lang-js">'foo/bar/baz'.split(path.sep)
// returns ['foo', 'bar', 'baz']
</code></pre>
<p>An example on Windows:</p>
<pre><code class="lang-js">'foo\\bar\\baz'.split(path.sep)
// returns ['foo', 'bar', 'baz']
</code></pre>
<h2>path.win32<span><a class="mark" href="#path_path_win32" id="path_path_win32">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.15</span>
</div><p>Provide access to aforementioned <code>path</code> methods but always interact in a win32
compatible way.</p>
<!-- [end-include:path.md] -->
<!-- [start-include:process.md] -->
<h1>Process<span><a class="mark" href="#process_process" id="process_process">#</a></span></h1>
<!-- type=global -->
<p>The <code>process</code> object is a global object and can be accessed from anywhere.
It is an instance of <a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a>.</p>
<h2>Event: 'beforeExit'<span><a class="mark" href="#process_event_beforeexit" id="process_event_beforeexit">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>This event is emitted when Node.js empties its event loop and has nothing else
to schedule. Normally, Node.js exits when there is no work scheduled, but a
listener for <code>'beforeExit'</code> can make asynchronous calls, and cause Node.js to
continue.</p>
<p><code>'beforeExit'</code> is not emitted for conditions causing explicit termination, such
as <a href="#process_process_exit_code"><code>process.exit()</code></a> or uncaught exceptions, and should not be used as an
alternative to the <code>'exit'</code> event unless the intention is to schedule more work.</p>
<h2>Event: 'exit'<span><a class="mark" href="#process_event_exit" id="process_event_exit">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.7</span>
</div><p>Emitted when the process is about to exit. There is no way to prevent the
exiting of the event loop at this point, and once all <code>'exit'</code> listeners have
finished running the process will exit. Therefore you <strong>must</strong> only perform
<strong>synchronous</strong> operations in this handler. This is a good hook to perform
checks on the module's state (like for unit tests). The callback takes one
argument, the code the process is exiting with.</p>
<p>This event is only emitted when Node.js exits explicitly by process.exit() or
implicitly by the event loop draining.</p>
<p>Example of listening for <code>'exit'</code>:</p>
<pre><code class="lang-js">process.on('exit', (code) => {
// do *NOT* do this
setTimeout(() => {
console.log('This will not run');
}, 0);
console.log('About to exit with code:', code);
});
</code></pre>
<h2>Event: 'message'<span><a class="mark" href="#process_event_message" id="process_event_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.10</span>
</div><ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> a parsed JSON object or primitive value</li>
<li><code>sendHandle</code> <span class="type"><Handle object></span> a <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> or <a href="net.html#net_class_net_server"><code>net.Server</code></a> object, or
undefined.</li>
</ul>
<p>Messages sent by <a href="child_process.html#child_process_child_send_message_sendhandle_callback"><code>ChildProcess.send()</code></a> are obtained using the <code>'message'</code>
event on the child's process object.</p>
<h2>Event: 'rejectionHandled'<span><a class="mark" href="#process_event_rejectionhandled" id="process_event_rejectionhandled">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v1.4.1</span>
</div><p>Emitted whenever a Promise was rejected and an error handler was attached to it
(for example with <code>.catch()</code>) later than after an event loop turn. This event
is emitted with the following arguments:</p>
<ul>
<li><code>p</code> the promise that was previously emitted in an <code>'unhandledRejection'</code>
event, but which has now gained a rejection handler.</li>
</ul>
<p>There is no notion of a top level for a promise chain at which rejections can
always be handled. Being inherently asynchronous in nature, a promise rejection
can be handled at a future point in time — possibly much later than the
event loop turn it takes for the <code>'unhandledRejection'</code> event to be emitted.</p>
<p>Another way of stating this is that, unlike in synchronous code where there is
an ever-growing list of unhandled exceptions, with promises there is a
growing-and-shrinking list of unhandled rejections. In synchronous code, the
<code>'uncaughtException'</code> event tells you when the list of unhandled exceptions
grows. And in asynchronous code, the <code>'unhandledRejection'</code> event tells you
when the list of unhandled rejections grows, while the <code>'rejectionHandled'</code>
event tells you when the list of unhandled rejections shrinks.</p>
<p>For example using the rejection detection hooks in order to keep a map of all
the rejected promise reasons at a given time:</p>
<pre><code class="lang-js">const unhandledRejections = new Map();
process.on('unhandledRejection', (reason, p) => {
unhandledRejections.set(p, reason);
});
process.on('rejectionHandled', (p) => {
unhandledRejections.delete(p);
});
</code></pre>
<p>This map will grow and shrink over time, reflecting rejections that start
unhandled and then become handled. You could record the errors in some error
log, either periodically (probably best for long-running programs, allowing
you to clear the map, which in the case of a very buggy program could grow
indefinitely) or upon process exit (more convenient for scripts).</p>
<h2>Event: 'uncaughtException'<span><a class="mark" href="#process_event_uncaughtexception" id="process_event_uncaughtexception">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.18</span>
</div><p>The <code>'uncaughtException'</code> event is emitted when an exception bubbles all the
way back to the event loop. By default, Node.js handles such exceptions by
printing the stack trace to stderr and exiting. Adding a handler for the
<code>'uncaughtException'</code> event overrides this default behavior.</p>
<p>For example:</p>
<pre><code class="lang-js">process.on('uncaughtException', (err) => {
console.log(`Caught exception: ${err}`);
});
setTimeout(() => {
console.log('This will still run.');
}, 500);
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');
</code></pre>
<h3>Warning: Using <code>'uncaughtException'</code> correctly<span><a class="mark" href="#process_warning_using_uncaughtexception_correctly" id="process_warning_using_uncaughtexception_correctly">#</a></span></h3>
<p>Note that <code>'uncaughtException'</code> is a crude mechanism for exception handling
intended to be used only as a last resort. The event <em>should not</em> be used as
an equivalent to <code>On Error Resume Next</code>. Unhandled exceptions inherently mean
that an application is in an undefined state. Attempting to resume application
code without properly recovering from the exception can cause additional
unforeseen and unpredictable issues.</p>
<p>Exceptions thrown from within the event handler will not be caught. Instead the
process will exit with a non-zero exit code and the stack trace will be printed.
This is to avoid infinite recursion.</p>
<p>Attempting to resume normally after an uncaught exception can be similar to
pulling out of the power cord when upgrading a computer -- nine out of ten
times nothing happens - but the 10th time, the system becomes corrupted.</p>
<p>The correct use of <code>'uncaughtException'</code> is to perform synchronous cleanup
of allocated resources (e.g. file descriptors, handles, etc) before shutting
down the process. It is not safe to resume normal operation after
<code>'uncaughtException'</code>.</p>
<h2>Event: 'unhandledRejection'<span><a class="mark" href="#process_event_unhandledrejection" id="process_event_unhandledrejection">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v1.4.1</span>
</div><p>Emitted whenever a <code>Promise</code> is rejected and no error handler is attached to
the promise within a turn of the event loop. When programming with promises
exceptions are encapsulated as rejected promises. Such promises can be caught
and handled using <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/catch"><code>promise.catch(...)</code></a> and rejections are propagated through
a promise chain. This event is useful for detecting and keeping track of
promises that were rejected whose rejections were not handled yet. This event
is emitted with the following arguments:</p>
<ul>
<li><code>reason</code> the object with which the promise was rejected (usually an
<a href="errors.html#errors_class_error"><code>Error</code></a> instance).</li>
<li><code>p</code> the promise that was rejected.</li>
</ul>
<p>Here is an example that logs every unhandled rejection to the console</p>
<pre><code class="lang-js">process.on('unhandledRejection', (reason, p) => {
console.log('Unhandled Rejection at: Promise', p, 'reason:', reason);
// application specific logging, throwing an error, or other logic here
});
</code></pre>
<p>For example, here is a rejection that will trigger the <code>'unhandledRejection'</code>
event:</p>
<pre><code class="lang-js">somePromise.then((res) => {
return reportToUser(JSON.pasre(res)); // note the typo (`pasre`)
}); // no `.catch` or `.then`
</code></pre>
<p>Here is an example of a coding pattern that will also trigger
<code>'unhandledRejection'</code>:</p>
<pre><code class="lang-js">function SomeResource() {
// Initially set the loaded status to a rejected promise
this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}
var resource = new SomeResource();
// no .catch or .then on resource.loaded for at least a turn
</code></pre>
<p>In cases like this, you may not want to track the rejection as a developer
error like you would for other <code>'unhandledRejection'</code> events. To address
this, you can either attach a dummy <code>.catch(() => { })</code> handler to
<code>resource.loaded</code>, preventing the <code>'unhandledRejection'</code> event from being
emitted, or you can use the <a href="#process_event_rejectionhandled"><code>'rejectionHandled'</code></a> event.</p>
<h2>Exit Codes<span><a class="mark" href="#process_exit_codes" id="process_exit_codes">#</a></span></h2>
<p>Node.js will normally exit with a <code>0</code> status code when no more async
operations are pending. The following status codes are used in other
cases:</p>
<ul>
<li><code>1</code> <strong>Uncaught Fatal Exception</strong> - There was an uncaught exception,
and it was not handled by a domain or an <code>'uncaughtException'</code> event
handler.</li>
<li><code>2</code> - Unused (reserved by Bash for builtin misuse)</li>
<li><code>3</code> <strong>Internal JavaScript Parse Error</strong> - The JavaScript source code
internal in Node.js's bootstrapping process caused a parse error. This
is extremely rare, and generally can only happen during development
of Node.js itself.</li>
<li><code>4</code> <strong>Internal JavaScript Evaluation Failure</strong> - The JavaScript
source code internal in Node.js's bootstrapping process failed to
return a function value when evaluated. This is extremely rare, and
generally can only happen during development of Node.js itself.</li>
<li><code>5</code> <strong>Fatal Error</strong> - There was a fatal unrecoverable error in V8.
Typically a message will be printed to stderr with the prefix <code>FATAL
ERROR</code>.</li>
<li><code>6</code> <strong>Non-function Internal Exception Handler</strong> - There was an
uncaught exception, but the internal fatal exception handler
function was somehow set to a non-function, and could not be called.</li>
<li><code>7</code> <strong>Internal Exception Handler Run-Time Failure</strong> - There was an
uncaught exception, and the internal fatal exception handler
function itself threw an error while attempting to handle it. This
can happen, for example, if a <code>process.on('uncaughtException')</code> or
<code>domain.on('error')</code> handler throws an error.</li>
<li><code>8</code> - Unused. In previous versions of Node.js, exit code 8 sometimes
indicated an uncaught exception.</li>
<li><code>9</code> - <strong>Invalid Argument</strong> - Either an unknown option was specified,
or an option requiring a value was provided without a value.</li>
<li><code>10</code> <strong>Internal JavaScript Run-Time Failure</strong> - The JavaScript
source code internal in Node.js's bootstrapping process threw an error
when the bootstrapping function was called. This is extremely rare,
and generally can only happen during development of Node.js itself.</li>
<li><code>12</code> <strong>Invalid Debug Argument</strong> - The <code>--debug</code> and/or <code>--debug-brk</code>
options were set, but an invalid port number was chosen.</li>
<li><code>>128</code> <strong>Signal Exits</strong> - If Node.js receives a fatal signal such as
<code>SIGKILL</code> or <code>SIGHUP</code>, then its exit code will be <code>128</code> plus the
value of the signal code. This is a standard Unix practice, since
exit codes are defined to be 7-bit integers, and signal exits set
the high-order bit, and then contain the value of the signal code.</li>
</ul>
<h2>Signal Events<span><a class="mark" href="#process_signal_events" id="process_signal_events">#</a></span></h2>
<!--type=event-->
<!--name=SIGINT, SIGHUP, etc.-->
<p>Emitted when the processes receives a signal. See <a href="http://man7.org/linux/man-pages/man7/sigaction.7.html">sigaction(7)</a> for a list of
standard POSIX signal names such as <code>SIGINT</code>, <code>SIGHUP</code>, etc.</p>
<p>Example of listening for <code>SIGINT</code>:</p>
<pre><code class="lang-js">// Start reading from stdin so we don't exit.
process.stdin.resume();
process.on('SIGINT', () => {
console.log('Got SIGINT. Press Control-D to exit.');
});
</code></pre>
<p>An easy way to send the <code>SIGINT</code> signal is with <code>Control-C</code> in most terminal
programs.</p>
<p>Note:</p>
<ul>
<li><code>SIGUSR1</code> is reserved by Node.js to start the debugger. It's possible to
install a listener but that won't stop the debugger from starting.</li>
<li><code>SIGTERM</code> and <code>SIGINT</code> have default handlers on non-Windows platforms that
resets the terminal mode before exiting with code <code>128 + signal number</code>. If
one of these signals has a listener installed, its default behavior will be
removed (Node.js will no longer exit).</li>
<li><code>SIGPIPE</code> is ignored by default. It can have a listener installed.</li>
<li><code>SIGHUP</code> is generated on Windows when the console window is closed, and on other
platforms under various similar conditions, see <a href="http://man7.org/linux/man-pages/man7/signal.7.html">signal(7)</a>. It can have a
listener installed, however Node.js will be unconditionally terminated by
Windows about 10 seconds later. On non-Windows platforms, the default
behavior of <code>SIGHUP</code> is to terminate Node.js, but once a listener has been
installed its default behavior will be removed.</li>
<li><code>SIGTERM</code> is not supported on Windows, it can be listened on.</li>
<li><code>SIGINT</code> from the terminal is supported on all platforms, and can usually be
generated with <code>CTRL+C</code> (though this may be configurable). It is not generated
when terminal raw mode is enabled.</li>
<li><code>SIGBREAK</code> is delivered on Windows when <code>CTRL+BREAK</code> is pressed, on
non-Windows
platforms it can be listened on, but there is no way to send or generate it.</li>
<li><code>SIGWINCH</code> is delivered when the console has been resized. On Windows, this
will only happen on write to the console when the cursor is being moved, or
when a readable tty is used in raw mode.</li>
<li><code>SIGKILL</code> cannot have a listener installed, it will unconditionally terminate
Node.js on all platforms.</li>
<li><code>SIGSTOP</code> cannot have a listener installed.</li>
</ul>
<p>Note that Windows does not support sending Signals, but Node.js offers some
emulation with <code>process.kill()</code>, and <code>child_process.kill()</code>. Sending signal <code>0</code>
can be used to test for the existence of a process. Sending <code>SIGINT</code>,
<code>SIGTERM</code>, and <code>SIGKILL</code> cause the unconditional termination of the target
process.</p>
<h2>process.abort()<span><a class="mark" href="#process_process_abort" id="process_process_abort">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p>This causes Node.js to emit an abort. This will cause Node.js to exit and
generate a core file.</p>
<h2>process.arch<span><a class="mark" href="#process_process_arch" id="process_process_arch">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>What processor architecture you're running on: <code>'arm'</code>, <code>'ia32'</code>, or <code>'x64'</code>.</p>
<pre><code class="lang-js">console.log('This processor architecture is ' + process.arch);
</code></pre>
<h2>process.argv<span><a class="mark" href="#process_process_argv" id="process_process_argv">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.27</span>
</div><p>An array containing the command line arguments. The first element will be
'node', the second element will be the name of the JavaScript file. The
next elements will be any additional command line arguments.</p>
<pre><code class="lang-js">// print process.argv
process.argv.forEach((val, index, array) => {
console.log(`${index}: ${val}`);
});
</code></pre>
<p>This will generate:</p>
<pre><code>$ node process-2.js one two=three four
0: node
1: /Users/mjr/work/node/process-2.js
2: one
3: two=three
4: four
</code></pre><h2>process.chdir(directory)<span><a class="mark" href="#process_process_chdir_directory" id="process_process_chdir_directory">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.17</span>
</div><p>Changes the current working directory of the process or throws an exception if that fails.</p>
<pre><code class="lang-js">console.log(`Starting directory: ${process.cwd()}`);
try {
process.chdir('/tmp');
console.log(`New directory: ${process.cwd()}`);
}
catch (err) {
console.log(`chdir: ${err}`);
}
</code></pre>
<h2>process.config<span><a class="mark" href="#process_process_config" id="process_process_config">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>An Object containing the JavaScript representation of the configure options
that were used to compile the current Node.js executable. This is the same as
the <code>config.gypi</code> file that was produced when running the <code>./configure</code> script.</p>
<p>An example of the possible output looks like:</p>
<pre><code>{
target_defaults:
{ cflags: [],
default_configuration: 'Release',
defines: [],
include_dirs: [],
libraries: [] },
variables:
{
host_arch: 'x64',
node_install_npm: 'true',
node_prefix: '',
node_shared_cares: 'false',
node_shared_http_parser: 'false',
node_shared_libuv: 'false',
node_shared_zlib: 'false',
node_use_dtrace: 'false',
node_use_openssl: 'true',
node_shared_openssl: 'false',
strict_aliasing: 'true',
target_arch: 'x64',
v8_use_snapshot: 'true'
}
}
</code></pre><p><em>Note: the <code>process.config</code> property is <strong>not</strong> read-only and there are existing
modules in the ecosystem that are known to extend, modify, or entirely replace
the value of <code>process.config</code>.</em></p>
<h2>process.connected<span><a class="mark" href="#process_process_connected" id="process_process_connected">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.2</span>
</div><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Set to false after <code>process.disconnect()</code> is called</li>
</ul>
<p>If <code>process.connected</code> is false, it is no longer possible to send messages.</p>
<h2>process.cpuUsage([previousValue])<span><a class="mark" href="#process_process_cpuusage_previousvalue" id="process_process_cpuusage_previousvalue">#</a></span></h2>
<p>Returns the user and system CPU time usage of the current process, in an object
with properties <code>user</code> and <code>system</code>, whose values are microsecond values
(millionth of a second). These values measure time spent in user and
system code respectively, and may end up being greater than actual elapsed time
if multiple CPU cores are performing work for this process.</p>
<p>The result of a previous call to <code>process.cpuUsage()</code> can be passed as the
argument to the function, to get a diff reading.</p>
<pre><code class="lang-js">const startUsage = process.cpuUsage();
// { user: 38579, system: 6986 }
// spin the CPU for 500 milliseconds
const now = Date.now();
while (Date.now() - now < 500);
console.log(process.cpuUsage(startUsage));
// { user: 514883, system: 11226 }
</code></pre>
<h2>process.cwd()<span><a class="mark" href="#process_process_cwd" id="process_process_cwd">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.8</span>
</div><p>Returns the current working directory of the process.</p>
<pre><code class="lang-js">console.log(`Current directory: ${process.cwd()}`);
</code></pre>
<h2>process.disconnect()<span><a class="mark" href="#process_process_disconnect" id="process_process_disconnect">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.2</span>
</div><p>Close the IPC channel to the parent process, allowing this child to exit
gracefully once there are no other connections keeping it alive.</p>
<p>Identical to the parent process's <a href="child_process.html#child_process_child_disconnect"><code>ChildProcess.disconnect()</code></a>.</p>
<p>If Node.js was not spawned with an IPC channel, <code>process.disconnect()</code> will be
undefined.</p>
<h2>process.env<span><a class="mark" href="#process_process_env" id="process_process_env">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.27</span>
</div><p>An object containing the user environment. See <a href="http://man7.org/linux/man-pages/man7/environ.7.html">environ(7)</a>.</p>
<p>An example of this object looks like:</p>
<pre><code class="lang-js">{ TERM: 'xterm-256color',
SHELL: '/usr/local/bin/bash',
USER: 'maciej',
PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
PWD: '/Users/maciej',
EDITOR: 'vim',
SHLVL: '1',
HOME: '/Users/maciej',
LOGNAME: 'maciej',
_: '/usr/local/bin/node' }
</code></pre>
<p>You can write to this object, but changes won't be reflected outside of your
process. That means that the following won't work:</p>
<pre><code>$ node -e 'process.env.foo = "bar"' && echo $foo
</code></pre><p>But this will:</p>
<pre><code class="lang-js">process.env.foo = 'bar';
console.log(process.env.foo);
</code></pre>
<p>Assigning a property on <code>process.env</code> will implicitly convert the value
to a string.</p>
<p>Example:</p>
<pre><code class="lang-js">process.env.test = null;
console.log(process.env.test);
// => 'null'
process.env.test = undefined;
console.log(process.env.test);
// => 'undefined'
</code></pre>
<p>Use <code>delete</code> to delete a property from <code>process.env</code>.</p>
<p>Example:</p>
<pre><code class="lang-js">process.env.TEST = 1;
delete process.env.TEST;
console.log(process.env.TEST);
// => undefined
</code></pre>
<h2>process.execArgv<span><a class="mark" href="#process_process_execargv" id="process_process_execargv">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>This is the set of Node.js-specific command line options from the
executable that started the process. These options do not show up in
<code>process.argv</code>, and do not include the Node.js executable, the name of
the script, or any options following the script name. These options
are useful in order to spawn child processes with the same execution
environment as the parent.</p>
<p>Example:</p>
<pre><code>$ node --harmony script.js --version
</code></pre><p>results in process.execArgv:</p>
<pre><code class="lang-js">['--harmony']
</code></pre>
<p>and process.argv:</p>
<pre><code class="lang-js">['/usr/local/bin/node', 'script.js', '--version']
</code></pre>
<h2>process.execPath<span><a class="mark" href="#process_process_execpath" id="process_process_execpath">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.100</span>
</div><p>This is the absolute pathname of the executable that started the process.</p>
<p>Example:</p>
<pre><code>/usr/local/bin/node
</code></pre><h2>process.exit([code])<span><a class="mark" href="#process_process_exit_code" id="process_process_exit_code">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.13</span>
</div><p>Ends the process with the specified <code>code</code>. If omitted, exit uses the
'success' code <code>0</code>.</p>
<p>To exit with a 'failure' code:</p>
<pre><code class="lang-js">process.exit(1);
</code></pre>
<p>The shell that executed Node.js should see the exit code as 1.</p>
<h2>process.exitCode<span><a class="mark" href="#process_process_exitcode" id="process_process_exitcode">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.8</span>
</div><p>A number which will be the process exit code, when the process either
exits gracefully, or is exited via <a href="#process_process_exit_code"><code>process.exit()</code></a> without specifying
a code.</p>
<p>Specifying a code to <code>process.exit(code)</code> will override any previous
setting of <code>process.exitCode</code>.</p>
<h2>process.getegid()<span><a class="mark" href="#process_process_getegid" id="process_process_getegid">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v2.0.0</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Gets the effective group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/getegid.2.html">getegid(2)</a>.)
This is the numerical group id, not the group name.</p>
<pre><code class="lang-js">if (process.getegid) {
console.log(`Current gid: ${process.getegid()}`);
}
</code></pre>
<h2>process.geteuid()<span><a class="mark" href="#process_process_geteuid" id="process_process_geteuid">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v2.0.0</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Gets the effective user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/geteuid.2.html">geteuid(2)</a>.)
This is the numerical userid, not the username.</p>
<pre><code class="lang-js">if (process.geteuid) {
console.log(`Current uid: ${process.geteuid()}`);
}
</code></pre>
<h2>process.getgid()<span><a class="mark" href="#process_process_getgid" id="process_process_getgid">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Gets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/getgid.2.html">getgid(2)</a>.)
This is the numerical group id, not the group name.</p>
<pre><code class="lang-js">if (process.getgid) {
console.log(`Current gid: ${process.getgid()}`);
}
</code></pre>
<h2>process.getgroups()<span><a class="mark" href="#process_process_getgroups" id="process_process_getgroups">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.4</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Returns an array with the supplementary group IDs. POSIX leaves it unspecified
if the effective group ID is included but Node.js ensures it always is.</p>
<h2>process.getuid()<span><a class="mark" href="#process_process_getuid" id="process_process_getuid">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.28</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Gets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/getuid.2.html">getuid(2)</a>.)
This is the numerical userid, not the username.</p>
<pre><code class="lang-js">if (process.getuid) {
console.log(`Current uid: ${process.getuid()}`);
}
</code></pre>
<h2>process.hrtime()<span><a class="mark" href="#process_process_hrtime" id="process_process_hrtime">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.6</span>
</div><p>Returns the current high-resolution real time in a <code>[seconds, nanoseconds]</code>
tuple Array. It is relative to an arbitrary time in the past. It is not
related to the time of day and therefore not subject to clock drift. The
primary use is for measuring performance between intervals.</p>
<p>You may pass in the result of a previous call to <code>process.hrtime()</code> to get
a diff reading, useful for benchmarks and measuring intervals:</p>
<pre><code class="lang-js">var time = process.hrtime();
// [ 1800216, 25 ]
setTimeout(() => {
var diff = process.hrtime(time);
// [ 1, 552 ]
console.log('benchmark took %d nanoseconds', diff[0] * 1e9 + diff[1]);
// benchmark took 1000000527 nanoseconds
}, 1000);
</code></pre>
<h2>process.initgroups(user, extra_group)<span><a class="mark" href="#process_process_initgroups_user_extra_group" id="process_process_initgroups_user_extra_group">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.4</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Reads /etc/group and initializes the group access list, using all groups of
which the user is a member. This is a privileged operation, meaning you need
to be root or have the <code>CAP_SETGID</code> capability.</p>
<p><code>user</code> is a user name or user ID. <code>extra_group</code> is a group name or group ID.</p>
<p>Some care needs to be taken when dropping privileges. Example:</p>
<pre><code class="lang-js">console.log(process.getgroups()); // [ 0 ]
process.initgroups('bnoordhuis', 1000); // switch user
console.log(process.getgroups()); // [ 27, 30, 46, 1000, 0 ]
process.setgid(1000); // drop root gid
console.log(process.getgroups()); // [ 27, 30, 46, 1000 ]
</code></pre>
<h2>process.kill(pid[, signal])<span><a class="mark" href="#process_process_kill_pid_signal" id="process_process_kill_pid_signal">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.6</span>
</div><p>Send a signal to a process. <code>pid</code> is the process id and <code>signal</code> is the
string describing the signal to send. Signal names are strings like
<code>SIGINT</code> or <code>SIGHUP</code>. If omitted, the signal will be <code>SIGTERM</code>.
See <a href="#process_signal_events">Signal Events</a> and <a href="http://man7.org/linux/man-pages/man2/kill.2.html">kill(2)</a> for more information.</p>
<p>Will throw an error if target does not exist, and as a special case, a signal
of <code>0</code> can be used to test for the existence of a process. Windows platforms
will throw an error if the <code>pid</code> is used to kill a process group.</p>
<p>Note that even though the name of this function is <code>process.kill</code>, it is really
just a signal sender, like the <code>kill</code> system call. The signal sent may do
something other than kill the target process.</p>
<p>Example of sending a signal to yourself:</p>
<pre><code class="lang-js">process.on('SIGHUP', () => {
console.log('Got SIGHUP signal.');
});
setTimeout(() => {
console.log('Exiting.');
process.exit(0);
}, 100);
process.kill(process.pid, 'SIGHUP');
</code></pre>
<p>Note: When SIGUSR1 is received by Node.js it starts the debugger, see
<a href="#process_signal_events">Signal Events</a>.</p>
<h2>process.mainModule<span><a class="mark" href="#process_process_mainmodule" id="process_process_mainmodule">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.17</span>
</div><p>Alternate way to retrieve <a href="modules.html#modules_accessing_the_main_module"><code>require.main</code></a>. The difference is that if the main
module changes at runtime, <code>require.main</code> might still refer to the original main
module in modules that were required before the change occurred. Generally it's
safe to assume that the two refer to the same module.</p>
<p>As with <code>require.main</code>, it will be <code>undefined</code> if there was no entry script.</p>
<h2>process.memoryUsage()<span><a class="mark" href="#process_process_memoryusage" id="process_process_memoryusage">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>rss</code> <span class="type"><Integer></span></li>
<li><code>heapTotal</code> <span class="type"><Integer></span></li>
<li><code>heapUsed</code> <span class="type"><Integer></span></li>
<li><code>external</code> <span class="type"><Integer></span></li>
</ul>
</li>
</ul>
<p>The <code>process.memoryUsage()</code> method returns an object describing the memory usage
of the Node.js process measured in bytes.</p>
<p>For example, the code:</p>
<pre><code class="lang-js">console.log(process.memoryUsage());
</code></pre>
<p>This will generate:</p>
<pre><code class="lang-js">{ rss: 4935680,
heapTotal: 1826816,
heapUsed: 650472,
external: 49879
}
</code></pre>
<p><code>heapTotal</code> and <code>heapUsed</code> refer to V8's memory usage.
<code>external</code> refers to the memory usage of C++ objects bound to JavaScript
objects managed by V8.</p>
<h2>process.nextTick(callback[, arg][, ...])<span><a class="mark" href="#process_process_nexttick_callback_arg" id="process_process_nexttick_callback_arg">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.26</span>
</div><ul>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Once the current event loop turn runs to completion, call the callback
function.</p>
<p>This is <em>not</em> a simple alias to <a href="timers.html#timers_settimeout_callback_delay_arg"><code>setTimeout(fn, 0)</code></a>, it's much more
efficient. It runs before any additional I/O events (including
timers) fire in subsequent ticks of the event loop.</p>
<pre><code class="lang-js">console.log('start');
process.nextTick(() => {
console.log('nextTick callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// nextTick callback
</code></pre>
<p>This is important in developing APIs where you want to give the user the
chance to assign event handlers after an object has been constructed,
but before any I/O has occurred.</p>
<pre><code class="lang-js">function MyThing(options) {
this.setupOptions(options);
process.nextTick(() => {
this.startDoingStuff();
});
}
var thing = new MyThing();
thing.getReadyForStuff();
// thing.startDoingStuff() gets called now, not before.
</code></pre>
<p>It is very important for APIs to be either 100% synchronous or 100%
asynchronous. Consider this example:</p>
<pre><code class="lang-js">// WARNING! DO NOT USE! BAD UNSAFE HAZARD!
function maybeSync(arg, cb) {
if (arg) {
cb();
return;
}
fs.stat('file', cb);
}
</code></pre>
<p>This API is hazardous. If you do this:</p>
<pre><code class="lang-js">maybeSync(true, () => {
foo();
});
bar();
</code></pre>
<p>then it's not clear whether <code>foo()</code> or <code>bar()</code> will be called first.</p>
<p>This approach is much better:</p>
<pre><code class="lang-js">function definitelyAsync(arg, cb) {
if (arg) {
process.nextTick(cb);
return;
}
fs.stat('file', cb);
}
</code></pre>
<p>Note: the nextTick queue is completely drained on each pass of the
event loop <strong>before</strong> additional I/O is processed. As a result,
recursively setting nextTick callbacks will block any I/O from
happening, just like a <code>while(true);</code> loop.</p>
<h2>process.pid<span><a class="mark" href="#process_process_pid" id="process_process_pid">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.15</span>
</div><p>The PID of the process.</p>
<pre><code class="lang-js">console.log(`This process is pid ${process.pid}`);
</code></pre>
<h2>process.platform<span><a class="mark" href="#process_process_platform" id="process_process_platform">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.16</span>
</div><p>What platform you're running on:
<code>'darwin'</code>, <code>'freebsd'</code>, <code>'linux'</code>, <code>'sunos'</code> or <code>'win32'</code></p>
<pre><code class="lang-js">console.log(`This platform is ${process.platform}`);
</code></pre>
<h2>process.release<span><a class="mark" href="#process_process_release" id="process_process_release">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v3.0.0</span>
</div><p>An Object containing metadata related to the current release, including URLs
for the source tarball and headers-only tarball.</p>
<p><code>process.release</code> contains the following properties:</p>
<ul>
<li><code>name</code>: a string with a value that will always be <code>'node'</code> for Node.js. For
legacy io.js releases, this will be <code>'io.js'</code>.</li>
<li><code>sourceUrl</code>: a complete URL pointing to a <em>.tar.gz</em> file containing the
source of the current release.</li>
<li><code>headersUrl</code>: a complete URL pointing to a <em>.tar.gz</em> file containing only
the header files for the current release. This file is significantly smaller
than the full source file and can be used for compiling add-ons against
Node.js.</li>
<li><code>libUrl</code>: a complete URL pointing to an <em>node.lib</em> file matching the
architecture and version of the current release. This file is used for
compiling add-ons against Node.js. <em>This property is only present on Windows
builds of Node.js and will be missing on all other platforms.</em></li>
</ul>
<p>e.g.</p>
<pre><code class="lang-js">{ name: 'node',
sourceUrl: 'https://nodejs.org/download/release/v4.0.0/node-v4.0.0.tar.gz',
headersUrl: 'https://nodejs.org/download/release/v4.0.0/node-v4.0.0-headers.tar.gz',
libUrl: 'https://nodejs.org/download/release/v4.0.0/win-x64/node.lib' }
</code></pre>
<p>In custom builds from non-release versions of the source tree, only the
<code>name</code> property may be present. The additional properties should not be
relied upon to exist.</p>
<h2>process.send(message[, sendHandle][, callback])<span><a class="mark" href="#process_process_send_message_sendhandle_callback" id="process_process_send_message_sendhandle_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div><ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>sendHandle</code> <span class="type"><Handle object></span></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>When Node.js is spawned with an IPC channel attached, it can send messages to its
parent process using <code>process.send()</code>. Each will be received as a
<a href="child_process.html#child_process_event_message"><code>'message'</code></a> event on the parent's <code>ChildProcess</code> object.</p>
<p><em>Note: this function uses <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify"><code>JSON.stringify()</code></a> internally to serialize the <code>message</code>.</em></p>
<p>If Node.js was not spawned with an IPC channel, <code>process.send()</code> will be undefined.</p>
<h2>process.setegid(id)<span><a class="mark" href="#process_process_setegid_id" id="process_process_setegid_id">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v2.0.0</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Sets the effective group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setegid.2.html">setegid(2)</a>.)
This accepts either a numerical ID or a groupname string. If a groupname
is specified, this method blocks while resolving it to a numerical ID.</p>
<pre><code class="lang-js">if (process.getegid && process.setegid) {
console.log(`Current gid: ${process.getegid()}`);
try {
process.setegid(501);
console.log(`New gid: ${process.getegid()}`);
}
catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}
</code></pre>
<h2>process.seteuid(id)<span><a class="mark" href="#process_process_seteuid_id" id="process_process_seteuid_id">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v2.0.0</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Sets the effective user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/seteuid.2.html">seteuid(2)</a>.)
This accepts either a numerical ID or a username string. If a username
is specified, this method blocks while resolving it to a numerical ID.</p>
<pre><code class="lang-js">if (process.geteuid && process.seteuid) {
console.log(`Current uid: ${process.geteuid()}`);
try {
process.seteuid(501);
console.log(`New uid: ${process.geteuid()}`);
}
catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}
</code></pre>
<h2>process.setgid(id)<span><a class="mark" href="#process_process_setgid_id" id="process_process_setgid_id">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.31</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html">setgid(2)</a>.) This accepts either
a numerical ID or a groupname string. If a groupname is specified, this method
blocks while resolving it to a numerical ID.</p>
<pre><code class="lang-js">if (process.getgid && process.setgid) {
console.log(`Current gid: ${process.getgid()}`);
try {
process.setgid(501);
console.log(`New gid: ${process.getgid()}`);
}
catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}
</code></pre>
<h2>process.setgroups(groups)<span><a class="mark" href="#process_process_setgroups_groups" id="process_process_setgroups_groups">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.4</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Sets the supplementary group IDs. This is a privileged operation, meaning you
need to be root or have the <code>CAP_SETGID</code> capability.</p>
<p>The list can contain group IDs, group names or both.</p>
<h2>process.setuid(id)<span><a class="mark" href="#process_process_setuid_id" id="process_process_setuid_id">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.28</span>
</div><p>Note: this function is only available on POSIX platforms (i.e. not Windows,
Android)</p>
<p>Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html">setuid(2)</a>.) This accepts either
a numerical ID or a username string. If a username is specified, this method
blocks while resolving it to a numerical ID.</p>
<pre><code class="lang-js">if (process.getuid && process.setuid) {
console.log(`Current uid: ${process.getuid()}`);
try {
process.setuid(501);
console.log(`New uid: ${process.getuid()}`);
}
catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}
</code></pre>
<h2>process.stderr<span><a class="mark" href="#process_process_stderr" id="process_process_stderr">#</a></span></h2>
<p>A writable stream to stderr (on fd <code>2</code>).</p>
<p><code>process.stderr</code> and <code>process.stdout</code> are unlike other streams in Node.js in
that they cannot be closed (<code>end()</code> will throw), they never emit the <code>finish</code>
event and that writes can block when output is redirected to a file (although
disks are fast and operating systems normally employ write-back caching so it
should be a very rare occurrence indeed.)</p>
<p>Additionally, <code>process.stderr</code> and <code>process.stdout</code> are blocking when outputting
to TTYs (terminals) on OS X as a workaround for the OS's very small, 1kb
buffer size. This is to prevent interleaving between <code>stdout</code> and <code>stderr</code>.</p>
<h2>process.stdin<span><a class="mark" href="#process_process_stdin" id="process_process_stdin">#</a></span></h2>
<p>A <code>Readable Stream</code> for stdin (on fd <code>0</code>).</p>
<p>Example of opening standard input and listening for both events:</p>
<pre><code class="lang-js">process.stdin.setEncoding('utf8');
process.stdin.on('readable', () => {
var chunk = process.stdin.read();
if (chunk !== null) {
process.stdout.write(`data: ${chunk}`);
}
});
process.stdin.on('end', () => {
process.stdout.write('end');
});
</code></pre>
<p>As a Stream, <code>process.stdin</code> can also be used in "old" mode that is compatible
with scripts written for node.js prior to v0.10.
For more information see <a href="stream.html#stream_compatibility_with_older_node_js_versions">Stream compatibility</a>.</p>
<p>In "old" Streams mode the stdin stream is paused by default, so one
must call <code>process.stdin.resume()</code> to read from it. Note also that calling
<code>process.stdin.resume()</code> itself would switch stream to "old" mode.</p>
<p>If you are starting a new project you should prefer a more recent "new" Streams
mode over "old" one.</p>
<h2>process.stdout<span><a class="mark" href="#process_process_stdout" id="process_process_stdout">#</a></span></h2>
<p>A <code>Writable Stream</code> to <code>stdout</code> (on fd <code>1</code>).</p>
<p>For example, a <code>console.log</code> equivalent could look like this:</p>
<pre><code class="lang-js">console.log = (msg) => {
process.stdout.write(`${msg}\n`);
};
</code></pre>
<p><code>process.stderr</code> and <code>process.stdout</code> are unlike other streams in Node.js in
that they cannot be closed (<code>end()</code> will throw), they never emit the <code>'finish'</code>
event and that writes can block when output is redirected to a file (although
disks are fast and operating systems normally employ write-back caching so it
should be a very rare occurrence indeed.)</p>
<p>Additionally, <code>process.stderr</code> and <code>process.stdout</code> are blocking when outputting
to TTYs (terminals) on OS X as a workaround for the OS's very small, 1kb
buffer size. This is to prevent interleaving between <code>stdout</code> and <code>stderr</code>.</p>
<p>To check if Node.js is being run in a TTY context, read the <code>isTTY</code> property
on <code>process.stderr</code>, <code>process.stdout</code>, or <code>process.stdin</code>:</p>
<pre><code>$ node -p "Boolean(process.stdin.isTTY)"
true
$ echo "foo" | node -p "Boolean(process.stdin.isTTY)"
false
$ node -p "Boolean(process.stdout.isTTY)"
true
$ node -p "Boolean(process.stdout.isTTY)" | cat
false
</code></pre><p>See <a href="tty.html#tty_tty">the tty docs</a> for more information.</p>
<h2>process.title<span><a class="mark" href="#process_process_title" id="process_process_title">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.104</span>
</div><p>Getter/setter to set what is displayed in <code>ps</code>.</p>
<p>When used as a setter, the maximum length is platform-specific and probably
short.</p>
<p>On Linux and OS X, it's limited to the size of the binary name plus the
length of the command line arguments because it overwrites the argv memory.</p>
<p>v0.8 allowed for longer process title strings by also overwriting the environ
memory but that was potentially insecure/confusing in some (rather obscure)
cases.</p>
<h2>process.umask([mask])<span><a class="mark" href="#process_process_umask_mask" id="process_process_umask_mask">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.19</span>
</div><p>Sets or reads the process's file mode creation mask. Child processes inherit
the mask from the parent process. Returns the old mask if <code>mask</code> argument is
given, otherwise returns the current mask.</p>
<pre><code class="lang-js">const newmask = 0o022;
const oldmask = process.umask(newmask);
console.log(
`Changed umask from ${oldmask.toString(8)} to ${newmask.toString(8)}`
);
</code></pre>
<h2>process.uptime()<span><a class="mark" href="#process_process_uptime" id="process_process_uptime">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.0</span>
</div><p>Number of seconds Node.js has been running.</p>
<h2>process.version<span><a class="mark" href="#process_process_version" id="process_process_version">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.3</span>
</div><p>A compiled-in property that exposes <code>NODE_VERSION</code>.</p>
<pre><code class="lang-js">console.log(`Version: ${process.version}`);
</code></pre>
<h2>process.versions<span><a class="mark" href="#process_process_versions" id="process_process_versions">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.2.0</span>
</div><p>A property exposing version strings of Node.js and its dependencies.</p>
<pre><code class="lang-js">console.log(process.versions);
</code></pre>
<p>Will print something like:</p>
<pre><code class="lang-js">{ http_parser: '2.3.0',
node: '1.1.1',
v8: '4.1.0.14',
uv: '1.3.0',
zlib: '1.2.8',
ares: '1.10.0-DEV',
modules: '43',
icu: '55.1',
openssl: '1.0.1k' }
</code></pre>
<!-- [end-include:process.md] -->
<!-- [start-include:punycode.md] -->
<h1>Punycode<span><a class="mark" href="#punycode_punycode" id="punycode_punycode">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p><a href="https://mths.be/punycode">Punycode.js</a> is bundled with Node.js v0.5.1+. Use <code>require('punycode')</code> to
access it. (To use it with other Node.js versions, use npm to install the
<code>punycode</code> module first.)</p>
<h2>punycode.decode(string)<span><a class="mark" href="#punycode_punycode_decode_string" id="punycode_punycode_decode_string">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.1</span>
</div><p>Converts a Punycode string of ASCII-only symbols to a string of Unicode symbols.</p>
<pre><code class="lang-js">// decode domain name parts
punycode.decode('maana-pta'); // 'mañana'
punycode.decode('--dqo34k'); // '☃-⌘'
</code></pre>
<h2>punycode.encode(string)<span><a class="mark" href="#punycode_punycode_encode_string" id="punycode_punycode_encode_string">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.1</span>
</div><p>Converts a string of Unicode symbols to a Punycode string of ASCII-only symbols.</p>
<pre><code class="lang-js">// encode domain name parts
punycode.encode('mañana'); // 'maana-pta'
punycode.encode('☃-⌘'); // '--dqo34k'
</code></pre>
<h2>punycode.toASCII(domain)<span><a class="mark" href="#punycode_punycode_toascii_domain" id="punycode_punycode_toascii_domain">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.1</span>
</div><p>Converts a Unicode string representing a domain name to Punycode. Only the
non-ASCII parts of the domain name will be converted, i.e. it doesn't matter if
you call it with a domain that's already in ASCII.</p>
<pre><code class="lang-js">// encode domain names
punycode.toASCII('mañana.com'); // 'xn--maana-pta.com'
punycode.toASCII('☃-⌘.com'); // 'xn----dqo34k.com'
</code></pre>
<h2>punycode.toUnicode(domain)<span><a class="mark" href="#punycode_punycode_tounicode_domain" id="punycode_punycode_tounicode_domain">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.1</span>
</div><p>Converts a Punycode string representing a domain name to Unicode. Only the
Punycoded parts of the domain name will be converted, i.e. it doesn't matter if
you call it on a string that has already been converted to Unicode.</p>
<pre><code class="lang-js">// decode domain names
punycode.toUnicode('xn--maana-pta.com'); // 'mañana.com'
punycode.toUnicode('xn----dqo34k.com'); // '☃-⌘.com'
</code></pre>
<h2>punycode.ucs2<span><a class="mark" href="#punycode_punycode_ucs2" id="punycode_punycode_ucs2">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><h3>punycode.ucs2.decode(string)<span><a class="mark" href="#punycode_punycode_ucs2_decode_string" id="punycode_punycode_ucs2_decode_string">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p>Creates an array containing the numeric code point values of each Unicode
symbol in the string. While <a href="https://mathiasbynens.be/notes/javascript-encoding">JavaScript uses UCS-2 internally</a>, this function
will convert a pair of surrogate halves (each of which UCS-2 exposes as
separate characters) into a single code point, matching UTF-16.</p>
<pre><code class="lang-js">punycode.ucs2.decode('abc'); // [0x61, 0x62, 0x63]
// surrogate pair for U+1D306 tetragram for centre:
punycode.ucs2.decode('\uD834\uDF06'); // [0x1D306]
</code></pre>
<h3>punycode.ucs2.encode(codePoints)<span><a class="mark" href="#punycode_punycode_ucs2_encode_codepoints" id="punycode_punycode_ucs2_encode_codepoints">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p>Creates a string based on an array of numeric code point values.</p>
<pre><code class="lang-js">punycode.ucs2.encode([0x61, 0x62, 0x63]); // 'abc'
punycode.ucs2.encode([0x1D306]); // '\uD834\uDF06'
</code></pre>
<h2>punycode.version<span><a class="mark" href="#punycode_punycode_version" id="punycode_punycode_version">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.1</span>
</div><p>A string representing the current Punycode.js version number.</p>
<!-- [end-include:punycode.md] -->
<!-- [start-include:querystring.md] -->
<h1>Query String<span><a class="mark" href="#querystring_query_string" id="querystring_query_string">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><!--name=querystring-->
<p>This module provides utilities for dealing with query strings.
It provides the following methods:</p>
<h2>querystring.escape<span><a class="mark" href="#querystring_querystring_escape" id="querystring_querystring_escape">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>The escape function used by <code>querystring.stringify</code>,
provided so that it could be overridden if necessary.</p>
<h2>querystring.parse(str[, sep][, eq][, options])<span><a class="mark" href="#querystring_querystring_parse_str_sep_eq_options" id="querystring_querystring_parse_str_sep_eq_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>Deserialize a query string to an object.
Optionally override the default separator (<code>'&'</code>) and assignment (<code>'='</code>)
characters.</p>
<p>Options object may contain <code>maxKeys</code> property (equal to 1000 by default), it'll
be used to limit processed keys. Set it to 0 to remove key count limitation.</p>
<p>Options object may contain <code>decodeURIComponent</code> property (<code>querystring.unescape</code> by default),
it can be used to decode a <code>non-utf8</code> encoding string if necessary.</p>
<p>Example:</p>
<pre><code class="lang-js">querystring.parse('foo=bar&baz=qux&baz=quux&corge')
// returns { foo: 'bar', baz: ['qux', 'quux'], corge: '' }
// Suppose gbkDecodeURIComponent function already exists,
// it can decode `gbk` encoding string
querystring.parse('w=%D6%D0%CE%C4&foo=bar', null, null,
{ decodeURIComponent: gbkDecodeURIComponent })
// returns { w: 'ä¸æ–‡', foo: 'bar' }
</code></pre>
<h2>querystring.stringify(obj[, sep][, eq][, options])<span><a class="mark" href="#querystring_querystring_stringify_obj_sep_eq_options" id="querystring_querystring_stringify_obj_sep_eq_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>Serialize an object to a query string.
Optionally override the default separator (<code>'&'</code>) and assignment (<code>'='</code>)
characters.</p>
<p>Options object may contain <code>encodeURIComponent</code> property (<code>querystring.escape</code> by default),
it can be used to encode string with <code>non-utf8</code> encoding if necessary.</p>
<p>Example:</p>
<pre><code class="lang-js">querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], corge: '' })
// returns 'foo=bar&baz=qux&baz=quux&corge='
querystring.stringify({foo: 'bar', baz: 'qux'}, ';', ':')
// returns 'foo:bar;baz:qux'
// Suppose gbkEncodeURIComponent function already exists,
// it can encode string with `gbk` encoding
querystring.stringify({ w: 'ä¸æ–‡', foo: 'bar' }, null, null,
{ encodeURIComponent: gbkEncodeURIComponent })
// returns 'w=%D6%D0%CE%C4&foo=bar'
</code></pre>
<h2>querystring.unescape<span><a class="mark" href="#querystring_querystring_unescape" id="querystring_querystring_unescape">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>The unescape function used by <code>querystring.parse</code>,
provided so that it could be overridden if necessary.</p>
<p>It will try to use <code>decodeURIComponent</code> in the first place,
but if that fails it falls back to a safer equivalent that
doesn't throw on malformed URLs.</p>
<!-- [end-include:querystring.md] -->
<!-- [start-include:readline.md] -->
<h1>Readline<span><a class="mark" href="#readline_readline" id="readline_readline">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>To use this module, do <code>require('readline')</code>. Readline allows reading of a
stream (such as <a href="process.html#process_process_stdin"><code>process.stdin</code></a>) on a line-by-line basis.</p>
<p>Note that once you've invoked this module, your Node.js program will not
terminate until you've closed the interface. Here's how to allow your
program to gracefully exit:</p>
<pre><code class="lang-js">const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
rl.question('What do you think of Node.js? ', (answer) => {
// TODO: Log the answer in a database
console.log('Thank you for your valuable feedback:', answer);
rl.close();
});
</code></pre>
<h2>Class: Interface<span><a class="mark" href="#readline_class_interface" id="readline_class_interface">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.104</span>
</div><p>The class that represents a readline interface with an input and output
stream.</p>
<h3>rl.close()<span><a class="mark" href="#readline_rl_close" id="readline_rl_close">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.98</span>
</div><p>Closes the <code>Interface</code> instance, relinquishing control on the <code>input</code> and
<code>output</code> streams. The <code>'close'</code> event will also be emitted.</p>
<h3>rl.pause()<span><a class="mark" href="#readline_rl_pause" id="readline_rl_pause">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><p>Pauses the readline <code>input</code> stream, allowing it to be resumed later if needed.</p>
<p>Note that this doesn't immediately pause the stream of events. Several events may
be emitted after calling <code>pause</code>, including <code>line</code>.</p>
<h3>rl.prompt([preserveCursor])<span><a class="mark" href="#readline_rl_prompt_preservecursor" id="readline_rl_prompt_preservecursor">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.98</span>
</div><p>Readies readline for input from the user, putting the current <code>setPrompt</code>
options on a new line, giving the user a new spot to write. Set <code>preserveCursor</code>
to <code>true</code> to prevent the cursor placement being reset to <code>0</code>.</p>
<p>This will also resume the <code>input</code> stream used with <code>createInterface</code> if it has
been paused.</p>
<p>If <code>output</code> is set to <code>null</code> or <code>undefined</code> when calling <code>createInterface</code>, the
prompt is not written.</p>
<h3>rl.question(query, callback)<span><a class="mark" href="#readline_rl_question_query_callback" id="readline_rl_question_query_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.3</span>
</div><p>Prepends the prompt with <code>query</code> and invokes <code>callback</code> with the user's
response. Displays the query to the user, and then invokes <code>callback</code>
with the user's response after it has been typed.</p>
<p>This will also resume the <code>input</code> stream used with <code>createInterface</code> if
it has been paused.</p>
<p>If <code>output</code> is set to <code>null</code> or <code>undefined</code> when calling <code>createInterface</code>,
nothing is displayed.</p>
<p>Example usage:</p>
<pre><code class="lang-js">rl.question('What is your favorite food?', (answer) => {
console.log(`Oh, so your favorite food is ${answer}`);
});
</code></pre>
<h3>rl.resume()<span><a class="mark" href="#readline_rl_resume" id="readline_rl_resume">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.4</span>
</div><p>Resumes the readline <code>input</code> stream.</p>
<h3>rl.setPrompt(prompt)<span><a class="mark" href="#readline_rl_setprompt_prompt" id="readline_rl_setprompt_prompt">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.98</span>
</div><p>Sets the prompt, for example when you run <code>node</code> on the command line, you see
<code>></code>, which is Node.js's prompt.</p>
<h3>rl.write(data[, key])<span><a class="mark" href="#readline_rl_write_data_key" id="readline_rl_write_data_key">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.98</span>
</div><p>Writes <code>data</code> to <code>output</code> stream, unless <code>output</code> is set to <code>null</code> or
<code>undefined</code> when calling <code>createInterface</code>. <code>key</code> is an object literal to
represent a key sequence; available if the terminal is a TTY.</p>
<p>This will also resume the <code>input</code> stream if it has been paused.</p>
<p>Example:</p>
<pre><code class="lang-js">rl.write('Delete me!');
// Simulate ctrl+u to delete the line written previously
rl.write(null, {ctrl: true, name: 'u'});
</code></pre>
<h2>Events<span><a class="mark" href="#readline_events" id="readline_events">#</a></span></h2>
<h3>Event: 'close'<span><a class="mark" href="#readline_event_close" id="readline_event_close">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.98</span>
</div><p><code>function () {}</code></p>
<p>Emitted when <code>close()</code> is called.</p>
<p>Also emitted when the <code>input</code> stream receives its <code>'end'</code> event. The <code>Interface</code>
instance should be considered "finished" once this is emitted. For example, when
the <code>input</code> stream receives <code>^D</code>, respectively known as <code>EOT</code>.</p>
<p>This event is also called if there is no <code>SIGINT</code> event listener present when
the <code>input</code> stream receives a <code>^C</code>, respectively known as <code>SIGINT</code>.</p>
<h3>Event: 'line'<span><a class="mark" href="#readline_event_line" id="readline_event_line">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.98</span>
</div><p><code>function (line) {}</code></p>
<p>Emitted whenever the <code>input</code> stream receives an end of line (<code>\n</code>, <code>\r</code>, or
<code>\r\n</code>), usually received when the user hits enter, or return. This is a good
hook to listen for user input.</p>
<p>Example of listening for <code>'line'</code>:</p>
<pre><code class="lang-js">rl.on('line', (cmd) => {
console.log(`You just typed: ${cmd}`);
});
</code></pre>
<h3>Event: 'pause'<span><a class="mark" href="#readline_event_pause" id="readline_event_pause">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.5</span>
</div><p><code>function () {}</code></p>
<p>Emitted whenever the <code>input</code> stream is paused.</p>
<p>Also emitted whenever the <code>input</code> stream is not paused and receives the
<code>SIGCONT</code> event. (See events <code>SIGTSTP</code> and <code>SIGCONT</code>)</p>
<p>Example of listening for <code>'pause'</code>:</p>
<pre><code class="lang-js">rl.on('pause', () => {
console.log('Readline paused.');
});
</code></pre>
<h3>Event: 'resume'<span><a class="mark" href="#readline_event_resume" id="readline_event_resume">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.5</span>
</div><p><code>function () {}</code></p>
<p>Emitted whenever the <code>input</code> stream is resumed.</p>
<p>Example of listening for <code>'resume'</code>:</p>
<pre><code class="lang-js">rl.on('resume', () => {
console.log('Readline resumed.');
});
</code></pre>
<h3>Event: 'SIGCONT'<span><a class="mark" href="#readline_event_sigcont" id="readline_event_sigcont">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.5</span>
</div><p><code>function () {}</code></p>
<p><strong>This does not work on Windows.</strong></p>
<p>Emitted whenever the <code>input</code> stream is sent to the background with <code>^Z</code>,
respectively known as <code>SIGTSTP</code>, and then continued with <a href="http://man7.org/linux/man-pages/man1/fg.1.html">fg(1)</a>. This event
only emits if the stream was not paused before sending the program to the
background.</p>
<p>Example of listening for <code>SIGCONT</code>:</p>
<pre><code class="lang-js">rl.on('SIGCONT', () => {
// `prompt` will automatically resume the stream
rl.prompt();
});
</code></pre>
<h3>Event: 'SIGINT'<span><a class="mark" href="#readline_event_sigint" id="readline_event_sigint">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p><code>function () {}</code></p>
<p>Emitted whenever the <code>input</code> stream receives a <code>^C</code>, respectively known as
<code>SIGINT</code>. If there is no <code>SIGINT</code> event listener present when the <code>input</code>
stream receives a <code>SIGINT</code>, <code>pause</code> will be triggered.</p>
<p>Example of listening for <code>SIGINT</code>:</p>
<pre><code class="lang-js">rl.on('SIGINT', () => {
rl.question('Are you sure you want to exit?', (answer) => {
if (answer.match(/^y(es)?$/i)) rl.pause();
});
});
</code></pre>
<h3>Event: 'SIGTSTP'<span><a class="mark" href="#readline_event_sigtstp" id="readline_event_sigtstp">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.5</span>
</div><p><code>function () {}</code></p>
<p><strong>This does not work on Windows.</strong></p>
<p>Emitted whenever the <code>input</code> stream receives a <code>^Z</code>, respectively known as
<code>SIGTSTP</code>. If there is no <code>SIGTSTP</code> event listener present when the <code>input</code>
stream receives a <code>SIGTSTP</code>, the program will be sent to the background.</p>
<p>When the program is resumed with <code>fg</code>, the <code>'pause'</code> and <code>SIGCONT</code> events will be
emitted. You can use either to resume the stream.</p>
<p>The <code>'pause'</code> and <code>SIGCONT</code> events will not be triggered if the stream was paused
before the program was sent to the background.</p>
<p>Example of listening for <code>SIGTSTP</code>:</p>
<pre><code class="lang-js">rl.on('SIGTSTP', () => {
// This will override SIGTSTP and prevent the program from going to the
// background.
console.log('Caught SIGTSTP.');
});
</code></pre>
<h2>Example: Tiny CLI<span><a class="mark" href="#readline_example_tiny_cli" id="readline_example_tiny_cli">#</a></span></h2>
<p>Here's an example of how to use all these together to craft a tiny command
line interface:</p>
<pre><code class="lang-js">const readline = require('readline');
const rl = readline.createInterface(process.stdin, process.stdout);
rl.setPrompt('OHAI> ');
rl.prompt();
rl.on('line', (line) => {
switch(line.trim()) {
case 'hello':
console.log('world!');
break;
default:
console.log('Say what? I might have heard `' + line.trim() + '`');
break;
}
rl.prompt();
}).on('close', () => {
console.log('Have a great day!');
process.exit(0);
});
</code></pre>
<h2>Example: Read File Stream Line-by-Line<span><a class="mark" href="#readline_example_read_file_stream_line_by_line" id="readline_example_read_file_stream_line_by_line">#</a></span></h2>
<p>A common case for <code>readline</code>'s <code>input</code> option is to pass a filesystem readable
stream to it. This is how one could craft line-by-line parsing of a file:</p>
<pre><code class="lang-js">const readline = require('readline');
const fs = require('fs');
const rl = readline.createInterface({
input: fs.createReadStream('sample.txt')
});
rl.on('line', (line) => {
console.log('Line from file:', line);
});
</code></pre>
<p><em>Note</em>: The <code>rl.write()</code> method will write the data to the <code>readline</code>
Interface's <code>input</code> <em>as if it were provided by the user</em>.</p>
<h2>readline.clearLine(stream, dir)<span><a class="mark" href="#readline_readline_clearline_stream_dir" id="readline_readline_clearline_stream_dir">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>Clears current line of given TTY stream in a specified direction.
<code>dir</code> should have one of following values:</p>
<ul>
<li><code>-1</code> - to the left from cursor</li>
<li><code>1</code> - to the right from cursor</li>
<li><code>0</code> - the entire line</li>
</ul>
<h2>readline.clearScreenDown(stream)<span><a class="mark" href="#readline_readline_clearscreendown_stream" id="readline_readline_clearscreendown_stream">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>Clears the screen from the current position of the cursor down.</p>
<h2>readline.createInterface(options)<span><a class="mark" href="#readline_readline_createinterface_options" id="readline_readline_createinterface_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.98</span>
</div><p>Creates a readline <code>Interface</code> instance. Accepts an <code>options</code> Object that takes
the following values:</p>
<ul>
<li><p><code>input</code> - the readable stream to listen to (Required).</p>
</li>
<li><p><code>output</code> - the writable stream to write readline data to (Optional).</p>
</li>
<li><p><code>completer</code> - an optional function that is used for Tab autocompletion. See
below for an example of using this.</p>
</li>
<li><p><code>terminal</code> - pass <code>true</code> if the <code>input</code> and <code>output</code> streams should be
treated like a TTY, and have ANSI/VT100 escape codes written to it.
Defaults to checking <code>isTTY</code> on the <code>output</code> stream upon instantiation.</p>
</li>
<li><p><code>historySize</code> - maximum number of history lines retained. Defaults to <code>30</code>.</p>
</li>
</ul>
<p>The <code>completer</code> function is given the current line entered by the user, and
is supposed to return an Array with 2 entries:</p>
<ol>
<li><p>An Array with matching entries for the completion.</p>
</li>
<li><p>The substring that was used for the matching.</p>
</li>
</ol>
<p>Which ends up looking something like:
<code>[[substr1, substr2, ...], originalsubstring]</code>.</p>
<p>Example:</p>
<pre><code class="lang-js">function completer(line) {
var completions = '.help .error .exit .quit .q'.split(' ')
var hits = completions.filter((c) => { return c.indexOf(line) == 0 })
// show all completions if none found
return [hits.length ? hits : completions, line]
}
</code></pre>
<p>Also <code>completer</code> can be run in async mode if it accepts two arguments:</p>
<pre><code class="lang-js">function completer(linePartial, callback) {
callback(null, [['123'], linePartial]);
}
</code></pre>
<p><code>createInterface</code> is commonly used with <a href="process.html#process_process_stdin"><code>process.stdin</code></a> and
<a href="process.html#process_process_stdout"><code>process.stdout</code></a> in order to accept user input:</p>
<pre><code class="lang-js">const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
</code></pre>
<p>Once you have a readline instance, you most commonly listen for the
<code>'line'</code> event.</p>
<p>If <code>terminal</code> is <code>true</code> for this instance then the <code>output</code> stream will get
the best compatibility if it defines an <code>output.columns</code> property, and fires
a <code>'resize'</code> event on the <code>output</code> if/when the columns ever change
(<a href="process.html#process_process_stdout"><code>process.stdout</code></a> does this automatically when it is a TTY).</p>
<h2>readline.cursorTo(stream, x, y)<span><a class="mark" href="#readline_readline_cursorto_stream_x_y" id="readline_readline_cursorto_stream_x_y">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>Move cursor to the specified position in a given TTY stream.</p>
<h2>readline.emitKeypressEvents(stream[, interface])<span><a class="mark" href="#readline_readline_emitkeypressevents_stream_interface" id="readline_readline_emitkeypressevents_stream_interface">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>Causes <code>stream</code> to begin emitting <code>'keypress'</code> events corresponding to its
input.
Optionally, <code>interface</code> specifies a <code>readline.Interface</code> instance for which
autocompletion is disabled when copy-pasted input is detected.</p>
<h2>readline.moveCursor(stream, dx, dy)<span><a class="mark" href="#readline_readline_movecursor_stream_dx_dy" id="readline_readline_movecursor_stream_dx_dy">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>Move cursor relative to it's current position in a given TTY stream.</p>
<!-- [end-include:readline.md] -->
<!-- [start-include:repl.md] -->
<h1>REPL<span><a class="mark" href="#repl_repl" id="repl_repl">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>A Read-Eval-Print-Loop (REPL) is available both as a standalone program and
easily includable in other programs. The REPL provides a way to interactively
run JavaScript and see the results. It can be used for debugging, testing, or
just trying things out.</p>
<p>By executing <code>node</code> without any arguments from the command-line you will be
dropped into the REPL. It has simplistic emacs line-editing.</p>
<pre><code>$ node
Type '.help' for options.
> a = [1, 2, 3];
[ 1, 2, 3 ]
> a.forEach((v) => {
... console.log(v);
... });
1
2
3
</code></pre><p>For advanced line-editors, start Node.js with the environmental variable
<code>NODE_NO_READLINE=1</code>. This will start the main and debugger REPL in canonical
terminal settings which will allow you to use with <code>rlwrap</code>.</p>
<p>For example, you could add this to your bashrc file:</p>
<pre><code>alias node="env NODE_NO_READLINE=1 rlwrap node"
</code></pre><h2>Environment Variable Options<span><a class="mark" href="#repl_environment_variable_options" id="repl_environment_variable_options">#</a></span></h2>
<p>The built-in repl (invoked by running <code>node</code> or <code>node -i</code>) may be controlled
via the following environment variables:</p>
<ul>
<li><code>NODE_REPL_HISTORY</code> - When a valid path is given, persistent REPL history
will be saved to the specified file rather than <code>.node_repl_history</code> in the
user's home directory. Setting this value to <code>""</code> will disable persistent
REPL history. Whitespace will be trimmed from the value.</li>
<li><code>NODE_REPL_HISTORY_SIZE</code> - Defaults to <code>1000</code>. Controls how many lines of
history will be persisted if history is available. Must be a positive number.</li>
<li><code>NODE_REPL_MODE</code> - May be any of <code>sloppy</code>, <code>strict</code>, or <code>magic</code>. Defaults
to <code>magic</code>, which will automatically run "strict mode only" statements in
strict mode.</li>
</ul>
<h2>Persistent History<span><a class="mark" href="#repl_persistent_history" id="repl_persistent_history">#</a></span></h2>
<p>By default, the REPL will persist history between <code>node</code> REPL sessions by saving
to a <code>.node_repl_history</code> file in the user's home directory. This can be
disabled by setting the environment variable <code>NODE_REPL_HISTORY=""</code>.</p>
<h3>NODE_REPL_HISTORY_FILE<span><a class="mark" href="#repl_node_repl_history_file" id="repl_node_repl_history_file">#</a></span></h3>
<pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <code>NODE_REPL_HISTORY</code> instead.</pre><p>Previously in Node.js/io.js v2.x, REPL history was controlled by using a
<code>NODE_REPL_HISTORY_FILE</code> environment variable, and the history was saved in JSON
format. This variable has now been deprecated, and your REPL history will
automatically be converted to using plain text. The new file will be saved to
either your home directory, or a directory defined by the <code>NODE_REPL_HISTORY</code>
variable, as documented <a href="#repl_environment_variable_options">here</a>.</p>
<h2>REPL Features<span><a class="mark" href="#repl_repl_features" id="repl_repl_features">#</a></span></h2>
<!-- type=misc -->
<p>Inside the REPL, Control+D will exit. Multi-line expressions can be input.
Tab completion is supported for both global and local variables.</p>
<p>Core modules will be loaded on-demand into the environment. For example,
accessing <code>fs</code> will <code>require()</code> the <code>fs</code> module as <code>global.fs</code>.</p>
<p>The special variable <code>_</code> (underscore) contains the result of the last expression.</p>
<pre><code>> [ 'a', 'b', 'c' ]
[ 'a', 'b', 'c' ]
> _.length
3
> _ += 1
4
</code></pre><p>The REPL provides access to any variables in the global scope. You can expose
a variable to the REPL explicitly by assigning it to the <code>context</code> object
associated with each <code>REPLServer</code>. For example:</p>
<pre><code class="lang-js">// repl_test.js
const repl = require('repl');
var msg = 'message';
repl.start('> ').context.m = msg;
</code></pre>
<p>Things in the <code>context</code> object appear as local within the REPL:</p>
<pre><code>$ node repl_test.js
> m
'message'
</code></pre><p>There are a few special REPL commands:</p>
<ul>
<li><code>.break</code> - While inputting a multi-line expression, sometimes you get lost
or just don't care about completing it. <code>.break</code> will start over.</li>
<li><code>.clear</code> - Resets the <code>context</code> object to an empty object and clears any
multi-line expression.</li>
<li><code>.exit</code> - Close the I/O stream, which will cause the REPL to exit.</li>
<li><code>.help</code> - Show this list of special commands.</li>
<li><code>.save</code> - Save the current REPL session to a file
.save ./file/to/save.js</li>
<li><code>.load</code> - Load a file into the current REPL session.
.load ./file/to/load.js</li>
</ul>
<p>The following key combinations in the REPL have these special effects:</p>
<ul>
<li><code><ctrl>C</code> - Similar to the <code>.break</code> keyword. Terminates the current
command. Press twice on a blank line to forcibly exit.</li>
<li><code><ctrl>D</code> - Similar to the <code>.exit</code> keyword.</li>
<li><code><tab></code> - Show both global and local(scope) variables</li>
</ul>
<h3>Customizing Object displays in the REPL<span><a class="mark" href="#repl_customizing_object_displays_in_the_repl" id="repl_customizing_object_displays_in_the_repl">#</a></span></h3>
<p>The REPL module internally uses
<a href="util.html#util_util_inspect_object_options"><code>util.inspect()</code></a>, when printing values. However, <code>util.inspect</code> delegates the
call to the object's <code>inspect()</code> function, if it has one. You can read more
about this delegation <a href="https://github.com/thlorenz/v8-flags/blob/master/flags-0.11.md">here</a>.</p>
<p>For example, if you have defined an <code>inspect()</code> function on an object, like this:</p>
<pre><code>> var obj = {foo: 'this will not show up in the inspect() output'};
undefined
> obj.inspect = () => {
... return {bar: 'baz'};
... };
[Function]
</code></pre><p>and try to print <code>obj</code> in REPL, it will invoke the custom <code>inspect()</code> function:</p>
<pre><code>> obj
{bar: 'baz'}
</code></pre><h2>Class: REPLServer<span><a class="mark" href="#repl_class_replserver" id="repl_class_replserver">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.91</span>
</div><p>This inherits from <a href="readline.html#readline_class_interface">Readline Interface</a> with the following events:</p>
<h3>Event: 'exit'<span><a class="mark" href="#repl_event_exit" id="repl_event_exit">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p><code>function () {}</code></p>
<p>Emitted when the user exits the REPL in any of the defined ways. Namely, typing
<code>.exit</code> at the repl, pressing Ctrl+C twice to signal <code>SIGINT</code>, or pressing Ctrl+D
to signal <code>'end'</code> on the <code>input</code> stream.</p>
<p>Example of listening for <code>exit</code>:</p>
<pre><code class="lang-js">replServer.on('exit', () => {
console.log('Got "exit" event from repl!');
process.exit();
});
</code></pre>
<h3>Event: 'reset'<span><a class="mark" href="#repl_event_reset" id="repl_event_reset">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.0</span>
</div><p><code>function (context) {}</code></p>
<p>Emitted when the REPL's context is reset. This happens when you type <code>.clear</code>.
If you start the repl with <code>{ useGlobal: true }</code> then this event will never
be emitted.</p>
<p>Example of listening for <code>reset</code>:</p>
<pre><code class="lang-js">// Extend the initial repl context.
var replServer = repl.start({ options ... });
someExtension.extend(r.context);
// When a new context is created extend it as well.
replServer.on('reset', (context) => {
console.log('repl has a new context');
someExtension.extend(context);
});
</code></pre>
<h3>replServer.defineCommand(keyword, cmd)<span><a class="mark" href="#repl_replserver_definecommand_keyword_cmd" id="repl_replserver_definecommand_keyword_cmd">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><ul>
<li><code>keyword</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a></li>
<li><code>cmd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Makes a command available in the REPL. The command is invoked by typing a <code>.</code>
followed by the keyword. The <code>cmd</code> is an object with the following values:</p>
<ul>
<li><code>help</code> - help text to be displayed when <code>.help</code> is entered (Optional).</li>
<li><code>action</code> - a function to execute, potentially taking in a string argument,
when the command is invoked, bound to the REPLServer instance (Required).</li>
</ul>
<p>If a function is provided instead of an object for <code>cmd</code>, it is treated as the
<code>action</code>.</p>
<p>Example of defining a command:</p>
<pre><code class="lang-js">// repl_test.js
const repl = require('repl');
var replServer = repl.start();
replServer.defineCommand('sayhello', {
help: 'Say hello',
action: function(name) {
this.write(`Hello, ${name}!\n`);
this.displayPrompt();
}
});
</code></pre>
<p>Example of invoking that command from the REPL:</p>
<pre><code>> .sayhello Node.js User
Hello, Node.js User!
</code></pre><h3>replServer.displayPrompt([preserveCursor])<span><a class="mark" href="#repl_replserver_displayprompt_preservecursor" id="repl_replserver_displayprompt_preservecursor">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.91</span>
</div><ul>
<li><code>preserveCursor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
<p>Like <a href="readline.html#readline_rl_prompt_preservecursor"><code>readline.prompt</code></a> except also adding indents with ellipses when inside
blocks. The <code>preserveCursor</code> argument is passed to <a href="readline.html#readline_rl_prompt_preservecursor"><code>readline.prompt</code></a>. This is
used primarily with <code>defineCommand</code>. It's also used internally to render each
prompt line.</p>
<h2>repl.start(options)<span><a class="mark" href="#repl_repl_start_options" id="repl_repl_start_options">#</a></span></h2>
<p>Returns and starts a <code>REPLServer</code> instance, that inherits from
<a href="readline.html#readline_class_interface">Readline Interface</a>. Accepts an "options" Object that takes
the following values:</p>
<ul>
<li><p><code>prompt</code> - the prompt and <code>stream</code> for all I/O. Defaults to <code>></code>.</p>
</li>
<li><p><code>input</code> - the readable stream to listen to. Defaults to <code>process.stdin</code>.</p>
</li>
<li><p><code>output</code> - the writable stream to write readline data to. Defaults to
<code>process.stdout</code>.</p>
</li>
<li><p><code>terminal</code> - pass <code>true</code> if the <code>stream</code> should be treated like a TTY, and
have ANSI/VT100 escape codes written to it. Defaults to checking <code>isTTY</code>
on the <code>output</code> stream upon instantiation.</p>
</li>
<li><p><code>eval</code> - function that will be used to eval each given line. Defaults to
an async wrapper for <code>eval()</code>. See below for an example of a custom <code>eval</code>.</p>
</li>
<li><p><code>useColors</code> - a boolean which specifies whether or not the <code>writer</code> function
should output colors. If a different <code>writer</code> function is set then this does
nothing. Defaults to the repl's <code>terminal</code> value.</p>
</li>
<li><p><code>useGlobal</code> - if set to <code>true</code>, then the repl will use the <code>global</code> object,
instead of running scripts in a separate context. Defaults to <code>false</code>.</p>
</li>
<li><p><code>ignoreUndefined</code> - if set to <code>true</code>, then the repl will not output the
return value of command if it's <code>undefined</code>. Defaults to <code>false</code>.</p>
</li>
<li><p><code>writer</code> - the function to invoke for each command that gets evaluated which
returns the formatting (including coloring) to display. Defaults to
<code>util.inspect</code>.</p>
</li>
<li><p><code>replMode</code> - controls whether the repl runs all commands in strict mode,
default mode, or a hybrid mode ("magic" mode.) Acceptable values are:</p>
<ul>
<li><code>repl.REPL_MODE_SLOPPY</code> - run commands in sloppy mode.</li>
<li><code>repl.REPL_MODE_STRICT</code> - run commands in strict mode. This is equivalent to
prefacing every repl statement with <code>'use strict'</code>.</li>
<li><code>repl.REPL_MODE_MAGIC</code> - attempt to run commands in default mode. If they
fail to parse, re-try in strict mode.</li>
</ul>
</li>
</ul>
<p>You can use your own <code>eval</code> function if it has following signature:</p>
<pre><code>function eval(cmd, context, filename, callback) {
callback(null, result);
}
</code></pre><p>On tab completion, <code>eval</code> will be called with <code>.scope</code> as an input string. It
is expected to return an array of scope names to be used for the auto-completion.</p>
<p>Multiple REPLs may be started against the same running instance of Node.js. Each
will share the same global object but will have unique I/O.</p>
<p>Here is an example that starts a REPL on stdin, a Unix socket, and a TCP socket:</p>
<pre><code class="lang-js">const net = require('net');
const repl = require('repl');
var connections = 0;
repl.start({
prompt: 'Node.js via stdin> ',
input: process.stdin,
output: process.stdout
});
net.createServer((socket) => {
connections += 1;
repl.start({
prompt: 'Node.js via Unix socket> ',
input: socket,
output: socket
}).on('exit', () => {
socket.end();
})
}).listen('/tmp/node-repl-sock');
net.createServer((socket) => {
connections += 1;
repl.start({
prompt: 'Node.js via TCP socket> ',
input: socket,
output: socket
}).on('exit', () => {
socket.end();
});
}).listen(5001);
</code></pre>
<p>Running this program from the command line will start a REPL on stdin. Other
REPL clients may connect through the Unix socket or TCP socket. <code>telnet</code> is useful
for connecting to TCP sockets, and <code>socat</code> can be used to connect to both Unix and
TCP sockets.</p>
<p>By starting a REPL from a Unix socket-based server instead of stdin, you can
connect to a long-running Node.js process without restarting it.</p>
<p>For an example of running a "full-featured" (<code>terminal</code>) REPL over
a <code>net.Server</code> and <code>net.Socket</code> instance, see: <a href="https://gist.github.com/2209310">https://gist.github.com/2209310</a></p>
<p>For an example of running a REPL instance over <a href="http://man7.org/linux/man-pages/man1/curl.1.html">curl(1)</a>,
see: <a href="https://gist.github.com/2053342">https://gist.github.com/2053342</a></p>
<!-- [end-include:repl.md] -->
<!-- [start-include:stream.md] -->
<h1>Stream<span><a class="mark" href="#stream_stream" id="stream_stream">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>A stream is an abstract interface implemented by various objects in
Node.js. For example a <a href="http.html#http_class_http_incomingmessage">request to an HTTP server</a> is a
stream, as is <a href="process.html#process_process_stdout"><code>process.stdout</code></a>. Streams are readable, writable, or both. All
streams are instances of <a href="events.html#events_class_eventemitter"><code>EventEmitter</code></a>.</p>
<p>You can load the Stream base classes by doing <code>require('stream')</code>.
There are base classes provided for <a href="#stream_class_stream_readable">Readable</a> streams, <a href="#stream_class_stream_writable">Writable</a>
streams, <a href="#stream_class_stream_duplex">Duplex</a> streams, and <a href="#stream_class_stream_transform">Transform</a> streams.</p>
<p>This document is split up into 3 sections:</p>
<ol>
<li>The first section explains the parts of the API that you need to be
aware of to use streams in your programs.</li>
<li>The second section explains the parts of the API that you need to
use if you implement your own custom streams yourself. The API is designed to
make this easy for you to do.</li>
<li>The third section goes into more depth about how streams work,
including some of the internal mechanisms and functions that you
should probably not modify unless you definitely know what you are
doing.</li>
</ol>
<h2>API for Stream Consumers<span><a class="mark" href="#stream_api_for_stream_consumers" id="stream_api_for_stream_consumers">#</a></span></h2>
<!--type=misc-->
<p>Streams can be either <a href="#stream_class_stream_readable">Readable</a>, <a href="#stream_class_stream_writable">Writable</a>, or both (<a href="#stream_class_stream_duplex">Duplex</a>).</p>
<p>All streams are EventEmitters, but they also have other custom methods
and properties depending on whether they are Readable, Writable, or
Duplex.</p>
<p>If a stream is both Readable and Writable, then it implements all of
the methods and events. So, a <a href="#stream_class_stream_duplex">Duplex</a> or <a href="#stream_class_stream_transform">Transform</a> stream is
fully described by this API, though their implementation may be
somewhat different.</p>
<p>It is not necessary to implement Stream interfaces in order to consume
streams in your programs. If you <strong>are</strong> implementing streaming
interfaces in your own program, please also refer to
<a href="#stream_api_for_stream_implementors">API for Stream Implementors</a>.</p>
<p>Almost all Node.js programs, no matter how simple, use Streams in some
way. Here is an example of using Streams in an Node.js program:</p>
<pre><code class="lang-js">const http = require('http');
var server = http.createServer( (req, res) => {
// req is an http.IncomingMessage, which is a Readable Stream
// res is an http.ServerResponse, which is a Writable Stream
var body = '';
// we want to get the data as utf8 strings
// If you don't set an encoding, then you'll get Buffer objects
req.setEncoding('utf8');
// Readable streams emit 'data' events once a listener is added
req.on('data', (chunk) => {
body += chunk;
});
// the end event tells you that you have entire body
req.on('end', () => {
try {
const data = JSON.parse(body);
// write back something interesting to the user:
res.write(typeof data);
res.end();
} catch (er) {
// uh oh! bad json!
res.statusCode = 400;
return res.end(`error: ${er.message}`);
}
});
});
server.listen(1337);
// $ curl localhost:1337 -d '{}'
// object
// $ curl localhost:1337 -d '"foo"'
// string
// $ curl localhost:1337 -d 'not json'
// error: Unexpected token o
</code></pre>
<h3>Class: stream.Duplex<span><a class="mark" href="#stream_class_stream_duplex" id="stream_class_stream_duplex">#</a></span></h3>
<p>Duplex streams are streams that implement both the <a href="#stream_class_stream_readable">Readable</a> and
<a href="#stream_class_stream_writable">Writable</a> interfaces.</p>
<p>Examples of Duplex streams include:</p>
<ul>
<li><a href="net.html#net_class_net_socket">TCP sockets</a></li>
<li><a href="zlib.html">zlib streams</a></li>
<li><a href="crypto.html">crypto streams</a></li>
</ul>
<h3>Class: stream.Readable<span><a class="mark" href="#stream_class_stream_readable" id="stream_class_stream_readable">#</a></span></h3>
<!--type=class-->
<p>The Readable stream interface is the abstraction for a <em>source</em> of
data that you are reading from. In other words, data comes <em>out</em> of a
Readable stream.</p>
<p>A Readable stream will not start emitting data until you indicate that
you are ready to receive it.</p>
<p>Readable streams have two "modes": a <strong>flowing mode</strong> and a <strong>paused
mode</strong>. When in flowing mode, data is read from the underlying system
and provided to your program as fast as possible. In paused mode, you
must explicitly call <a href="#stream_readable_read_size"><code>stream.read()</code></a> to get chunks of data out.
Streams start out in paused mode.</p>
<p><strong>Note</strong>: If no data event handlers are attached, and there are no
<a href="#stream_readable_pipe_destination_options"><code>stream.pipe()</code></a> destinations, and the stream is switched into flowing
mode, then data will be lost.</p>
<p>You can switch to flowing mode by doing any of the following:</p>
<ul>
<li>Adding a <a href="#stream_event_data"><code>'data'</code></a> event handler to listen for data.</li>
<li>Calling the <a href="#stream_readable_resume"><code>stream.resume()</code></a> method to explicitly open the
flow.</li>
<li>Calling the <a href="#stream_readable_pipe_destination_options"><code>stream.pipe()</code></a> method to send the data to a <a href="#stream_class_stream_writable">Writable</a>.</li>
</ul>
<p>You can switch back to paused mode by doing either of the following:</p>
<ul>
<li>If there are no pipe destinations, by calling the
<a href="#stream_readable_pause"><code>stream.pause()</code></a> method.</li>
<li>If there are pipe destinations, by removing any <a href="#stream_event_data"><code>'data'</code></a> event
handlers, and removing all pipe destinations by calling the
<a href="#stream_readable_unpipe_destination"><code>stream.unpipe()</code></a> method.</li>
</ul>
<p>Note that, for backwards compatibility reasons, removing <a href="#stream_event_data"><code>'data'</code></a>
event handlers will <strong>not</strong> automatically pause the stream. Also, if
there are piped destinations, then calling <a href="#stream_readable_pause"><code>stream.pause()</code></a> will
not guarantee that the stream will <em>remain</em> paused once those
destinations drain and ask for more data.</p>
<p>Examples of readable streams include:</p>
<ul>
<li><a href="http.html#http_class_http_incomingmessage">HTTP responses, on the client</a></li>
<li><a href="http.html#http_class_http_incomingmessage">HTTP requests, on the server</a></li>
<li><a href="fs.html#fs_class_fs_readstream">fs read streams</a></li>
<li><a href="zlib.html">zlib streams</a></li>
<li><a href="crypto.html">crypto streams</a></li>
<li><a href="net.html#net_class_net_socket">TCP sockets</a></li>
<li><a href="child_process.html#child_process_child_stdout">child process stdout and stderr</a></li>
<li><a href="process.html#process_process_stdin"><code>process.stdin</code></a></li>
</ul>
<h4>Event: 'close'<span><a class="mark" href="#stream_event_close" id="stream_event_close">#</a></span></h4>
<p>Emitted when the stream and any of its underlying resources (a file
descriptor, for example) have been closed. The event indicates that
no more events will be emitted, and no further computation will occur.</p>
<p>Not all streams will emit the <code>'close'</code> event as the <code>'close'</code> event is
optional.</p>
<h4>Event: 'data'<span><a class="mark" href="#stream_event_data" id="stream_event_data">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The chunk of data.</li>
</ul>
</div><p>Attaching a <code>'data'</code> event listener to a stream that has not been
explicitly paused will switch the stream into flowing mode. Data will
then be passed as soon as it is available.</p>
<p>If you just want to get all the data out of the stream as fast as
possible, this is the best way to do so.</p>
<pre><code class="lang-js">var readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log('got %d bytes of data', chunk.length);
});
</code></pre>
<h4>Event: 'end'<span><a class="mark" href="#stream_event_end" id="stream_event_end">#</a></span></h4>
<p>This event fires when there will be no more data to read.</p>
<p>Note that the <code>'end'</code> event <strong>will not fire</strong> unless the data is
completely consumed. This can be done by switching into flowing mode,
or by calling <a href="#stream_readable_read_size"><code>stream.read()</code></a> repeatedly until you get to the
end.</p>
<pre><code class="lang-js">var readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log('got %d bytes of data', chunk.length);
});
readable.on('end', () => {
console.log('there will be no more data.');
});
</code></pre>
<h4>Event: 'error'<span><a class="mark" href="#stream_event_error" id="stream_event_error">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
</div><p>Emitted if there was an error receiving data.</p>
<h4>Event: 'readable'<span><a class="mark" href="#stream_event_readable" id="stream_event_readable">#</a></span></h4>
<p>When a chunk of data can be read from the stream, it will emit a
<code>'readable'</code> event.</p>
<p>In some cases, listening for a <code>'readable'</code> event will cause some data
to be read into the internal buffer from the underlying system, if it
hadn't already.</p>
<pre><code class="lang-javascript">var readable = getReadableStreamSomehow();
readable.on('readable', () => {
// there is some data to read now
});
</code></pre>
<p>Once the internal buffer is drained, a <code>'readable'</code> event will fire
again when more data is available.</p>
<p>The <code>'readable'</code> event is not emitted in the "flowing" mode with the
sole exception of the last one, on end-of-stream.</p>
<p>The <code>'readable'</code> event indicates that the stream has new information:
either new data is available or the end of the stream has been reached.
In the former case, <a href="#stream_readable_read_size"><code>stream.read()</code></a> will return that data. In the
latter case, <a href="#stream_readable_read_size"><code>stream.read()</code></a> will return null. For instance, in
the following example, <code>foo.txt</code> is an empty file:</p>
<pre><code class="lang-js">const fs = require('fs');
var rr = fs.createReadStream('foo.txt');
rr.on('readable', () => {
console.log('readable:', rr.read());
});
rr.on('end', () => {
console.log('end');
});
</code></pre>
<p>The output of running this script is:</p>
<pre><code>$ node test.js
readable: null
end
</code></pre><h4>readable.isPaused()<span><a class="mark" href="#stream_readable_ispaused" id="stream_readable_ispaused">#</a></span></h4>
<div class="signature"><ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a></li>
</ul>
</div><p>This method returns whether or not the <code>readable</code> has been <strong>explicitly</strong>
paused by client code (using <a href="#stream_readable_pause"><code>stream.pause()</code></a> without a
corresponding <a href="#stream_readable_resume"><code>stream.resume()</code></a>).</p>
<pre><code class="lang-js">var readable = new stream.Readable
readable.isPaused() // === false
readable.pause()
readable.isPaused() // === true
readable.resume()
readable.isPaused() // === false
</code></pre>
<h4>readable.pause()<span><a class="mark" href="#stream_readable_pause" id="stream_readable_pause">#</a></span></h4>
<div class="signature"><ul>
<li>Returns: <code>this</code></li>
</ul>
</div><p>This method will cause a stream in flowing mode to stop emitting
<a href="#stream_event_data"><code>'data'</code></a> events, switching out of flowing mode. Any data that becomes
available will remain in the internal buffer.</p>
<pre><code class="lang-js">var readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log('got %d bytes of data', chunk.length);
readable.pause();
console.log('there will be no more data for 1 second');
setTimeout(() => {
console.log('now data will start flowing again');
readable.resume();
}, 1000);
});
</code></pre>
<h4>readable.pipe(destination[, options])<span><a class="mark" href="#stream_readable_pipe_destination_options" id="stream_readable_pipe_destination_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>destination</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a> The destination for writing data</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Pipe options<ul>
<li><code>end</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> End the writer when the reader ends. Default = <code>true</code></li>
</ul>
</li>
</ul>
</div><p>This method pulls all the data out of a readable stream, and writes it
to the supplied destination, automatically managing the flow so that
the destination is not overwhelmed by a fast readable stream.</p>
<p>Multiple destinations can be piped to safely.</p>
<pre><code class="lang-js">var readable = getReadableStreamSomehow();
var writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt'
readable.pipe(writable);
</code></pre>
<p>This function returns the destination stream, so you can set up pipe
chains like so:</p>
<pre><code class="lang-js">var r = fs.createReadStream('file.txt');
var z = zlib.createGzip();
var w = fs.createWriteStream('file.txt.gz');
r.pipe(z).pipe(w);
</code></pre>
<p>For example, emulating the Unix <code>cat</code> command:</p>
<pre><code class="lang-js">process.stdin.pipe(process.stdout);
</code></pre>
<p>By default <a href="#stream_writable_end_chunk_encoding_callback"><code>stream.end()</code></a> is called on the destination when the
source stream emits <a href="#stream_event_end"><code>'end'</code></a>, so that <code>destination</code> is no longer writable.
Pass <code>{ end: false }</code> as <code>options</code> to keep the destination stream open.</p>
<p>This keeps <code>writer</code> open so that "Goodbye" can be written at the
end.</p>
<pre><code class="lang-js">reader.pipe(writer, { end: false });
reader.on('end', () => {
writer.end('Goodbye\n');
});
</code></pre>
<p>Note that <a href="process.html#process_process_stderr"><code>process.stderr</code></a> and <a href="process.html#process_process_stdout"><code>process.stdout</code></a> are never closed until
the process exits, regardless of the specified options.</p>
<h4>readable.read([size])<span><a class="mark" href="#stream_readable_read_size" id="stream_readable_read_size">#</a></span></h4>
<div class="signature"><ul>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Optional argument to specify how much data to read.</li>
<li>Return <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><Null></a></li>
</ul>
</div><p>The <code>read()</code> method pulls some data out of the internal buffer and
returns it. If there is no data available, then it will return
<code>null</code>.</p>
<p>If you pass in a <code>size</code> argument, then it will return that many
bytes. If <code>size</code> bytes are not available, then it will return <code>null</code>,
unless we've ended, in which case it will return the data remaining
in the buffer.</p>
<p>If you do not specify a <code>size</code> argument, then it will return all the
data in the internal buffer.</p>
<p>This method should only be called in paused mode. In flowing mode,
this method is called automatically until the internal buffer is
drained.</p>
<pre><code class="lang-js">var readable = getReadableStreamSomehow();
readable.on('readable', () => {
var chunk;
while (null !== (chunk = readable.read())) {
console.log('got %d bytes of data', chunk.length);
}
});
</code></pre>
<p>If this method returns a data chunk, then it will also trigger the
emission of a <a href="#stream_event_data"><code>'data'</code></a> event.</p>
<p>Note that calling <a href="#stream_readable_read_size"><code>stream.read([size])</code></a> after the <a href="#stream_event_end"><code>'end'</code></a>
event has been triggered will return <code>null</code>. No runtime error will be raised.</p>
<h4>readable.resume()<span><a class="mark" href="#stream_readable_resume" id="stream_readable_resume">#</a></span></h4>
<div class="signature"><ul>
<li>Returns: <code>this</code></li>
</ul>
</div><p>This method will cause the readable stream to resume emitting <a href="#stream_event_data"><code>'data'</code></a>
events.</p>
<p>This method will switch the stream into flowing mode. If you do <em>not</em>
want to consume the data from a stream, but you <em>do</em> want to get to
its <a href="#stream_event_end"><code>'end'</code></a> event, you can call <a href="#stream_readable_resume"><code>stream.resume()</code></a> to open
the flow of data.</p>
<pre><code class="lang-js">var readable = getReadableStreamSomehow();
readable.resume();
readable.on('end', () => {
console.log('got to the end, but did not read anything');
});
</code></pre>
<h4>readable.setEncoding(encoding)<span><a class="mark" href="#stream_readable_setencoding_encoding" id="stream_readable_setencoding_encoding">#</a></span></h4>
<div class="signature"><ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The encoding to use.</li>
<li>Returns: <code>this</code></li>
</ul>
</div><p>Call this function to cause the stream to return strings of the specified
encoding instead of Buffer objects. For example, if you do
<code>readable.setEncoding('utf8')</code>, then the output data will be interpreted as
UTF-8 data, and returned as strings. If you do <code>readable.setEncoding('hex')</code>,
then the data will be encoded in hexadecimal string format.</p>
<p>This properly handles multi-byte characters that would otherwise be
potentially mangled if you simply pulled the Buffers directly and
called <a href="buffer.html#buffer_buf_tostring_encoding_start_end"><code>buf.toString(encoding)</code></a> on them. If you want to read the data
as strings, always use this method.</p>
<p>Also you can disable any encoding at all with <code>readable.setEncoding(null)</code>.
This approach is very useful if you deal with binary data or with large
multi-byte strings spread out over multiple chunks.</p>
<pre><code class="lang-js">var readable = getReadableStreamSomehow();
readable.setEncoding('utf8');
readable.on('data', (chunk) => {
assert.equal(typeof chunk, 'string');
console.log('got %d characters of string data', chunk.length);
});
</code></pre>
<h4>readable.unpipe([destination])<span><a class="mark" href="#stream_readable_unpipe_destination" id="stream_readable_unpipe_destination">#</a></span></h4>
<div class="signature"><ul>
<li><code>destination</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a> Optional specific stream to unpipe</li>
</ul>
</div><p>This method will remove the hooks set up for a previous <a href="#stream_readable_pipe_destination_options"><code>stream.pipe()</code></a>
call.</p>
<p>If the destination is not specified, then all pipes are removed.</p>
<p>If the destination is specified, but no pipe is set up for it, then
this is a no-op.</p>
<pre><code class="lang-js">var readable = getReadableStreamSomehow();
var writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt',
// but only for the first second
readable.pipe(writable);
setTimeout(() => {
console.log('stop writing to file.txt');
readable.unpipe(writable);
console.log('manually close the file stream');
writable.end();
}, 1000);
</code></pre>
<h4>readable.unshift(chunk)<span><a class="mark" href="#stream_readable_unshift_chunk" id="stream_readable_unshift_chunk">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Chunk of data to unshift onto the read queue</li>
</ul>
</div><p>This is useful in certain cases where a stream is being consumed by a
parser, which needs to "un-consume" some data that it has
optimistically pulled out of the source, so that the stream can be
passed on to some other party.</p>
<p>Note that <code>stream.unshift(chunk)</code> cannot be called after the <a href="#stream_event_end"><code>'end'</code></a> event
has been triggered; a runtime error will be raised.</p>
<p>If you find that you must often call <code>stream.unshift(chunk)</code> in your
programs, consider implementing a <a href="#stream_class_stream_transform">Transform</a> stream instead. (See <a href="#stream_api_for_stream_implementors">API
for Stream Implementors</a>.)</p>
<pre><code class="lang-js">// Pull off a header delimited by \n\n
// use unshift() if we get too much
// Call the callback with (error, header, stream)
const StringDecoder = require('string_decoder').StringDecoder;
function parseHeader(stream, callback) {
stream.on('error', callback);
stream.on('readable', onReadable);
var decoder = new StringDecoder('utf8');
var header = '';
function onReadable() {
var chunk;
while (null !== (chunk = stream.read())) {
var str = decoder.write(chunk);
if (str.match(/\n\n/)) {
// found the header boundary
var split = str.split(/\n\n/);
header += split.shift();
var remaining = split.join('\n\n');
var buf = new Buffer(remaining, 'utf8');
if (buf.length)
stream.unshift(buf);
stream.removeListener('error', callback);
stream.removeListener('readable', onReadable);
// now the body of the message can be read from the stream.
callback(null, header, stream);
} else {
// still reading the header.
header += str;
}
}
}
}
</code></pre>
<p>Note that, unlike <a href="#stream_readable_push_chunk_encoding"><code>stream.push(chunk)</code></a>, <code>stream.unshift(chunk)</code>
will not end the reading process by resetting the internal reading state of the
stream. This can cause unexpected results if <code>unshift()</code> is called during a
read (i.e. from within a <a href="#stream_readable_read_size_1"><code>stream._read()</code></a> implementation on a
custom stream). Following the call to <code>unshift()</code> with an immediate
<a href="#stream_readable_push_chunk_encoding"><code>stream.push('')</code></a> will reset the reading state appropriately,
however it is best to simply avoid calling <code>unshift()</code> while in the process of
performing a read.</p>
<h4>readable.wrap(stream)<span><a class="mark" href="#stream_readable_wrap_stream" id="stream_readable_wrap_stream">#</a></span></h4>
<div class="signature"><ul>
<li><code>stream</code> <a href="stream.html#stream_stream" class="type"><Stream></a> An "old style" readable stream</li>
</ul>
</div><p>Versions of Node.js prior to v0.10 had streams that did not implement the
entire Streams API as it is today. (See <a href="#stream_compatibility_with_older_node_js_versions">Compatibility</a> for
more information.)</p>
<p>If you are using an older Node.js library that emits <a href="#stream_event_data"><code>'data'</code></a> events and
has a <a href="#stream_readable_pause"><code>stream.pause()</code></a> method that is advisory only, then you
can use the <code>wrap()</code> method to create a <a href="#stream_class_stream_readable">Readable</a> stream that uses the old
stream as its data source.</p>
<p>You will very rarely ever need to call this function, but it exists
as a convenience for interacting with old Node.js programs and libraries.</p>
<p>For example:</p>
<pre><code class="lang-js">const OldReader = require('./old-api-module.js').OldReader;
const Readable = require('stream').Readable;
const oreader = new OldReader;
const myReader = new Readable().wrap(oreader);
myReader.on('readable', () => {
myReader.read(); // etc.
});
</code></pre>
<h3>Class: stream.Transform<span><a class="mark" href="#stream_class_stream_transform" id="stream_class_stream_transform">#</a></span></h3>
<p>Transform streams are <a href="#stream_class_stream_duplex">Duplex</a> streams where the output is in some way
computed from the input. They implement both the <a href="#stream_class_stream_readable">Readable</a> and
<a href="#stream_class_stream_writable">Writable</a> interfaces.</p>
<p>Examples of Transform streams include:</p>
<ul>
<li><a href="zlib.html">zlib streams</a></li>
<li><a href="crypto.html">crypto streams</a></li>
</ul>
<h3>Class: stream.Writable<span><a class="mark" href="#stream_class_stream_writable" id="stream_class_stream_writable">#</a></span></h3>
<!--type=class-->
<p>The Writable stream interface is an abstraction for a <em>destination</em>
that you are writing data <em>to</em>.</p>
<p>Examples of writable streams include:</p>
<ul>
<li><a href="http.html#http_class_http_clientrequest">HTTP requests, on the client</a></li>
<li><a href="http.html#http_class_http_serverresponse">HTTP responses, on the server</a></li>
<li><a href="fs.html#fs_class_fs_writestream">fs write streams</a></li>
<li><a href="zlib.html">zlib streams</a></li>
<li><a href="crypto.html">crypto streams</a></li>
<li><a href="net.html#net_class_net_socket">TCP sockets</a></li>
<li><a href="child_process.html#child_process_child_stdin">child process stdin</a></li>
<li><a href="process.html#process_process_stdout"><code>process.stdout</code></a>, <a href="process.html#process_process_stderr"><code>process.stderr</code></a></li>
</ul>
<h4>Event: 'close'<span><a class="mark" href="#stream_event_close_1" id="stream_event_close_1">#</a></span></h4>
<p>Emitted when the stream and any of its underlying resources (a file descriptor,
for example) have been closed. The event indicates that no more events will be
emitted, and no further computation will occur.</p>
<p>Not all streams will emit the <code>'close'</code> event as the <code>'close'</code> event is
optional.</p>
<h4>Event: 'drain'<span><a class="mark" href="#stream_event_drain" id="stream_event_drain">#</a></span></h4>
<p>If a <a href="#stream_writable_write_chunk_encoding_callback"><code>stream.write(chunk)</code></a> call returns <code>false</code>, then the
<code>'drain'</code> event will indicate when it is appropriate to begin writing more data
to the stream.</p>
<pre><code class="lang-js">// Write the data to the supplied writable stream one million times.
// Be attentive to back-pressure.
function writeOneMillionTimes(writer, data, encoding, callback) {
var i = 1000000;
write();
function write() {
var ok = true;
do {
i -= 1;
if (i === 0) {
// last time!
writer.write(data, encoding, callback);
} else {
// see if we should continue, or wait
// don't pass the callback, because we're not done yet.
ok = writer.write(data, encoding);
}
} while (i > 0 && ok);
if (i > 0) {
// had to stop early!
// write some more once it drains
writer.once('drain', write);
}
}
}
</code></pre>
<h4>Event: 'error'<span><a class="mark" href="#stream_event_error_1" id="stream_event_error_1">#</a></span></h4>
<div class="signature"><ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
</div><p>Emitted if there was an error when writing or piping data.</p>
<h4>Event: 'finish'<span><a class="mark" href="#stream_event_finish" id="stream_event_finish">#</a></span></h4>
<p>When the <a href="#stream_writable_end_chunk_encoding_callback"><code>stream.end()</code></a> method has been called, and all data has
been flushed to the underlying system, this event is emitted.</p>
<pre><code class="lang-javascript">var writer = getWritableStreamSomehow();
for (var i = 0; i < 100; i ++) {
writer.write('hello, #${i}!\n');
}
writer.end('this is the end\n');
writer.on('finish', () => {
console.error('all writes are now complete.');
});
</code></pre>
<h4>Event: 'pipe'<span><a class="mark" href="#stream_event_pipe" id="stream_event_pipe">#</a></span></h4>
<div class="signature"><ul>
<li><code>src</code> <a href="stream.html#stream_class_stream_readable" class="type"><stream.Readable></a> source stream that is piping to this writable</li>
</ul>
</div><p>This is emitted whenever the <a href="#stream_readable_pipe_destination_options"><code>stream.pipe()</code></a> method is called on a readable
stream, adding this writable to its set of destinations.</p>
<pre><code class="lang-js">var writer = getWritableStreamSomehow();
var reader = getReadableStreamSomehow();
writer.on('pipe', (src) => {
console.error('something is piping into the writer');
assert.equal(src, reader);
});
reader.pipe(writer);
</code></pre>
<h4>Event: 'unpipe'<span><a class="mark" href="#stream_event_unpipe" id="stream_event_unpipe">#</a></span></h4>
<div class="signature"><ul>
<li><code>src</code> <span class="type"><<a href="#stream_class_stream_readable">Readable</a> Stream></span> The source stream that
<a href="#stream_readable_unpipe_destination">unpiped</a> this writable</li>
</ul>
</div><p>This is emitted whenever the <a href="#stream_readable_unpipe_destination"><code>stream.unpipe()</code></a> method is called on a
readable stream, removing this writable from its set of destinations.</p>
<pre><code class="lang-js">var writer = getWritableStreamSomehow();
var reader = getReadableStreamSomehow();
writer.on('unpipe', (src) => {
console.error('something has stopped piping into the writer');
assert.equal(src, reader);
});
reader.pipe(writer);
reader.unpipe(writer);
</code></pre>
<h4>writable.cork()<span><a class="mark" href="#stream_writable_cork" id="stream_writable_cork">#</a></span></h4>
<p>Forces buffering of all writes.</p>
<p>Buffered data will be flushed either at <a href="#stream_writable_uncork"><code>stream.uncork()</code></a> or at
<a href="#stream_writable_end_chunk_encoding_callback"><code>stream.end()</code></a> call.</p>
<h4>writable.end([chunk][, encoding][, callback])<span><a class="mark" href="#stream_writable_end_chunk_encoding_callback" id="stream_writable_end_chunk_encoding_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> Optional data to write</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The encoding, if <code>chunk</code> is a String</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Optional callback for when the stream is finished</li>
</ul>
</div><p>Call this method when no more data will be written to the stream. If supplied,
the callback is attached as a listener on the <a href="#stream_event_finish"><code>'finish'</code></a> event.</p>
<p>Calling <a href="#stream_writable_write_chunk_encoding_callback"><code>stream.write()</code></a> after calling
<a href="#stream_writable_end_chunk_encoding_callback"><code>stream.end()</code></a> will raise an error.</p>
<pre><code class="lang-js">// write 'hello, ' and then end with 'world!'
var file = fs.createWriteStream('example.txt');
file.write('hello, ');
file.end('world!');
// writing more now is not allowed!
</code></pre>
<h4>writable.setDefaultEncoding(encoding)<span><a class="mark" href="#stream_writable_setdefaultencoding_encoding" id="stream_writable_setdefaultencoding_encoding">#</a></span></h4>
<div class="signature"><ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The new default encoding</li>
</ul>
</div><p>Sets the default encoding for a writable stream.</p>
<h4>writable.uncork()<span><a class="mark" href="#stream_writable_uncork" id="stream_writable_uncork">#</a></span></h4>
<p>Flush all data, buffered since <a href="#stream_writable_cork"><code>stream.cork()</code></a> call.</p>
<h4>writable.write(chunk[, encoding][, callback])<span><a class="mark" href="#stream_writable_write_chunk_encoding_callback" id="stream_writable_write_chunk_encoding_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> | <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> The data to write</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The encoding, if <code>chunk</code> is a String</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Callback for when this chunk of data is flushed</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> <code>true</code> if the data was handled completely.</li>
</ul>
</div><p>This method writes some data to the underlying system, and calls the
supplied callback once the data has been fully handled. If an error
occurs, the callback may or may not be called with the error as its
first argument. To detect write errors, listen for the <code>'error'</code> event.</p>
<p>The return value indicates if you should continue writing right now.
If the data had to be buffered internally, then it will return
<code>false</code>. Otherwise, it will return <code>true</code>.</p>
<p>This return value is strictly advisory. You MAY continue to write,
even if it returns <code>false</code>. However, writes will be buffered in
memory, so it is best not to do this excessively. Instead, wait for
the <a href="#stream_event_drain"><code>'drain'</code></a> event before writing more data.</p>
<h2>API for Stream Implementors<span><a class="mark" href="#stream_api_for_stream_implementors" id="stream_api_for_stream_implementors">#</a></span></h2>
<!--type=misc-->
<p>To implement any sort of stream, the pattern is the same:</p>
<ol>
<li>Extend the appropriate parent class in your own subclass. (The
<a href="util.html#util_util_inherits_constructor_superconstructor"><code>util.inherits()</code></a> method is particularly helpful for this.)</li>
<li>Call the appropriate parent class constructor in your constructor,
to be sure that the internal mechanisms are set up properly.</li>
<li>Implement one or more specific methods, as detailed below.</li>
</ol>
<p>The class to extend and the method(s) to implement depend on the sort
of stream class you are writing:</p>
<table>
<thead>
<tr>
<th>
<p>Use-case</p>
</th>
<th>
<p>Class</p>
</th>
<th>
<p>Method(s) to implement</p>
</th>
</tr>
</thead>
<tr>
<td>
<p>Reading only</p>
</td>
<td>
<p><a href="#stream_class_stream_readable_1">Readable</a></p>
</td>
<td>
<p><code><a href="#stream_readable_read_size_1">_read</a></code></p>
</td>
</tr>
<tr>
<td>
<p>Writing only</p>
</td>
<td>
<p><a href="#stream_class_stream_writable_1">Writable</a></p>
</td>
<td>
<p><code><a href="#stream_writable_write_chunk_encoding_callback_1">_write</a></code>, <code><a href="#stream_writable_writev_chunks_callback">_writev</a></code></p>
</td>
</tr>
<tr>
<td>
<p>Reading and writing</p>
</td>
<td>
<p><a href="#stream_class_stream_duplex_1">Duplex</a></p>
</td>
<td>
<p><code><a href="#stream_readable_read_size_1">_read</a></code>, <code><a href="#stream_writable_write_chunk_encoding_callback_1">_write</a></code>, <code><a href="#stream_writable_writev_chunks_callback">_writev</a></code></p>
</td>
</tr>
<tr>
<td>
<p>Operate on written data, then read the result</p>
</td>
<td>
<p><a href="#stream_class_stream_transform_1">Transform</a></p>
</td>
<td>
<p><code><a href="#stream_transform_transform_chunk_encoding_callback">_transform</a></code>, <code><a href="#stream_transform_flush_callback">_flush</a></code></p>
</td>
</tr>
</table>
<p>In your implementation code, it is very important to never call the methods
described in <a href="#stream_api_for_stream_consumers">API for Stream Consumers</a>. Otherwise, you can potentially cause
adverse side effects in programs that consume your streaming interfaces.</p>
<h3>Class: stream.Duplex<span><a class="mark" href="#stream_class_stream_duplex_1" id="stream_class_stream_duplex_1">#</a></span></h3>
<!--type=class-->
<p>A "duplex" stream is one that is both Readable and Writable, such as a TCP
socket connection.</p>
<p>Note that <code>stream.Duplex</code> is an abstract class designed to be extended
with an underlying implementation of the <a href="#stream_readable_read_size_1"><code>stream._read(size)</code></a>
and <a href="#stream_writable_write_chunk_encoding_callback_1"><code>stream._write(chunk, encoding, callback)</code></a> methods as you
would with a Readable or Writable stream class.</p>
<p>Since JavaScript doesn't have multiple prototypal inheritance, this class
prototypally inherits from Readable, and then parasitically from Writable. It is
thus up to the user to implement both the low-level
<a href="#stream_readable_read_size_1"><code>stream._read(n)</code></a> method as well as the low-level
<a href="#stream_writable_write_chunk_encoding_callback_1"><code>stream._write(chunk, encoding, callback)</code></a> method on extension
duplex classes.</p>
<h4>new stream.Duplex(options)<span><a class="mark" href="#stream_new_stream_duplex_options" id="stream_new_stream_duplex_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Passed to both Writable and Readable
constructors. Also has the following fields:<ul>
<li><code>allowHalfOpen</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default = <code>true</code>. If set to <code>false</code>, then
the stream will automatically end the readable side when the
writable side ends and vice versa.</li>
<li><code>readableObjectMode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default = <code>false</code>. Sets <code>objectMode</code>
for readable side of the stream. Has no effect if <code>objectMode</code>
is <code>true</code>.</li>
<li><code>writableObjectMode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Default = <code>false</code>. Sets <code>objectMode</code>
for writable side of the stream. Has no effect if <code>objectMode</code>
is <code>true</code>.</li>
</ul>
</li>
</ul>
</div><p>In classes that extend the Duplex class, make sure to call the
constructor so that the buffering settings can be properly
initialized.</p>
<h3>Class: stream.PassThrough<span><a class="mark" href="#stream_class_stream_passthrough" id="stream_class_stream_passthrough">#</a></span></h3>
<p>This is a trivial implementation of a <a href="#stream_class_stream_transform">Transform</a> stream that simply
passes the input bytes across to the output. Its purpose is mainly
for examples and testing, but there are occasionally use cases where
it can come in handy as a building block for novel sorts of streams.</p>
<h3>Class: stream.Readable<span><a class="mark" href="#stream_class_stream_readable_1" id="stream_class_stream_readable_1">#</a></span></h3>
<!--type=class-->
<p><code>stream.Readable</code> is an abstract class designed to be extended with an
underlying implementation of the <a href="#stream_readable_read_size_1"><code>stream._read(size)</code></a> method.</p>
<p>Please see <a href="#stream_api_for_stream_consumers">API for Stream Consumers</a> for how to consume
streams in your programs. What follows is an explanation of how to
implement Readable streams in your programs.</p>
<h4>new stream.Readable(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#stream_new_stream_readable_options" id="stream_new_stream_readable_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>highWaterMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> The maximum number of bytes to store in
the internal buffer before ceasing to read from the underlying
resource. Default = <code>16384</code> (16kb), or <code>16</code> for <code>objectMode</code> streams</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> If specified, then buffers will be decoded to
strings using the specified encoding. Default = <code>null</code></li>
<li><code>objectMode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Whether this stream should behave
as a stream of objects. Meaning that <a href="#stream_readable_read_size"><code>stream.read(n)</code></a> returns
a single value instead of a Buffer of size n. Default = <code>false</code></li>
<li><code>read</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Implementation for the <a href="#stream_readable_read_size_1"><code>stream._read()</code></a>
method.</li>
</ul>
</li>
</ul>
</div><p>In classes that extend the Readable class, make sure to call the
Readable constructor so that the buffering settings can be properly
initialized.</p>
<h4>readable._read(size)<span><a class="mark" href="#stream_readable_read_size_1" id="stream_readable_read_size_1">#</a></span></h4>
<div class="signature"><ul>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Number of bytes to read asynchronously</li>
</ul>
</div><p>Note: <strong>Implement this method, but do NOT call it directly.</strong></p>
<p>This method is prefixed with an underscore because it is internal to the
class that defines it and should only be called by the internal Readable
class methods. All Readable stream implementations must provide a _read
method to fetch data from the underlying resource.</p>
<p>When <code>_read()</code> is called, if data is available from the resource, the <code>_read()</code>
implementation should start pushing that data into the read queue by calling
<a href="#stream_readable_push_chunk_encoding"><code>this.push(dataChunk)</code></a>. <code>_read()</code> should continue reading from
the resource and pushing data until push returns <code>false</code>, at which point it
should stop reading from the resource. Only when <code>_read()</code> is called again after
it has stopped should it start reading more data from the resource and pushing
that data onto the queue.</p>
<p>Note: once the <code>_read()</code> method is called, it will not be called again until
the <a href="#stream_readable_push_chunk_encoding"><code>stream.push()</code></a> method is called.</p>
<p>The <code>size</code> argument is advisory. Implementations where a "read" is a
single call that returns data can use this to know how much data to
fetch. Implementations where that is not relevant, such as TCP or
TLS, may ignore this argument, and simply provide data whenever it
becomes available. There is no need, for example to "wait" until
<code>size</code> bytes are available before calling <a href="#stream_readable_push_chunk_encoding"><code>stream.push(chunk)</code></a>.</p>
<h4>readable.push(chunk[, encoding])<span><a class="mark" href="#stream_readable_push_chunk_encoding" id="stream_readable_push_chunk_encoding">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><Null></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Chunk of data to push into the read queue</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> Encoding of String chunks. Must be a valid
Buffer encoding, such as <code>'utf8'</code> or <code>'ascii'</code></li>
<li>return <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Whether or not more pushes should be performed</li>
</ul>
</div><p>Note: <strong>This method should be called by Readable implementors, NOT
by consumers of Readable streams.</strong></p>
<p>If a value other than null is passed, The <code>push()</code> method adds a chunk of data
into the queue for subsequent stream processors to consume. If <code>null</code> is
passed, it signals the end of the stream (EOF), after which no more data
can be written.</p>
<p>The data added with <code>push()</code> can be pulled out by calling the
<a href="#stream_readable_read_size"><code>stream.read()</code></a> method when the <a href="#stream_event_readable"><code>'readable'</code></a> event fires.</p>
<p>This API is designed to be as flexible as possible. For example,
you may be wrapping a lower-level source which has some sort of
pause/resume mechanism, and a data callback. In those cases, you
could wrap the low-level source object by doing something like this:</p>
<pre><code class="lang-js">// source is an object with readStop() and readStart() methods,
// and an `ondata` member that gets called when it has data, and
// an `onend` member that gets called when the data is over.
util.inherits(SourceWrapper, Readable);
function SourceWrapper(options) {
Readable.call(this, options);
this._source = getLowlevelSourceObject();
// Every time there's data, we push it into the internal buffer.
this._source.ondata = (chunk) => {
// if push() returns false, then we need to stop reading from source
if (!this.push(chunk))
this._source.readStop();
};
// When the source ends, we push the EOF-signaling `null` chunk
this._source.onend = () => {
this.push(null);
};
}
// _read will be called when the stream wants to pull more data in
// the advisory size argument is ignored in this case.
SourceWrapper.prototype._read = function(size) {
this._source.readStart();
};
</code></pre>
<h4>Example: A Counting Stream<span><a class="mark" href="#stream_example_a_counting_stream" id="stream_example_a_counting_stream">#</a></span></h4>
<!--type=example-->
<p>This is a basic example of a Readable stream. It emits the numerals
from 1 to 1,000,000 in ascending order, and then ends.</p>
<pre><code class="lang-js">const Readable = require('stream').Readable;
const util = require('util');
util.inherits(Counter, Readable);
function Counter(opt) {
Readable.call(this, opt);
this._max = 1000000;
this._index = 1;
}
Counter.prototype._read = function() {
var i = this._index++;
if (i > this._max)
this.push(null);
else {
var str = '' + i;
var buf = new Buffer(str, 'ascii');
this.push(buf);
}
};
</code></pre>
<h4>Example: SimpleProtocol v1 (Sub-optimal)<span><a class="mark" href="#stream_example_simpleprotocol_v1_sub_optimal" id="stream_example_simpleprotocol_v1_sub_optimal">#</a></span></h4>
<p>This is similar to the <code>parseHeader</code> function described
<a href="#stream_readable_unshift_chunk">here</a>, but implemented as a custom stream.
Also, note that this implementation does not convert the incoming data to a
string.</p>
<p>However, this would be better implemented as a <a href="#stream_class_stream_transform">Transform</a> stream. See
<a href="#stream_example_simpleprotocol_parser_v2">SimpleProtocol v2</a> for a better implementation.</p>
<pre><code class="lang-js">// A parser for a simple data protocol.
// The "header" is a JSON object, followed by 2 \n characters, and
// then a message body.
//
// NOTE: This can be done more simply as a Transform stream!
// Using Readable directly for this is sub-optimal. See the
// alternative example below under the Transform section.
const Readable = require('stream').Readable;
const util = require('util');
util.inherits(SimpleProtocol, Readable);
function SimpleProtocol(source, options) {
if (!(this instanceof SimpleProtocol))
return new SimpleProtocol(source, options);
Readable.call(this, options);
this._inBody = false;
this._sawFirstCr = false;
// source is a readable stream, such as a socket or file
this._source = source;
source.on('end', () => {
this.push(null);
});
// give it a kick whenever the source is readable
// read(0) will not consume any bytes
source.on('readable', () => {
this.read(0);
});
this._rawHeader = [];
this.header = null;
}
SimpleProtocol.prototype._read = function(n) {
if (!this._inBody) {
var chunk = this._source.read();
// if the source doesn't have data, we don't have data yet.
if (chunk === null)
return this.push('');
// check if the chunk has a \n\n
var split = -1;
for (var i = 0; i < chunk.length; i++) {
if (chunk[i] === 10) { // '\n'
if (this._sawFirstCr) {
split = i;
break;
} else {
this._sawFirstCr = true;
}
} else {
this._sawFirstCr = false;
}
}
if (split === -1) {
// still waiting for the \n\n
// stash the chunk, and try again.
this._rawHeader.push(chunk);
this.push('');
} else {
this._inBody = true;
var h = chunk.slice(0, split);
this._rawHeader.push(h);
var header = Buffer.concat(this._rawHeader).toString();
try {
this.header = JSON.parse(header);
} catch (er) {
this.emit('error', new Error('invalid simple protocol data'));
return;
}
// now, because we got some extra data, unshift the rest
// back into the read queue so that our consumer will see it.
var b = chunk.slice(split);
this.unshift(b);
// calling unshift by itself does not reset the reading state
// of the stream; since we're inside _read, doing an additional
// push('') will reset the state appropriately.
this.push('');
// and let them know that we are done parsing the header.
this.emit('header', this.header);
}
} else {
// from there on, just provide the data to our consumer.
// careful not to push(null), since that would indicate EOF.
var chunk = this._source.read();
if (chunk) this.push(chunk);
}
};
// Usage:
// var parser = new SimpleProtocol(source);
// Now parser is a readable stream that will emit 'header'
// with the parsed header data.
</code></pre>
<h3>Class: stream.Transform<span><a class="mark" href="#stream_class_stream_transform_1" id="stream_class_stream_transform_1">#</a></span></h3>
<p>A "transform" stream is a duplex stream where the output is causally
connected in some way to the input, such as a <a href="zlib.html">zlib</a> stream or a
<a href="crypto.html">crypto</a> stream.</p>
<p>There is no requirement that the output be the same size as the input,
the same number of chunks, or arrive at the same time. For example, a
Hash stream will only ever have a single chunk of output which is
provided when the input is ended. A zlib stream will produce output
that is either much smaller or much larger than its input.</p>
<p>Rather than implement the <a href="#stream_readable_read_size_1"><code>stream._read()</code></a> and
<a href="#stream_writable_write_chunk_encoding_callback_1"><code>stream._write()</code></a> methods, Transform classes must implement the
<a href="#stream_transform_transform_chunk_encoding_callback"><code>stream._transform()</code></a> method, and may optionally
also implement the <a href="#stream_transform_flush_callback"><code>stream._flush()</code></a> method. (See below.)</p>
<h4>new stream.Transform(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#stream_new_stream_transform_options" id="stream_new_stream_transform_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Passed to both Writable and Readable
constructors. Also has the following fields:<ul>
<li><code>transform</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Implementation for the
<a href="#stream_transform_transform_chunk_encoding_callback"><code>stream._transform()</code></a> method.</li>
<li><code>flush</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Implementation for the <a href="#stream_transform_flush_callback"><code>stream._flush()</code></a>
method.</li>
</ul>
</li>
</ul>
</div><p>In classes that extend the Transform class, make sure to call the
constructor so that the buffering settings can be properly
initialized.</p>
<h4>Events: 'finish' and 'end'<span><a class="mark" href="#stream_events_finish_and_end" id="stream_events_finish_and_end">#</a></span></h4>
<p>The <a href="#stream_event_finish"><code>'finish'</code></a> and <a href="#stream_event_end"><code>'end'</code></a> events are from the parent Writable
and Readable classes respectively. The <code>'finish'</code> event is fired after
<a href="#stream_writable_end_chunk_encoding_callback"><code>stream.end()</code></a> is called and all chunks have been processed by
<a href="#stream_transform_transform_chunk_encoding_callback"><code>stream._transform()</code></a>, <code>'end'</code> is fired after all data has
been output which is after the callback in <a href="#stream_transform_flush_callback"><code>stream._flush()</code></a>
has been called.</p>
<h4>transform._flush(callback)<span><a class="mark" href="#stream_transform_flush_callback" id="stream_transform_flush_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Call this function (optionally with an error
argument) when you are done flushing any remaining data.</li>
</ul>
</div><p>Note: <strong>This function MUST NOT be called directly.</strong> It MAY be implemented
by child classes, and if so, will be called by the internal Transform
class methods only.</p>
<p>In some cases, your transform operation may need to emit a bit more
data at the end of the stream. For example, a <code>Zlib</code> compression
stream will store up some internal state so that it can optimally
compress the output. At the end, however, it needs to do the best it
can with what is left, so that the data will be complete.</p>
<p>In those cases, you can implement a <code>_flush()</code> method, which will be
called at the very end, after all the written data is consumed, but
before emitting <a href="#stream_event_end"><code>'end'</code></a> to signal the end of the readable side. Just
like with <a href="#stream_transform_transform_chunk_encoding_callback"><code>stream._transform()</code></a>, call
<code>transform.push(chunk)</code> zero or more times, as appropriate, and call <code>callback</code>
when the flush operation is complete.</p>
<p>This method is prefixed with an underscore because it is internal to
the class that defines it, and should not be called directly by user
programs. However, you <strong>are</strong> expected to override this method in
your own extension classes.</p>
<h4>transform._transform(chunk, encoding, callback)<span><a class="mark" href="#stream_transform_transform_chunk_encoding_callback" id="stream_transform_transform_chunk_encoding_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The chunk to be transformed. Will <strong>always</strong>
be a buffer unless the <code>decodeStrings</code> option was set to <code>false</code>.</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> If the chunk is a string, then this is the
encoding type. If chunk is a buffer, then this is the special
value - 'buffer', ignore it in this case.</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Call this function (optionally with an error
argument and data) when you are done processing the supplied chunk.</li>
</ul>
</div><p>Note: <strong>This function MUST NOT be called directly.</strong> It should be
implemented by child classes, and called by the internal Transform
class methods only.</p>
<p>All Transform stream implementations must provide a <code>_transform()</code>
method to accept input and produce output.</p>
<p><code>_transform()</code> should do whatever has to be done in this specific
Transform class, to handle the bytes being written, and pass them off
to the readable portion of the interface. Do asynchronous I/O,
process things, and so on.</p>
<p>Call <code>transform.push(outputChunk)</code> 0 or more times to generate output
from this input chunk, depending on how much data you want to output
as a result of this chunk.</p>
<p>Call the callback function only when the current chunk is completely
consumed. Note that there may or may not be output as a result of any
particular input chunk. If you supply a second argument to the callback
it will be passed to the push method. In other words the following are
equivalent:</p>
<pre><code class="lang-js">transform.prototype._transform = function (data, encoding, callback) {
this.push(data);
callback();
};
transform.prototype._transform = function (data, encoding, callback) {
callback(null, data);
};
</code></pre>
<p>This method is prefixed with an underscore because it is internal to
the class that defines it, and should not be called directly by user
programs. However, you <strong>are</strong> expected to override this method in
your own extension classes.</p>
<h4>Example: <code>SimpleProtocol</code> parser v2<span><a class="mark" href="#stream_example_simpleprotocol_parser_v2" id="stream_example_simpleprotocol_parser_v2">#</a></span></h4>
<p>The example <a href="#stream_example_simpleprotocol_v1_sub_optimal">here</a> of a simple
protocol parser can be implemented simply by using the higher level
<a href="#stream_class_stream_transform">Transform</a> stream class, similar to the <code>parseHeader</code> and <code>SimpleProtocol
v1</code> examples.</p>
<p>In this example, rather than providing the input as an argument, it
would be piped into the parser, which is a more idiomatic Node.js stream
approach.</p>
<pre><code class="lang-javascript">const util = require('util');
const Transform = require('stream').Transform;
util.inherits(SimpleProtocol, Transform);
function SimpleProtocol(options) {
if (!(this instanceof SimpleProtocol))
return new SimpleProtocol(options);
Transform.call(this, options);
this._inBody = false;
this._sawFirstCr = false;
this._rawHeader = [];
this.header = null;
}
SimpleProtocol.prototype._transform = function(chunk, encoding, done) {
if (!this._inBody) {
// check if the chunk has a \n\n
var split = -1;
for (var i = 0; i < chunk.length; i++) {
if (chunk[i] === 10) { // '\n'
if (this._sawFirstCr) {
split = i;
break;
} else {
this._sawFirstCr = true;
}
} else {
this._sawFirstCr = false;
}
}
if (split === -1) {
// still waiting for the \n\n
// stash the chunk, and try again.
this._rawHeader.push(chunk);
} else {
this._inBody = true;
var h = chunk.slice(0, split);
this._rawHeader.push(h);
var header = Buffer.concat(this._rawHeader).toString();
try {
this.header = JSON.parse(header);
} catch (er) {
this.emit('error', new Error('invalid simple protocol data'));
return;
}
// and let them know that we are done parsing the header.
this.emit('header', this.header);
// now, because we got some extra data, emit this first.
this.push(chunk.slice(split));
}
} else {
// from there on, just provide the data to our consumer as-is.
this.push(chunk);
}
done();
};
// Usage:
// var parser = new SimpleProtocol();
// source.pipe(parser)
// Now parser is a readable stream that will emit 'header'
// with the parsed header data.
</code></pre>
<h3>Class: stream.Writable<span><a class="mark" href="#stream_class_stream_writable_1" id="stream_class_stream_writable_1">#</a></span></h3>
<!--type=class-->
<p><code>stream.Writable</code> is an abstract class designed to be extended with an
underlying implementation of the
<a href="#stream_writable_write_chunk_encoding_callback_1"><code>stream._write(chunk, encoding, callback)</code></a> method.</p>
<p>Please see <a href="#stream_api_for_stream_consumers">API for Stream Consumers</a> for how to consume
writable streams in your programs. What follows is an explanation of
how to implement Writable streams in your programs.</p>
<h4>new stream.Writable(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#stream_new_stream_writable_options" id="stream_new_stream_writable_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul>
<li><code>highWaterMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><Number></a> Buffer level when
<a href="#stream_writable_write_chunk_encoding_callback"><code>stream.write()</code></a> starts returning <code>false</code>. Default = <code>16384</code>
(16kb), or <code>16</code> for <code>objectMode</code> streams.</li>
<li><code>decodeStrings</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Whether or not to decode strings into
Buffers before passing them to <a href="#stream_writable_write_chunk_encoding_callback_1"><code>stream._write()</code></a>.
Default = <code>true</code></li>
<li><code>objectMode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><Boolean></a> Whether or not the
<a href="#stream_writable_write_chunk_encoding_callback"><code>stream.write(anyObj)</code></a> is a valid operation. If set you can
write arbitrary data instead of only <code>Buffer</code> / <code>String</code> data.
Default = <code>false</code></li>
<li><code>write</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Implementation for the
<a href="#stream_writable_write_chunk_encoding_callback_1"><code>stream._write()</code></a> method.</li>
<li><code>writev</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Implementation for the
<a href="#stream_writable_writev_chunks_callback"><code>stream._writev()</code></a> method.</li>
</ul>
</li>
</ul>
</div><p>In classes that extend the Writable class, make sure to call the
constructor so that the buffering settings can be properly
initialized.</p>
<h4>writable._write(chunk, encoding, callback)<span><a class="mark" href="#stream_writable_write_chunk_encoding_callback_1" id="stream_writable_write_chunk_encoding_callback_1">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <a href="buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The chunk to be written. Will <strong>always</strong>
be a buffer unless the <code>decodeStrings</code> option was set to <code>false</code>.</li>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> If the chunk is a string, then this is the
encoding type. If chunk is a buffer, then this is the special
value - 'buffer', ignore it in this case.</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Call this function (optionally with an error
argument) when you are done processing the supplied chunk.</li>
</ul>
</div><p>All Writable stream implementations must provide a
<a href="#stream_writable_write_chunk_encoding_callback_1"><code>stream._write()</code></a> method to send data to the underlying
resource.</p>
<p>Note: <strong>This function MUST NOT be called directly.</strong> It should be
implemented by child classes, and called by the internal Writable
class methods only.</p>
<p>Call the callback using the standard <code>callback(error)</code> pattern to
signal that the write completed successfully or with an error.</p>
<p>If the <code>decodeStrings</code> flag is set in the constructor options, then
<code>chunk</code> may be a string rather than a Buffer, and <code>encoding</code> will
indicate the sort of string that it is. This is to support
implementations that have an optimized handling for certain string
data encodings. If you do not explicitly set the <code>decodeStrings</code>
option to <code>false</code>, then you can safely ignore the <code>encoding</code> argument,
and assume that <code>chunk</code> will always be a Buffer.</p>
<p>This method is prefixed with an underscore because it is internal to
the class that defines it, and should not be called directly by user
programs. However, you <strong>are</strong> expected to override this method in
your own extension classes.</p>
<h4>writable._writev(chunks, callback)<span><a class="mark" href="#stream_writable_writev_chunks_callback" id="stream_writable_writev_chunks_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunks</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> The chunks to be written. Each chunk has following
format: <code>{ chunk: ..., encoding: ... }</code>.</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Call this function (optionally with an error
argument) when you are done processing the supplied chunks.</li>
</ul>
</div><p>Note: <strong>This function MUST NOT be called directly.</strong> It may be
implemented by child classes, and called by the internal Writable
class methods only.</p>
<p>This function is completely optional to implement. In most cases it is
unnecessary. If implemented, it will be called with all the chunks
that are buffered in the write queue.</p>
<h2>Simplified Constructor API<span><a class="mark" href="#stream_simplified_constructor_api" id="stream_simplified_constructor_api">#</a></span></h2>
<!--type=misc-->
<p>In simple cases there is now the added benefit of being able to construct a
stream without inheritance.</p>
<p>This can be done by passing the appropriate methods as constructor options:</p>
<p>Examples:</p>
<h3>Duplex<span><a class="mark" href="#stream_duplex" id="stream_duplex">#</a></span></h3>
<pre><code class="lang-js">var duplex = new stream.Duplex({
read: function(n) {
// sets this._read under the hood
// push data onto the read queue, passing null
// will signal the end of the stream (EOF)
this.push(chunk);
},
write: function(chunk, encoding, next) {
// sets this._write under the hood
// An optional error can be passed as the first argument
next()
}
});
// or
var duplex = new stream.Duplex({
read: function(n) {
// sets this._read under the hood
// push data onto the read queue, passing null
// will signal the end of the stream (EOF)
this.push(chunk);
},
writev: function(chunks, next) {
// sets this._writev under the hood
// An optional error can be passed as the first argument
next()
}
});
</code></pre>
<h3>Readable<span><a class="mark" href="#stream_readable" id="stream_readable">#</a></span></h3>
<pre><code class="lang-js">var readable = new stream.Readable({
read: function(n) {
// sets this._read under the hood
// push data onto the read queue, passing null
// will signal the end of the stream (EOF)
this.push(chunk);
}
});
</code></pre>
<h3>Transform<span><a class="mark" href="#stream_transform" id="stream_transform">#</a></span></h3>
<pre><code class="lang-js">var transform = new stream.Transform({
transform: function(chunk, encoding, next) {
// sets this._transform under the hood
// generate output as many times as needed
// this.push(chunk);
// call when the current chunk is consumed
next();
},
flush: function(done) {
// sets this._flush under the hood
// generate output as many times as needed
// this.push(chunk);
done();
}
});
</code></pre>
<h3>Writable<span><a class="mark" href="#stream_writable" id="stream_writable">#</a></span></h3>
<pre><code class="lang-js">var writable = new stream.Writable({
write: function(chunk, encoding, next) {
// sets this._write under the hood
// An optional error can be passed as the first argument
next()
}
});
// or
var writable = new stream.Writable({
writev: function(chunks, next) {
// sets this._writev under the hood
// An optional error can be passed as the first argument
next()
}
});
</code></pre>
<h2>Streams: Under the Hood<span><a class="mark" href="#stream_streams_under_the_hood" id="stream_streams_under_the_hood">#</a></span></h2>
<!--type=misc-->
<h3>Buffering<span><a class="mark" href="#stream_buffering" id="stream_buffering">#</a></span></h3>
<!--type=misc-->
<p>Both Writable and Readable streams will buffer data on an internal
object which can be retrieved from <code>_writableState.getBuffer()</code> or
<code>_readableState.buffer</code>, respectively.</p>
<p>The amount of data that will potentially be buffered depends on the
<code>highWaterMark</code> option which is passed into the constructor.</p>
<p>Buffering in Readable streams happens when the implementation calls
<a href="#stream_readable_push_chunk_encoding"><code>stream.push(chunk)</code></a>. If the consumer of the Stream does not
call <a href="#stream_readable_read_size"><code>stream.read()</code></a>, then the data will sit in the internal
queue until it is consumed.</p>
<p>Buffering in Writable streams happens when the user calls
<a href="#stream_writable_write_chunk_encoding_callback"><code>stream.write(chunk)</code></a> repeatedly, even when it returns <code>false</code>.</p>
<p>The purpose of streams, especially with the <a href="#stream_readable_pipe_destination_options"><code>stream.pipe()</code></a> method, is to
limit the buffering of data to acceptable levels, so that sources and
destinations of varying speed will not overwhelm the available memory.</p>
<h3>Compatibility with Older Node.js Versions<span><a class="mark" href="#stream_compatibility_with_older_node_js_versions" id="stream_compatibility_with_older_node_js_versions">#</a></span></h3>
<!--type=misc-->
<p>In versions of Node.js prior to v0.10, the Readable stream interface was
simpler, but also less powerful and less useful.</p>
<ul>
<li>Rather than waiting for you to call the <a href="#stream_readable_read_size"><code>stream.read()</code></a> method,
<a href="#stream_event_data"><code>'data'</code></a> events would start emitting immediately. If you needed to do
some I/O to decide how to handle data, then you had to store the chunks
in some kind of buffer so that they would not be lost.</li>
<li>The <a href="#stream_readable_pause"><code>stream.pause()</code></a> method was advisory, rather than
guaranteed. This meant that you still had to be prepared to receive
<a href="#stream_event_data"><code>'data'</code></a> events even when the stream was in a paused state.</li>
</ul>
<p>In Node.js v0.10, the <a href="#stream_class_stream_readable">Readable</a> class was added.
For backwards compatibility with older Node.js programs, Readable streams
switch into "flowing mode" when a <a href="#stream_event_data"><code>'data'</code></a> event handler is added, or
when the <a href="#stream_readable_resume"><code>stream.resume()</code></a> method is called. The effect is
that, even if you are not using the new <a href="#stream_readable_read_size"><code>stream.read()</code></a> method
and <a href="#stream_event_readable"><code>'readable'</code></a> event, you no longer have to worry about losing
<a href="#stream_event_data"><code>'data'</code></a> chunks.</p>
<p>Most programs will continue to function normally. However, this
introduces an edge case in the following conditions:</p>
<ul>
<li>No <a href="#stream_event_data"><code>'data'</code></a> event handler is added.</li>
<li>The <a href="#stream_readable_resume"><code>stream.resume()</code></a> method is never called.</li>
<li>The stream is not piped to any writable destination.</li>
</ul>
<p>For example, consider the following code:</p>
<pre><code class="lang-js">// WARNING! BROKEN!
net.createServer((socket) => {
// we add an 'end' method, but never consume the data
socket.on('end', () => {
// It will never get here.
socket.end('I got your message (but didnt read it)\n');
});
}).listen(1337);
</code></pre>
<p>In versions of Node.js prior to v0.10, the incoming message data would be
simply discarded. However, in Node.js v0.10 and beyond,
the socket will remain paused forever.</p>
<p>The workaround in this situation is to call the
<a href="#stream_readable_resume"><code>stream.resume()</code></a> method to start the flow of data:</p>
<pre><code class="lang-js">// Workaround
net.createServer((socket) => {
socket.on('end', () => {
socket.end('I got your message (but didnt read it)\n');
});
// start the flow of data, discarding it.
socket.resume();
}).listen(1337);
</code></pre>
<p>In addition to new Readable streams switching into flowing mode,
pre-v0.10 style streams can be wrapped in a Readable class using the
<a href="#stream_readable_wrap_stream"><code>stream.wrap()</code></a> method.</p>
<h3>Object Mode<span><a class="mark" href="#stream_object_mode" id="stream_object_mode">#</a></span></h3>
<!--type=misc-->
<p>Normally, Streams operate on Strings and Buffers exclusively.</p>
<p>Streams that are in <strong>object mode</strong> can emit generic JavaScript values
other than Buffers and Strings.</p>
<p>A Readable stream in object mode will always return a single item from
a call to <a href="#stream_readable_read_size"><code>stream.read(size)</code></a>, regardless of what the size
argument is.</p>
<p>A Writable stream in object mode will always ignore the <code>encoding</code>
argument to <a href="#stream_writable_write_chunk_encoding_callback"><code>stream.write(data, encoding)</code></a>.</p>
<p>The special value <code>null</code> still retains its special value for object
mode streams. That is, for object mode readable streams, <code>null</code> as a
return value from <a href="#stream_readable_read_size"><code>stream.read()</code></a> indicates that there is no more
data, and <a href="#stream_readable_push_chunk_encoding"><code>stream.push(null)</code></a> will signal the end of stream data
(<code>EOF</code>).</p>
<p>No streams in Node.js core are object mode streams. This pattern is only
used by userland streaming libraries.</p>
<p>You should set <code>objectMode</code> in your stream child class constructor on
the options object. Setting <code>objectMode</code> mid-stream is not safe.</p>
<p>For Duplex streams <code>objectMode</code> can be set exclusively for readable or
writable side with <code>readableObjectMode</code> and <code>writableObjectMode</code>
respectively. These options can be used to implement parsers and
serializers with Transform streams.</p>
<pre><code class="lang-js">const util = require('util');
const StringDecoder = require('string_decoder').StringDecoder;
const Transform = require('stream').Transform;
util.inherits(JSONParseStream, Transform);
// Gets \n-delimited JSON string data, and emits the parsed objects
function JSONParseStream() {
if (!(this instanceof JSONParseStream))
return new JSONParseStream();
Transform.call(this, { readableObjectMode : true });
this._buffer = '';
this._decoder = new StringDecoder('utf8');
}
JSONParseStream.prototype._transform = function(chunk, encoding, cb) {
this._buffer += this._decoder.write(chunk);
// split on newlines
var lines = this._buffer.split(/\r?\n/);
// keep the last partial line buffered
this._buffer = lines.pop();
for (var l = 0; l < lines.length; l++) {
var line = lines[l];
try {
var obj = JSON.parse(line);
} catch (er) {
this.emit('error', er);
return;
}
// push the parsed object out to the readable consumer
this.push(obj);
}
cb();
};
JSONParseStream.prototype._flush = function(cb) {
// Just handle any leftover
var rem = this._buffer.trim();
if (rem) {
try {
var obj = JSON.parse(rem);
} catch (er) {
this.emit('error', er);
return;
}
// push the parsed object out to the readable consumer
this.push(obj);
}
cb();
};
</code></pre>
<h3><code>stream.read(0)</code><span><a class="mark" href="#stream_stream_read_0" id="stream_stream_read_0">#</a></span></h3>
<p>There are some cases where you want to trigger a refresh of the
underlying readable stream mechanisms, without actually consuming any
data. In that case, you can call <code>stream.read(0)</code>, which will always
return null.</p>
<p>If the internal read buffer is below the <code>highWaterMark</code>, and the
stream is not currently reading, then calling <code>stream.read(0)</code> will trigger
a low-level <a href="#stream_readable_read_size_1"><code>stream._read()</code></a> call.</p>
<p>There is almost never a need to do this. However, you will see some
cases in Node.js's internals where this is done, particularly in the
Readable stream class internals.</p>
<h3><code>stream.push('')</code><span><a class="mark" href="#stream_stream_push" id="stream_stream_push">#</a></span></h3>
<p>Pushing a zero-byte string or Buffer (when not in <a href="#stream_object_mode">Object mode</a>) has an
interesting side effect. Because it <em>is</em> a call to
<a href="#stream_readable_push_chunk_encoding"><code>stream.push()</code></a>, it will end the <code>reading</code> process. However, it
does <em>not</em> add any data to the readable buffer, so there's nothing for
a user to consume.</p>
<p>Very rarely, there are cases where you have no data to provide now,
but the consumer of your stream (or, perhaps, another bit of your own
code) will know when to check again, by calling <a href="#stream_readable_read_size"><code>stream.read(0)</code></a>.
In those cases, you <em>may</em> call <code>stream.push('')</code>.</p>
<p>So far, the only use case for this functionality is in the
<a href="tls.html#tls_class_cryptostream"><code>tls.CryptoStream</code></a> class, which is deprecated in Node.js/io.js v1.0. If you
find that you have to use <code>stream.push('')</code>, please consider another
approach, because it almost certainly indicates that something is
horribly wrong.</p>
<!-- [end-include:stream.md] -->
<!-- [start-include:string_decoder.md] -->
<h1>String Decoder<span><a class="mark" href="#string_decoder_string_decoder" id="string_decoder_string_decoder">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>To use this module, do <code>require('string_decoder')</code>. StringDecoder decodes a
buffer to a string. It is a simple interface to <code>buffer.toString()</code> but provides
additional support for utf8.</p>
<pre><code class="lang-js">const StringDecoder = require('string_decoder').StringDecoder;
const decoder = new StringDecoder('utf8');
const cent = new Buffer([0xC2, 0xA2]);
console.log(decoder.write(cent));
const euro = new Buffer([0xE2, 0x82, 0xAC]);
console.log(decoder.write(euro));
</code></pre>
<h2>Class: StringDecoder<span><a class="mark" href="#string_decoder_class_stringdecoder" id="string_decoder_class_stringdecoder">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><p>Accepts a single argument, <code>encoding</code> which defaults to <code>'utf8'</code>.</p>
<h3>decoder.end()<span><a class="mark" href="#string_decoder_decoder_end" id="string_decoder_decoder_end">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.3</span>
</div><p>Returns any trailing bytes that were left in the buffer.</p>
<h3>decoder.write(buffer)<span><a class="mark" href="#string_decoder_decoder_write_buffer" id="string_decoder_decoder_write_buffer">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.99</span>
</div><p>Returns a decoded string.</p>
<!-- [end-include:string_decoder.md] -->
<!-- [start-include:timers.md] -->
<h1>Timers<span><a class="mark" href="#timers_timers" id="timers_timers">#</a></span></h1>
<pre class="api_stability api_stability_3">Stability: 3 - Locked</pre><p>All of the timer functions are globals. You do not need to <code>require()</code>
this module in order to use them.</p>
<h2>clearImmediate(immediateObject)<span><a class="mark" href="#timers_clearimmediate_immediateobject" id="timers_clearimmediate_immediateobject">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>Stops an <code>immediateObject</code>, as created by <a href="timers.html#timers_setimmediate_callback_arg"><code>setImmediate</code></a>, from triggering.</p>
<h2>clearInterval(intervalObject)<span><a class="mark" href="#timers_clearinterval_intervalobject" id="timers_clearinterval_intervalobject">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><p>Stops an <code>intervalObject</code>, as created by <a href="timers.html#timers_setinterval_callback_delay_arg"><code>setInterval</code></a>, from triggering.</p>
<h2>clearTimeout(timeoutObject)<span><a class="mark" href="#timers_cleartimeout_timeoutobject" id="timers_cleartimeout_timeoutobject">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><p>Prevents a <code>timeoutObject</code>, as created by <a href="timers.html#timers_settimeout_callback_delay_arg"><code>setTimeout</code></a>, from triggering.</p>
<h2>ref()<span><a class="mark" href="#timers_ref" id="timers_ref">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>If a timer was previously <code>unref()</code>d, then <code>ref()</code> can be called to explicitly
request the timer hold the program open. If the timer is already <code>ref</code>d calling
<code>ref</code> again will have no effect.</p>
<p>Returns the timer.</p>
<h2>setImmediate(callback[, arg][, ...])<span><a class="mark" href="#timers_setimmediate_callback_arg" id="timers_setimmediate_callback_arg">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>Schedules "immediate" execution of <code>callback</code> after I/O events'
callbacks and before timers set by <a href="timers.html#timers_settimeout_callback_delay_arg"><code>setTimeout</code></a> and <a href="timers.html#timers_setinterval_callback_delay_arg"><code>setInterval</code></a> are
triggered. Returns an <code>immediateObject</code> for possible use with
<a href="timers.html#timers_clearimmediate_immediateobject"><code>clearImmediate</code></a>. Additional optional arguments may be passed to the
callback.</p>
<p>Callbacks for immediates are queued in the order in which they were created.
The entire callback queue is processed every event loop iteration. If an
immediate is queued from inside an executing callback, that immediate won't fire
until the next event loop iteration.</p>
<h2>setInterval(callback, delay[, arg][, ...])<span><a class="mark" href="#timers_setinterval_callback_delay_arg" id="timers_setinterval_callback_delay_arg">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><p>Schedules repeated execution of <code>callback</code> every <code>delay</code> milliseconds.
Returns a <code>intervalObject</code> for possible use with <a href="timers.html#timers_clearinterval_intervalobject"><code>clearInterval</code></a>. Additional
optional arguments may be passed to the callback.</p>
<p>To follow browser behavior, when using delays larger than 2147483647
milliseconds (approximately 25 days) or less than 1, Node.js will use 1 as the
<code>delay</code>.</p>
<h2>setTimeout(callback, delay[, arg][, ...])<span><a class="mark" href="#timers_settimeout_callback_delay_arg" id="timers_settimeout_callback_delay_arg">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.0.1</span>
</div><p>Schedules execution of a one-time <code>callback</code> after <code>delay</code> milliseconds.
Returns a <code>timeoutObject</code> for possible use with <a href="timers.html#timers_cleartimeout_timeoutobject"><code>clearTimeout</code></a>. Additional
optional arguments may be passed to the callback.</p>
<p>The callback will likely not be invoked in precisely <code>delay</code> milliseconds.
Node.js makes no guarantees about the exact timing of when callbacks will fire,
nor of their ordering. The callback will be called as close as possible to the
time specified.</p>
<p>To follow browser behavior, when using delays larger than 2147483647
milliseconds (approximately 25 days) or less than 1, the timeout is executed
immediately, as if the <code>delay</code> was set to 1.</p>
<h2>unref()<span><a class="mark" href="#timers_unref" id="timers_unref">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.9.1</span>
</div><p>The opaque value returned by <a href="timers.html#timers_settimeout_callback_delay_arg"><code>setTimeout</code></a> and <a href="timers.html#timers_setinterval_callback_delay_arg"><code>setInterval</code></a> also has the
method <code>timer.unref()</code> which allows the creation of a timer that is active but
if it is the only item left in the event loop, it won't keep the program
running. If the timer is already <code>unref</code>d calling <code>unref</code> again will have no
effect.</p>
<p>In the case of <a href="timers.html#timers_settimeout_callback_delay_arg"><code>setTimeout</code></a>, <code>unref</code> creates a separate timer that will
wakeup the event loop, creating too many of these may adversely effect event
loop performance -- use wisely.</p>
<p>Returns the timer.</p>
<!-- [end-include:timers.md] -->
<!-- [start-include:tls.md] -->
<h1>TLS (SSL)<span><a class="mark" href="#tls_tls_ssl" id="tls_tls_ssl">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>Use <code>require('tls')</code> to access this module.</p>
<p>The <code>tls</code> module uses OpenSSL to provide Transport Layer Security and/or
Secure Socket Layer: encrypted stream communication.</p>
<p>TLS/SSL is a public/private key infrastructure. Each client and each
server must have a private key. A private key is created like this:</p>
<pre><code>openssl genrsa -out ryans-key.pem 2048
</code></pre><p>All servers and some clients need to have a certificate. Certificates are public
keys signed by a Certificate Authority or self-signed. The first step to
getting a certificate is to create a "Certificate Signing Request" (CSR)
file. This is done with:</p>
<pre><code>openssl req -new -sha256 -key ryans-key.pem -out ryans-csr.pem
</code></pre><p>To create a self-signed certificate with the CSR, do this:</p>
<pre><code>openssl x509 -req -in ryans-csr.pem -signkey ryans-key.pem -out ryans-cert.pem
</code></pre><p>Alternatively you can send the CSR to a Certificate Authority for signing.</p>
<p>For Perfect Forward Secrecy, it is required to generate Diffie-Hellman
parameters:</p>
<pre><code>openssl dhparam -outform PEM -out dhparam.pem 2048
</code></pre><p>To create .pfx or .p12, do this:</p>
<pre><code>openssl pkcs12 -export -in agent5-cert.pem -inkey agent5-key.pem \
-certfile ca-cert.pem -out agent5.pfx
</code></pre><ul>
<li><code>in</code>: certificate</li>
<li><code>inkey</code>: private key</li>
<li><code>certfile</code>: all CA certs concatenated in one file like
<code>cat ca1-cert.pem ca2-cert.pem > ca-cert.pem</code></li>
</ul>
<h2>Client-initiated renegotiation attack mitigation<span><a class="mark" href="#tls_client_initiated_renegotiation_attack_mitigation" id="tls_client_initiated_renegotiation_attack_mitigation">#</a></span></h2>
<!-- type=misc -->
<p>The TLS protocol lets the client renegotiate certain aspects of the TLS session.
Unfortunately, session renegotiation requires a disproportional amount of
server-side resources, which makes it a potential vector for denial-of-service
attacks.</p>
<p>To mitigate this, renegotiations are limited to three times every 10 minutes. An
error is emitted on the <a href="#tls_class_tls_tlssocket"><code>tls.TLSSocket</code></a> instance when the threshold is
exceeded. The limits are configurable:</p>
<ul>
<li><p><code>tls.CLIENT_RENEG_LIMIT</code>: renegotiation limit, default is 3.</p>
</li>
<li><p><code>tls.CLIENT_RENEG_WINDOW</code>: renegotiation window in seconds, default is
10 minutes.</p>
</li>
</ul>
<p>Don't change the defaults unless you know what you are doing.</p>
<p>To test your server, connect to it with <code>openssl s_client -connect address:port</code>
and tap <code>R<CR></code> (that's the letter <code>R</code> followed by a carriage return) a few
times.</p>
<h2>Modifying the Default TLS Cipher suite<span><a class="mark" href="#tls_modifying_the_default_tls_cipher_suite" id="tls_modifying_the_default_tls_cipher_suite">#</a></span></h2>
<p>Node.js is built with a default suite of enabled and disabled TLS ciphers.
Currently, the default cipher suite is:</p>
<pre><code>ECDHE-RSA-AES128-GCM-SHA256:
ECDHE-ECDSA-AES128-GCM-SHA256:
ECDHE-RSA-AES256-GCM-SHA384:
ECDHE-ECDSA-AES256-GCM-SHA384:
DHE-RSA-AES128-GCM-SHA256:
ECDHE-RSA-AES128-SHA256:
DHE-RSA-AES128-SHA256:
ECDHE-RSA-AES256-SHA384:
DHE-RSA-AES256-SHA384:
ECDHE-RSA-AES256-SHA256:
DHE-RSA-AES256-SHA256:
HIGH:
!aNULL:
!eNULL:
!EXPORT:
!DES:
!RC4:
!MD5:
!PSK:
!SRP:
!CAMELLIA
</code></pre><p>This default can be overriden entirely using the <code>--tls-cipher-list</code> command
line switch. For instance, the following makes
<code>ECDHE-RSA-AES128-GCM-SHA256:!RC4</code> the default TLS cipher suite:</p>
<pre><code>node --tls-cipher-list="ECDHE-RSA-AES128-GCM-SHA256:!RC4"
</code></pre><p>Note that the default cipher suite included within Node.js has been carefully
selected to reflect current security best practices and risk mitigation.
Changing the default cipher suite can have a significant impact on the security
of an application. The <code>--tls-cipher-list</code> switch should by used only if
absolutely necessary.</p>
<h2>ALPN, NPN and SNI<span><a class="mark" href="#tls_alpn_npn_and_sni" id="tls_alpn_npn_and_sni">#</a></span></h2>
<!-- type=misc -->
<p>ALPN (Application-Layer Protocol Negotiation Extension), NPN (Next
Protocol Negotiation) and SNI (Server Name Indication) are TLS
handshake extensions allowing you:</p>
<ul>
<li>ALPN/NPN - to use one TLS server for multiple protocols (HTTP, SPDY, HTTP/2)</li>
<li>SNI - to use one TLS server for multiple hostnames with different SSL
certificates.</li>
</ul>
<h2>Perfect Forward Secrecy<span><a class="mark" href="#tls_perfect_forward_secrecy" id="tls_perfect_forward_secrecy">#</a></span></h2>
<!-- type=misc -->
<p>The term "<a href="https://en.wikipedia.org/wiki/Perfect_forward_secrecy">Forward Secrecy</a>" or "Perfect Forward Secrecy" describes a feature of
key-agreement (i.e. key-exchange) methods. Practically it means that even if the
private key of a (your) server is compromised, communication can only be
decrypted by eavesdroppers if they manage to obtain the key-pair specifically
generated for each session.</p>
<p>This is achieved by randomly generating a key pair for key-agreement on every
handshake (in contrary to the same key for all sessions). Methods implementing
this technique, thus offering Perfect Forward Secrecy, are called "ephemeral".</p>
<p>Currently two methods are commonly used to achieve Perfect Forward Secrecy (note
the character "E" appended to the traditional abbreviations):</p>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange">DHE</a> - An ephemeral version of the Diffie Hellman key-agreement protocol.</li>
<li><a href="https://en.wikipedia.org/wiki/Elliptic_curve_Diffie%E2%80%93Hellman">ECDHE</a> - An ephemeral version of the Elliptic Curve Diffie Hellman
key-agreement protocol.</li>
</ul>
<p>Ephemeral methods may have some performance drawbacks, because key generation
is expensive.</p>
<h2>Class: CryptoStream<span><a class="mark" href="#tls_class_cryptostream" id="tls_class_cryptostream">#</a></span></h2>
<pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="#tls_class_tls_tlssocket"><code>tls.TLSSocket</code></a> instead.</pre><p>This is an encrypted stream.</p>
<h3>cryptoStream.bytesWritten<span><a class="mark" href="#tls_cryptostream_byteswritten" id="tls_cryptostream_byteswritten">#</a></span></h3>
<p>A proxy to the underlying socket's bytesWritten accessor, this will return
the total bytes written to the socket, <em>including the TLS overhead</em>.</p>
<h2>Class: SecurePair<span><a class="mark" href="#tls_class_securepair" id="tls_class_securepair">#</a></span></h2>
<p>Returned by tls.createSecurePair.</p>
<h3>Event: 'secure'<span><a class="mark" href="#tls_event_secure" id="tls_event_secure">#</a></span></h3>
<p>The event is emitted from the SecurePair once the pair has successfully
established a secure connection.</p>
<p>Similarly to the checking for the server <code>'secureConnection'</code> event,
pair.cleartext.authorized should be checked to confirm whether the certificate
used properly authorized.</p>
<h2>Class: tls.Server<span><a class="mark" href="#tls_class_tls_server" id="tls_class_tls_server">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.2</span>
</div><p>This class is a subclass of <code>net.Server</code> and has the same methods on it.
Instead of accepting just raw TCP connections, this accepts encrypted
connections using TLS or SSL.</p>
<h3>Event: 'clientError'<span><a class="mark" href="#tls_event_clienterror" id="tls_event_clienterror">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.11</span>
</div><p><code>function (exception, tlsSocket) { }</code></p>
<p>When a client connection emits an <code>'error'</code> event before a secure connection is
established it will be forwarded here.</p>
<p><code>tlsSocket</code> is the <a href="#tls_class_tls_tlssocket"><code>tls.TLSSocket</code></a> that the error originated from.</p>
<h3>Event: 'newSession'<span><a class="mark" href="#tls_event_newsession" id="tls_event_newsession">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.2</span>
</div><p><code>function (sessionId, sessionData, callback) { }</code></p>
<p>Emitted on creation of TLS session. May be used to store sessions in external
storage. <code>callback</code> must be invoked eventually, otherwise no data will be
sent or received from secure connection.</p>
<p>NOTE: adding this event listener will have an effect only on connections
established after addition of event listener.</p>
<h3>Event: 'OCSPRequest'<span><a class="mark" href="#tls_event_ocsprequest" id="tls_event_ocsprequest">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.13</span>
</div><p><code>function (certificate, issuer, callback) { }</code></p>
<p>Emitted when the client sends a certificate status request. You could parse
server's current certificate to obtain OCSP url and certificate id, and after
obtaining OCSP response invoke <code>callback(null, resp)</code>, where <code>resp</code> is a
<code>Buffer</code> instance. Both <code>certificate</code> and <code>issuer</code> are a <code>Buffer</code>
DER-representations of the primary and issuer's certificates. They could be used
to obtain OCSP certificate id and OCSP endpoint url.</p>
<p>Alternatively, <code>callback(null, null)</code> could be called, meaning that there is no
OCSP response.</p>
<p>Calling <code>callback(err)</code> will result in a <code>socket.destroy(err)</code> call.</p>
<p>Typical flow:</p>
<ol>
<li>Client connects to server and sends <code>'OCSPRequest'</code> to it (via status info
extension in ClientHello.)</li>
<li>Server receives request and invokes <code>'OCSPRequest'</code> event listener if present</li>
<li>Server grabs OCSP url from either <code>certificate</code> or <code>issuer</code> and performs an
<a href="https://en.wikipedia.org/wiki/OCSP_stapling">OCSP request</a> to the CA</li>
<li>Server receives <code>OCSPResponse</code> from CA and sends it back to client via
<code>callback</code> argument</li>
<li>Client validates the response and either destroys socket or performs a
handshake.</li>
</ol>
<p>NOTE: <code>issuer</code> could be null, if the certificate is self-signed or if the issuer
is not in the root certificates list. (You could provide an issuer via <code>ca</code>
option.)</p>
<p>NOTE: adding this event listener will have an effect only on connections
established after addition of event listener.</p>
<p>NOTE: you may want to use some npm module like <a href="https://npmjs.org/package/asn1.js">asn1.js</a> to parse the
certificates.</p>
<h3>Event: 'resumeSession'<span><a class="mark" href="#tls_event_resumesession" id="tls_event_resumesession">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.9.2</span>
</div><p><code>function (sessionId, callback) { }</code></p>
<p>Emitted when client wants to resume previous TLS session. Event listener may
perform lookup in external storage using given <code>sessionId</code>, and invoke
<code>callback(null, sessionData)</code> once finished. If session can't be resumed
(i.e. doesn't exist in storage) one may call <code>callback(null, null)</code>. Calling
<code>callback(err)</code> will terminate incoming connection and destroy socket.</p>
<p>NOTE: adding this event listener will have an effect only on connections
established after addition of event listener.</p>
<p>Here's an example for using TLS session resumption:</p>
<pre><code class="lang-js">var tlsSessionStore = {};
server.on('newSession', (id, data, cb) => {
tlsSessionStore[id.toString('hex')] = data;
cb();
});
server.on('resumeSession', (id, cb) => {
cb(null, tlsSessionStore[id.toString('hex')] || null);
});
</code></pre>
<h3>Event: 'secureConnection'<span><a class="mark" href="#tls_event_secureconnection" id="tls_event_secureconnection">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.2</span>
</div><p><code>function (tlsSocket) {}</code></p>
<p>This event is emitted after a new connection has been successfully
handshaked. The argument is an instance of <a href="#tls_class_tls_tlssocket"><code>tls.TLSSocket</code></a>. It has all the
common stream methods and events.</p>
<p><code>socket.authorized</code> is a boolean value which indicates if the
client has verified by one of the supplied certificate authorities for the
server. If <code>socket.authorized</code> is false, then
<code>socket.authorizationError</code> is set to describe how authorization
failed. Implied but worth mentioning: depending on the settings of the TLS
server, you unauthorized connections may be accepted.</p>
<p><code>socket.npnProtocol</code> is a string containing the selected NPN protocol
and <code>socket.alpnProtocol</code> is a string containing the selected ALPN
protocol, When both NPN and ALPN extensions are received, ALPN takes
precedence over NPN and the next protocol is selected by ALPN. When
ALPN has no selected protocol, this returns false.</p>
<p><code>socket.servername</code> is a string containing servername requested with
SNI.</p>
<h3>server.addContext(hostname, context)<span><a class="mark" href="#tls_server_addcontext_hostname_context" id="tls_server_addcontext_hostname_context">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.3</span>
</div><p>Add secure context that will be used if client request's SNI hostname is
matching passed <code>hostname</code> (wildcards can be used). <code>context</code> can contain
<code>key</code>, <code>cert</code>, <code>ca</code> and/or any other properties from
<a href="#tls_tls_createsecurecontext_details"><code>tls.createSecureContext()</code></a> <code>options</code> argument.</p>
<h3>server.address()<span><a class="mark" href="#tls_server_address" id="tls_server_address">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><p>Returns the bound address, the address family name and port of the
server as reported by the operating system. See <a href="net.html#net_server_address"><code>net.Server.address()</code></a> for
more information.</p>
<h3>server.close([callback])<span><a class="mark" href="#tls_server_close_callback" id="tls_server_close_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.2</span>
</div><p>Stops the server from accepting new connections. This function is
asynchronous, the server is finally closed when the server emits a <code>'close'</code>
event. Optionally, you can pass a callback to listen for the <code>'close'</code> event.</p>
<h3>server.connections<span><a class="mark" href="#tls_server_connections" id="tls_server_connections">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.2</span>
</div><p>The number of concurrent connections on the server.</p>
<h3>server.getTicketKeys()<span><a class="mark" href="#tls_server_getticketkeys" id="tls_server_getticketkeys">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v3.0.0</span>
</div><p>Returns <code>Buffer</code> instance holding the keys currently used for
encryption/decryption of the <a href="https://www.ietf.org/rfc/rfc5077.txt">TLS Session Tickets</a></p>
<h3>server.listen(port[, hostname][, callback])<span><a class="mark" href="#tls_server_listen_port_hostname_callback" id="tls_server_listen_port_hostname_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.2</span>
</div><p>Begin accepting connections on the specified <code>port</code> and <code>hostname</code>. If the
<code>hostname</code> is omitted, the server will accept connections on any IPv6 address
(<code>::</code>) when IPv6 is available, or any IPv4 address (<code>0.0.0.0</code>) otherwise. A
port value of zero will assign a random port.</p>
<p>This function is asynchronous. The last parameter <code>callback</code> will be called
when the server has been bound.</p>
<p>See <a href="net.html#net_class_net_server"><code>net.Server</code></a> for more information.</p>
<h3>server.maxConnections<span><a class="mark" href="#tls_server_maxconnections" id="tls_server_maxconnections">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.2.0</span>
</div><p>Set this property to reject connections when the server's connection count
gets high.</p>
<h3>server.setTicketKeys(keys)<span><a class="mark" href="#tls_server_setticketkeys_keys" id="tls_server_setticketkeys_keys">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v3.0.0</span>
</div><p>Updates the keys for encryption/decryption of the <a href="https://www.ietf.org/rfc/rfc5077.txt">TLS Session Tickets</a>.</p>
<p>NOTE: the buffer should be 48 bytes long. See server <code>ticketKeys</code> option for
more information oh how it is going to be used.</p>
<p>NOTE: the change is effective only for the future server connections. Existing
or currently pending server connections will use previous keys.</p>
<h2>Class: tls.TLSSocket<span><a class="mark" href="#tls_class_tls_tlssocket" id="tls_class_tls_tlssocket">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>This is a wrapped version of <a href="net.html#net_class_net_socket"><code>net.Socket</code></a> that does transparent encryption
of written data and all required TLS negotiation.</p>
<p>This instance implements a duplex <a href="stream.html#stream_stream">Stream</a> interfaces. It has all the
common stream methods and events.</p>
<p>Methods that return TLS connection meta data (e.g.
<a href="#tls_tlssocket_getpeercertificate_detailed"><code>tls.TLSSocket.getPeerCertificate()</code></a> will only return data while the
connection is open.</p>
<h2>new tls.TLSSocket(socket[, options])<span><a class="mark" href="#tls_new_tls_tlssocket_socket_options" id="tls_new_tls_tlssocket_socket_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Construct a new TLSSocket object from existing TCP socket.</p>
<p><code>socket</code> is an instance of <a href="net.html#net_class_net_socket"><code>net.Socket</code></a></p>
<p><code>options</code> is an optional object that might contain following properties:</p>
<ul>
<li><p><code>secureContext</code>: An optional TLS context object from
<a href="#tls_tls_createsecurecontext_details"><code>tls.createSecureContext()</code></a></p>
</li>
<li><p><code>isServer</code>: If <code>true</code> the TLS socket will be instantiated in server-mode.
Default: <code>false</code></p>
</li>
<li><p><code>server</code>: An optional <a href="net.html#net_class_net_server"><code>net.Server</code></a> instance</p>
</li>
<li><p><code>requestCert</code>: Optional, see <a href="#tls_tls_createsecurepair_context_isserver_requestcert_rejectunauthorized_options"><code>tls.createSecurePair()</code></a></p>
</li>
<li><p><code>rejectUnauthorized</code>: Optional, see <a href="#tls_tls_createsecurepair_context_isserver_requestcert_rejectunauthorized_options"><code>tls.createSecurePair()</code></a></p>
</li>
<li><p><code>NPNProtocols</code>: Optional, see <a href="#tls_tls_createserver_options_secureconnectionlistener"><code>tls.createServer()</code></a></p>
</li>
<li><p><code>ALPNProtocols</code>: Optional, see [tls.createServer][]</p>
</li>
<li><p><code>SNICallback</code>: Optional, see <a href="#tls_tls_createserver_options_secureconnectionlistener"><code>tls.createServer()</code></a></p>
</li>
<li><p><code>session</code>: Optional, a <code>Buffer</code> instance, containing TLS session</p>
</li>
<li><p><code>requestOCSP</code>: Optional, if <code>true</code> the OCSP status request extension will
be added to the client hello, and an <code>'OCSPResponse'</code> event will be emitted
on the socket before establishing a secure communication</p>
</li>
</ul>
<h3>Event: 'OCSPResponse'<span><a class="mark" href="#tls_event_ocspresponse" id="tls_event_ocspresponse">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.13</span>
</div><p><code>function (response) { }</code></p>
<p>This event will be emitted if <code>requestOCSP</code> option was set. <code>response</code> is a
buffer object, containing server's OCSP response.</p>
<p>Traditionally, the <code>response</code> is a signed object from the server's CA that
contains information about server's certificate revocation status.</p>
<h3>Event: 'secureConnect'<span><a class="mark" href="#tls_event_secureconnect" id="tls_event_secureconnect">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>This event is emitted after a new connection has been successfully handshaked.
The listener will be called no matter if the server's certificate was
authorized or not. It is up to the user to test <code>tlsSocket.authorized</code>
to see if the server certificate was signed by one of the specified CAs.
If <code>tlsSocket.authorized === false</code> then the error can be found in
<code>tlsSocket.authorizationError</code>. Also if ALPN or NPN was used - you can
check <code>tlsSocket.alpnProtocol</code> or <code>tlsSocket.npnProtocol</code> for the
negotiated protocol.</p>
<h3>tlsSocket.address()<span><a class="mark" href="#tls_tlssocket_address" id="tls_tlssocket_address">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Returns the bound address, the address family name and port of the
underlying socket as reported by the operating system. Returns an
object with three properties, e.g.
<code>{ port: 12346, family: 'IPv4', address: '127.0.0.1' }</code></p>
<h3>tlsSocket.authorized<span><a class="mark" href="#tls_tlssocket_authorized" id="tls_tlssocket_authorized">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>A boolean that is <code>true</code> if the peer certificate was signed by one of the
specified CAs, otherwise <code>false</code></p>
<h3>tlsSocket.authorizationError<span><a class="mark" href="#tls_tlssocket_authorizationerror" id="tls_tlssocket_authorizationerror">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>The reason why the peer's certificate has not been verified. This property
becomes available only when <code>tlsSocket.authorized === false</code>.</p>
<h3>tlsSocket.encrypted<span><a class="mark" href="#tls_tlssocket_encrypted" id="tls_tlssocket_encrypted">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Static boolean value, always <code>true</code>. May be used to distinguish TLS sockets
from regular ones.</p>
<h3>tlsSocket.getCipher()<span><a class="mark" href="#tls_tlssocket_getcipher" id="tls_tlssocket_getcipher">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Returns an object representing the cipher name and the SSL/TLS
protocol version of the current connection.</p>
<p>Example:
<span class="type"><name: 'AES256-SHA', version: 'TLSv1/SSLv3'></span></p>
<p>See SSL_CIPHER_get_name() and SSL_CIPHER_get_version() in
<a href="https://www.openssl.org/docs/ssl/ssl.html#DEALING-WITH-CIPHERS">https://www.openssl.org/docs/ssl/ssl.html#DEALING-WITH-CIPHERS</a> for more
information.</p>
<h3>tlsSocket.getPeerCertificate([ detailed ])<span><a class="mark" href="#tls_tlssocket_getpeercertificate_detailed" id="tls_tlssocket_getpeercertificate_detailed">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Returns an object representing the peer's certificate. The returned object has
some properties corresponding to the field of the certificate. If <code>detailed</code>
argument is <code>true</code> the full chain with <code>issuer</code> property will be returned,
if <code>false</code> only the top certificate without <code>issuer</code> property.</p>
<p>Example:</p>
<pre><code>{ subject:
{ C: 'UK',
ST: 'Acknack Ltd',
L: 'Rhys Jones',
O: 'node.js',
OU: 'Test TLS Certificate',
CN: 'localhost' },
issuerInfo:
{ C: 'UK',
ST: 'Acknack Ltd',
L: 'Rhys Jones',
O: 'node.js',
OU: 'Test TLS Certificate',
CN: 'localhost' },
issuer:
{ ... another certificate ... },
raw: < RAW DER buffer >,
valid_from: 'Nov 11 09:52:22 2009 GMT',
valid_to: 'Nov 6 09:52:22 2029 GMT',
fingerprint: '2A:7A:C2:DD:E5:F9:CC:53:72:35:99:7A:02:5A:71:38:52:EC:8A:DF',
serialNumber: 'B9B0D332A1AA5635' }
</code></pre><p>If the peer does not provide a certificate, it returns <code>null</code> or an empty
object.</p>
<h3>tlsSocket.getSession()<span><a class="mark" href="#tls_tlssocket_getsession" id="tls_tlssocket_getsession">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Return ASN.1 encoded TLS session or <code>undefined</code> if none was negotiated. Could
be used to speed up handshake establishment when reconnecting to the server.</p>
<h3>tlsSocket.getTLSTicket()<span><a class="mark" href="#tls_tlssocket_gettlsticket" id="tls_tlssocket_gettlsticket">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>NOTE: Works only with client TLS sockets. Useful only for debugging, for
session reuse provide <code>session</code> option to <a href="#tls_tls_connect_options_callback"><code>tls.connect()</code></a>.</p>
<p>Return TLS session ticket or <code>undefined</code> if none was negotiated.</p>
<h3>tlsSocket.localPort<span><a class="mark" href="#tls_tlssocket_localport" id="tls_tlssocket_localport">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>The numeric representation of the local port.</p>
<h3>tlsSocket.localAddress<span><a class="mark" href="#tls_tlssocket_localaddress" id="tls_tlssocket_localaddress">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>The string representation of the local IP address.</p>
<h3>tlsSocket.remoteAddress<span><a class="mark" href="#tls_tlssocket_remoteaddress" id="tls_tlssocket_remoteaddress">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>The string representation of the remote IP address. For example,
<code>'74.125.127.100'</code> or <code>'2001:4860:a005::68'</code>.</p>
<h3>tlsSocket.remoteFamily<span><a class="mark" href="#tls_tlssocket_remotefamily" id="tls_tlssocket_remotefamily">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>The string representation of the remote IP family. <code>'IPv4'</code> or <code>'IPv6'</code>.</p>
<h3>tlsSocket.remotePort<span><a class="mark" href="#tls_tlssocket_remoteport" id="tls_tlssocket_remoteport">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>The numeric representation of the remote port. For example, <code>443</code>.</p>
<h3>tlsSocket.renegotiate(options, callback)<span><a class="mark" href="#tls_tlssocket_renegotiate_options_callback" id="tls_tlssocket_renegotiate_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.8</span>
</div><p>Initiate TLS renegotiation process. The <code>options</code> may contain the following
fields: <code>rejectUnauthorized</code>, <code>requestCert</code> (See <a href="#tls_tls_createserver_options_secureconnectionlistener"><code>tls.createServer()</code></a> for
details). <code>callback(err)</code> will be executed with <code>null</code> as <code>err</code>,
once the renegotiation is successfully completed.</p>
<p>NOTE: Can be used to request peer's certificate after the secure connection
has been established.</p>
<p>ANOTHER NOTE: When running as the server, socket will be destroyed
with an error after <code>handshakeTimeout</code> timeout.</p>
<h3>tlsSocket.setMaxSendFragment(size)<span><a class="mark" href="#tls_tlssocket_setmaxsendfragment_size" id="tls_tlssocket_setmaxsendfragment_size">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.11</span>
</div><p>Set maximum TLS fragment size (default and maximum value is: <code>16384</code>, minimum
is: <code>512</code>). Returns <code>true</code> on success, <code>false</code> otherwise.</p>
<p>Smaller fragment size decreases buffering latency on the client: large
fragments are buffered by the TLS layer until the entire fragment is received
and its integrity is verified; large fragments can span multiple roundtrips,
and their processing can be delayed due to packet loss or reordering. However,
smaller fragments add extra TLS framing bytes and CPU overhead, which may
decrease overall server throughput.</p>
<h2>tls.connect(options[, callback])<span><a class="mark" href="#tls_tls_connect_options_callback" id="tls_tls_connect_options_callback">#</a></span></h2>
<h2>tls.connect(port[, host][, options][, callback])<span><a class="mark" href="#tls_tls_connect_port_host_options_callback" id="tls_tls_connect_port_host_options_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.3</span>
</div><p>Creates a new client connection to the given <code>port</code> and <code>host</code> (old API) or
<code>options.port</code> and <code>options.host</code>. (If <code>host</code> is omitted, it defaults to
<code>localhost</code>.) <code>options</code> should be an object which specifies:</p>
<ul>
<li><p><code>host</code>: Host the client should connect to</p>
</li>
<li><p><code>port</code>: Port the client should connect to</p>
</li>
<li><p><code>socket</code>: Establish secure connection on a given socket rather than
creating a new socket. If this option is specified, <code>host</code> and <code>port</code>
are ignored.</p>
</li>
<li><p><code>path</code>: Creates unix socket connection to path. If this option is
specified, <code>host</code> and <code>port</code> are ignored.</p>
</li>
<li><p><code>pfx</code>: A string or <code>Buffer</code> containing the private key, certificate and
CA certs of the client in PFX or PKCS12 format.</p>
</li>
<li><p><code>key</code>: A string or <code>Buffer</code> containing the private key of the client in
PEM format. (Could be an array of keys).</p>
</li>
<li><p><code>passphrase</code>: A string of passphrase for the private key or pfx.</p>
</li>
<li><p><code>cert</code>: A string or <code>Buffer</code> containing the certificate key of the client in
PEM format. (Could be an array of certs).</p>
</li>
<li><p><code>ca</code>: A string, <code>Buffer</code> or array of strings or <code>Buffer</code>s of trusted
certificates in PEM format. If this is omitted several well known "root"
CAs will be used, like VeriSign. These are used to authorize connections.</p>
</li>
<li><p><code>ciphers</code>: A string describing the ciphers to use or exclude, separated by
<code>:</code>. Uses the same default cipher suite as <a href="#tls_tls_createserver_options_secureconnectionlistener"><code>tls.createServer()</code></a>.</p>
</li>
<li><p><code>rejectUnauthorized</code>: If <code>true</code>, the server certificate is verified against
the list of supplied CAs. An <code>'error'</code> event is emitted if verification
fails; <code>err.code</code> contains the OpenSSL error code. Default: <code>true</code>.</p>
</li>
<li><p><code>NPNProtocols</code>: An array of strings or <code>Buffer</code>s containing supported NPN
protocols. <code>Buffer</code>s should have following format: <code>0x05hello0x05world</code>,
where first byte is next protocol name's length. (Passing array should
usually be much simpler: <code>['hello', 'world']</code>.)</p>
</li>
<li><p><code>ALPNProtocols</code>: An array of strings or <code>Buffer</code>s containing
supported ALPN protocols. <code>Buffer</code>s should have following format:
<code>0x05hello0x05world</code>, where the first byte is the next protocol
name's length. (Passing array should usually be much simpler:
<code>['hello', 'world']</code>.)</p>
</li>
<li><p><code>servername</code>: Servername for SNI (Server Name Indication) TLS extension.</p>
</li>
<li><p><code>checkServerIdentity(servername, cert)</code>: Provide an override for checking
server's hostname against the certificate. Should return an error if verification
fails. Return <code>undefined</code> if passing.</p>
</li>
<li><p><code>secureProtocol</code>: The SSL method to use, e.g. <code>SSLv3_method</code> to force
SSL version 3. The possible values depend on your installation of
OpenSSL and are defined in the constant <a href="https://www.openssl.org/docs/ssl/ssl.html#DEALING-WITH-PROTOCOL-METHODS">SSL_METHODS</a>.</p>
</li>
<li><p><code>secureContext</code>: An optional TLS context object from
<code>tls.createSecureContext( ... )</code>. Could it be used for caching client
certificates, key, and CA certificates.</p>
</li>
<li><p><code>session</code>: A <code>Buffer</code> instance, containing TLS session.</p>
</li>
</ul>
<p>The <code>callback</code> parameter will be added as a listener for the
<a href="#tls_event_secureconnect"><code>'secureConnect'</code></a> event.</p>
<p><code>tls.connect()</code> returns a <a href="#tls_class_tls_tlssocket"><code>tls.TLSSocket</code></a> object.</p>
<p>Here is an example of a client of echo server as described previously:</p>
<pre><code class="lang-js">const tls = require('tls');
const fs = require('fs');
const options = {
// These are necessary only if using the client certificate authentication
key: fs.readFileSync('client-key.pem'),
cert: fs.readFileSync('client-cert.pem'),
// This is necessary only if the server uses the self-signed certificate
ca: [ fs.readFileSync('server-cert.pem') ]
};
var socket = tls.connect(8000, options, () => {
console.log('client connected',
socket.authorized ? 'authorized' : 'unauthorized');
process.stdin.pipe(socket);
process.stdin.resume();
});
socket.setEncoding('utf8');
socket.on('data', (data) => {
console.log(data);
});
socket.on('end', () => {
server.close();
});
</code></pre>
<p>Or</p>
<pre><code class="lang-js">const tls = require('tls');
const fs = require('fs');
const options = {
pfx: fs.readFileSync('client.pfx')
};
var socket = tls.connect(8000, options, () => {
console.log('client connected',
socket.authorized ? 'authorized' : 'unauthorized');
process.stdin.pipe(socket);
process.stdin.resume();
});
socket.setEncoding('utf8');
socket.on('data', (data) => {
console.log(data);
});
socket.on('end', () => {
server.close();
});
</code></pre>
<h2>tls.createSecureContext(details)<span><a class="mark" href="#tls_tls_createsecurecontext_details" id="tls_tls_createsecurecontext_details">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.13</span>
</div><p>Creates a credentials object, with the optional details being a
dictionary with keys:</p>
<ul>
<li><code>pfx</code> : A string or buffer holding the PFX or PKCS12 encoded private
key, certificate and CA certificates</li>
<li><code>key</code>: A string or <code>Buffer</code> containing the private key of the server in
PEM format. To support multiple keys using different algorithms, an array
can be provided. It can either be a plain array of keys, or an array of
objects in the format <code>{pem: key, passphrase: passphrase}</code>. (Required)</li>
<li><code>passphrase</code> : A string of passphrase for the private key or pfx</li>
<li><code>cert</code> : A string holding the PEM encoded certificate</li>
<li><code>ca</code>: A string, <code>Buffer</code> or array of strings or <code>Buffer</code>s of trusted
certificates in PEM format. If this is omitted several well known "root"
CAs will be used, like VeriSign. These are used to authorize connections.</li>
<li><code>crl</code> : Either a string or list of strings of PEM encoded CRLs
(Certificate Revocation List)</li>
<li><code>ciphers</code>: A string describing the ciphers to use or exclude.
Consult
<a href="https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT">https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT</a>
for details on the format.</li>
<li><code>honorCipherOrder</code> : When choosing a cipher, use the server's preferences
instead of the client preferences. For further details see <code>tls</code> module
documentation.</li>
</ul>
<p>If no 'ca' details are given, then Node.js will use the default
publicly trusted list of CAs as given in
<a href="http://mxr.mozilla.org/mozilla/source/security/nss/lib/ckfw/builtins/certdata.txt">http://mxr.mozilla.org/mozilla/source/security/nss/lib/ckfw/builtins/certdata.txt</a>.</p>
<h2>tls.createSecurePair([context][, isServer][, requestCert][, rejectUnauthorized][, options])<span><a class="mark" href="#tls_tls_createsecurepair_context_isserver_requestcert_rejectunauthorized_options" id="tls_tls_createsecurepair_context_isserver_requestcert_rejectunauthorized_options">#</a></span></h2>
<p>Creates a new secure pair object with two streams, one of which reads/writes
encrypted data, and one reads/writes cleartext data.
Generally the encrypted one is piped to/from an incoming encrypted data stream,
and the cleartext one is used as a replacement for the initial encrypted stream.</p>
<ul>
<li><p><code>credentials</code>: A secure context object from tls.createSecureContext( ... )</p>
</li>
<li><p><code>isServer</code>: A boolean indicating whether this tls connection should be
opened as a server or a client.</p>
</li>
<li><p><code>requestCert</code>: A boolean indicating whether a server should request a
certificate from a connecting client. Only applies to server connections.</p>
</li>
<li><p><code>rejectUnauthorized</code>: A boolean indicating whether a server should
automatically reject clients with invalid certificates. Only applies to
servers with <code>requestCert</code> enabled.</p>
</li>
<li><p><code>options</code>: An object with common SSL options. See <a href="#tls_class_tls_tlssocket"><code>tls.TLSSocket</code></a>.</p>
</li>
</ul>
<p><code>tls.createSecurePair()</code> returns a SecurePair object with <code>cleartext</code> and
<code>encrypted</code> stream properties.</p>
<p>NOTE: <code>cleartext</code> has the same APIs as <a href="#tls_class_tls_tlssocket"><code>tls.TLSSocket</code></a></p>
<h2>tls.createServer(options[, secureConnectionListener])<span><a class="mark" href="#tls_tls_createserver_options_secureconnectionlistener" id="tls_tls_createserver_options_secureconnectionlistener">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.2</span>
</div><p>Creates a new <a href="#tls_class_tls_server">tls.Server</a>. The <code>connectionListener</code> argument is
automatically set as a listener for the <a href="#tls_event_secureconnection"><code>'secureConnection'</code></a> event. The
<code>options</code> object has these possibilities:</p>
<ul>
<li><p><code>pfx</code>: A string or <code>Buffer</code> containing the private key, certificate and
CA certs of the server in PFX or PKCS12 format. (Mutually exclusive with
the <code>key</code>, <code>cert</code> and <code>ca</code> options.)</p>
</li>
<li><p><code>key</code>: A string or <code>Buffer</code> containing the private key of the server in
PEM format. To support multiple keys using different algorithms, an array
can be provided. It can either be a plain array of keys, or an array of
objects in the format <code>{pem: key, passphrase: passphrase}</code>. (Required)</p>
</li>
<li><p><code>passphrase</code>: A string of passphrase for the private key or pfx.</p>
</li>
<li><p><code>cert</code>: A string or <code>Buffer</code> containing the certificate key of the server in
PEM format. (Could be an array of certs). (Required)</p>
</li>
<li><p><code>ca</code>: A string, <code>Buffer</code> or array of strings or <code>Buffer</code>s of trusted
certificates in PEM format. If this is omitted several well known "root"
CAs will be used, like VeriSign. These are used to authorize connections.</p>
</li>
<li><p><code>crl</code> : Either a string or list of strings of PEM encoded CRLs (Certificate
Revocation List)</p>
</li>
<li><p><code>ciphers</code>: A string describing the ciphers to use or exclude, separated by
<code>:</code>. The default cipher suite is:</p>
<pre><code class="lang-js">ECDHE-RSA-AES128-GCM-SHA256:
ECDHE-ECDSA-AES128-GCM-SHA256:
ECDHE-RSA-AES256-GCM-SHA384:
ECDHE-ECDSA-AES256-GCM-SHA384:
DHE-RSA-AES128-GCM-SHA256:
ECDHE-RSA-AES128-SHA256:
DHE-RSA-AES128-SHA256:
ECDHE-RSA-AES256-SHA384:
DHE-RSA-AES256-SHA384:
ECDHE-RSA-AES256-SHA256:
DHE-RSA-AES256-SHA256:
HIGH:
!aNULL:
!eNULL:
!EXPORT:
!DES:
!RC4:
!MD5:
!PSK:
!SRP:
!CAMELLIA
</code></pre>
<p>The default cipher suite prefers GCM ciphers for <a href="https://www.chromium.org/Home/chromium-security/education/tls#TOC-Deprecation-of-TLS-Features-Algorithms-in-Chrome">Chrome's 'modern
cryptography' setting</a> and also prefers ECDHE and DHE ciphers for Perfect
Forward secrecy, while offering <em>some</em> backward compatibiltity.</p>
<p>128 bit AES is preferred over 192 and 256 bit AES in light of <a href="https://www.schneier.com/blog/archives/2009/07/another_new_aes.html">specific
attacks affecting larger AES key sizes</a>.</p>
<p>Old clients that rely on insecure and deprecated RC4 or DES-based ciphers
(like Internet Explorer 6) aren't able to complete the handshake with the default
configuration. If you absolutely must support these clients, the
<a href="https://wiki.mozilla.org/Security/Server_Side_TLS">TLS recommendations</a> may offer a compatible cipher suite. For more details
on the format, see the <a href="https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT">OpenSSL cipher list format documentation</a>.</p>
</li>
<li><p><code>ecdhCurve</code>: A string describing a named curve to use for ECDH key agreement
or false to disable ECDH.</p>
<p>Defaults to <code>prime256v1</code> (NIST P-256). Use <a href="crypto.html#crypto_crypto_getcurves"><code>crypto.getCurves()</code></a> to obtain
a list of available curve names. On recent releases,
<code>openssl ecparam -list_curves</code> will also display the name and description of
each available elliptic curve.</p>
</li>
<li><p><code>dhparam</code>: A string or <code>Buffer</code> containing Diffie Hellman parameters,
required for Perfect Forward Secrecy. Use <code>openssl dhparam</code> to create it.
Its key length should be greater than or equal to 1024 bits, otherwise
it throws an error. It is strongly recommended to use 2048 bits or
more for stronger security. If omitted or invalid, it is silently
discarded and DHE ciphers won't be available.</p>
</li>
<li><p><code>handshakeTimeout</code>: Abort the connection if the SSL/TLS handshake does not
finish in this many milliseconds. The default is 120 seconds.</p>
<p>A <code>'clientError'</code> is emitted on the <code>tls.Server</code> object whenever a handshake
times out.</p>
</li>
<li><p><code>honorCipherOrder</code> : When choosing a cipher, use the server's preferences
instead of the client preferences. Default: <code>true</code>.</p>
</li>
<li><p><code>requestCert</code>: If <code>true</code> the server will request a certificate from
clients that connect and attempt to verify that certificate. Default:
<code>false</code>.</p>
</li>
<li><p><code>rejectUnauthorized</code>: If <code>true</code> the server will reject any connection
which is not authorized with the list of supplied CAs. This option only
has an effect if <code>requestCert</code> is <code>true</code>. Default: <code>false</code>.</p>
</li>
<li><p><code>NPNProtocols</code>: An array or <code>Buffer</code> of possible NPN protocols. (Protocols
should be ordered by their priority).</p>
</li>
<li><p><code>ALPNProtocols</code>: An array or <code>Buffer</code> of possible ALPN
protocols. (Protocols should be ordered by their priority). When
the server receives both NPN and ALPN extensions from the client,
ALPN takes precedence over NPN and the server does not send an NPN
extension to the client.</p>
</li>
<li><p><code>SNICallback(servername, cb)</code>: A function that will be called if client
supports SNI TLS extension. Two argument will be passed to it: <code>servername</code>,
and <code>cb</code>. <code>SNICallback</code> should invoke <code>cb(null, ctx)</code>, where <code>ctx</code> is a
SecureContext instance.
(You can use <code>tls.createSecureContext(...)</code> to get proper
SecureContext). If <code>SNICallback</code> wasn't provided the default callback with
high-level API will be used (see below).</p>
</li>
<li><p><code>sessionTimeout</code>: An integer specifying the seconds after which TLS
session identifiers and TLS session tickets created by the server are
timed out. See <a href="https://www.openssl.org/docs/ssl/SSL_CTX_set_timeout.html">SSL_CTX_set_timeout</a> for more details.</p>
</li>
<li><p><code>ticketKeys</code>: A 48-byte <code>Buffer</code> instance consisting of 16-byte prefix,
16-byte hmac key, 16-byte AES key. You could use it to accept tls session
tickets on multiple instances of tls server.</p>
<p>NOTE: Automatically shared between <code>cluster</code> module workers.</p>
</li>
<li><p><code>sessionIdContext</code>: A string containing an opaque identifier for session
resumption. If <code>requestCert</code> is <code>true</code>, the default is MD5 hash value
generated from command-line. (In FIPS mode a truncated SHA1 hash is
used instead.) Otherwise, the default is not provided.</p>
</li>
<li><p><code>secureProtocol</code>: The SSL method to use, e.g. <code>SSLv3_method</code> to force
SSL version 3. The possible values depend on your installation of
OpenSSL and are defined in the constant <a href="https://www.openssl.org/docs/ssl/ssl.html#DEALING-WITH-PROTOCOL-METHODS">SSL_METHODS</a>.</p>
</li>
</ul>
<p>Here is a simple example echo server:</p>
<pre><code class="lang-js">const tls = require('tls');
const fs = require('fs');
const options = {
key: fs.readFileSync('server-key.pem'),
cert: fs.readFileSync('server-cert.pem'),
// This is necessary only if using the client certificate authentication.
requestCert: true,
// This is necessary only if the client uses the self-signed certificate.
ca: [ fs.readFileSync('client-cert.pem') ]
};
var server = tls.createServer(options, (socket) => {
console.log('server connected',
socket.authorized ? 'authorized' : 'unauthorized');
socket.write('welcome!\n');
socket.setEncoding('utf8');
socket.pipe(socket);
});
server.listen(8000, () => {
console.log('server bound');
});
</code></pre>
<p>Or</p>
<pre><code class="lang-js">const tls = require('tls');
const fs = require('fs');
const options = {
pfx: fs.readFileSync('server.pfx'),
// This is necessary only if using the client certificate authentication.
requestCert: true,
};
var server = tls.createServer(options, (socket) => {
console.log('server connected',
socket.authorized ? 'authorized' : 'unauthorized');
socket.write('welcome!\n');
socket.setEncoding('utf8');
socket.pipe(socket);
});
server.listen(8000, () => {
console.log('server bound');
});
</code></pre>
<p>You can test this server by connecting to it with <code>openssl s_client</code>:</p>
<pre><code>openssl s_client -connect 127.0.0.1:8000
</code></pre><h2>tls.getCiphers()<span><a class="mark" href="#tls_tls_getciphers" id="tls_tls_getciphers">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.10.2</span>
</div><p>Returns an array with the names of the supported SSL ciphers.</p>
<p>Example:</p>
<pre><code class="lang-js">var ciphers = tls.getCiphers();
console.log(ciphers); // ['AES128-SHA', 'AES256-SHA', ...]
</code></pre>
<!-- [end-include:tls.md] -->
<!-- [start-include:tty.md] -->
<h1>TTY<span><a class="mark" href="#tty_tty" id="tty_tty">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>The <code>tty</code> module houses the <code>tty.ReadStream</code> and <code>tty.WriteStream</code> classes. In
most cases, you will not need to use this module directly.</p>
<p>When Node.js detects that it is being run inside a TTY context, then <code>process.stdin</code>
will be a <code>tty.ReadStream</code> instance and <code>process.stdout</code> will be
a <code>tty.WriteStream</code> instance. The preferred way to check if Node.js is being run
in a TTY context is to check <code>process.stdout.isTTY</code>:</p>
<pre><code>$ node -p -e "Boolean(process.stdout.isTTY)"
true
$ node -p -e "Boolean(process.stdout.isTTY)" | cat
false
</code></pre><h2>Class: ReadStream<span><a class="mark" href="#tty_class_readstream" id="tty_class_readstream">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>A <code>net.Socket</code> subclass that represents the readable portion of a tty. In normal
circumstances, <code>process.stdin</code> will be the only <code>tty.ReadStream</code> instance in any
Node.js program (only when <code>isatty(0)</code> is true).</p>
<h3>rs.isRaw<span><a class="mark" href="#tty_rs_israw" id="tty_rs_israw">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>A <code>Boolean</code> that is initialized to <code>false</code>. It represents the current "raw" state
of the <code>tty.ReadStream</code> instance.</p>
<h3>rs.setRawMode(mode)<span><a class="mark" href="#tty_rs_setrawmode_mode" id="tty_rs_setrawmode_mode">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p><code>mode</code> should be <code>true</code> or <code>false</code>. This sets the properties of the
<code>tty.ReadStream</code> to act either as a raw device or default. <code>isRaw</code> will be set
to the resulting mode.</p>
<h2>Class: WriteStream<span><a class="mark" href="#tty_class_writestream" id="tty_class_writestream">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>A <code>net.Socket</code> subclass that represents the writable portion of a tty. In normal
circumstances, <code>process.stdout</code> will be the only <code>tty.WriteStream</code> instance
ever created (and only when <code>isatty(1)</code> is true).</p>
<h3>Event: 'resize'<span><a class="mark" href="#tty_event_resize" id="tty_event_resize">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p><code>function () {}</code></p>
<p>Emitted by <code>refreshSize()</code> when either of the <code>columns</code> or <code>rows</code> properties
has changed.</p>
<pre><code class="lang-js">process.stdout.on('resize', () => {
console.log('screen size has changed!');
console.log(`${process.stdout.columns}x${process.stdout.rows}`);
});
</code></pre>
<h3>ws.columns<span><a class="mark" href="#tty_ws_columns" id="tty_ws_columns">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>A <code>Number</code> that gives the number of columns the TTY currently has. This property
gets updated on <code>'resize'</code> events.</p>
<h3>ws.rows<span><a class="mark" href="#tty_ws_rows" id="tty_ws_rows">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.7</span>
</div><p>A <code>Number</code> that gives the number of rows the TTY currently has. This property
gets updated on <code>'resize'</code> events.</p>
<h2>tty.isatty(fd)<span><a class="mark" href="#tty_tty_isatty_fd" id="tty_tty_isatty_fd">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Returns <code>true</code> or <code>false</code> depending on if the <code>fd</code> is associated with a
terminal.</p>
<h2>tty.setRawMode(mode)<span><a class="mark" href="#tty_tty_setrawmode_mode" id="tty_tty_setrawmode_mode">#</a></span></h2>
<pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="#tty_rs_setrawmode_mode">tty.ReadStream#setRawMode</a> (i.e. process.stdin.setRawMode) instead.</pre><!-- [end-include:tty.md] -->
<!-- [start-include:url.md] -->
<h1>URL<span><a class="mark" href="#url_url" id="url_url">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>This module has utilities for URL resolution and parsing.
Call <code>require('url')</code> to use it.</p>
<h2>URL Parsing<span><a class="mark" href="#url_url_parsing" id="url_url_parsing">#</a></span></h2>
<p>Parsed URL objects have some or all of the following fields, depending on
whether or not they exist in the URL string. Any parts that are not in the URL
string will not be in the parsed object. Examples are shown for the URL</p>
<p><code>'http://user:pass@host.com:8080/p/a/t/h?query=string#hash'</code></p>
<ul>
<li><p><code>href</code>: The full URL that was originally parsed. Both the protocol and host are lowercased.</p>
<p> Example: <code>'http://user:pass@host.com:8080/p/a/t/h?query=string#hash'</code></p>
</li>
<li><p><code>protocol</code>: The request protocol, lowercased.</p>
<p> Example: <code>'http:'</code></p>
</li>
<li><p><code>slashes</code>: The protocol requires slashes after the colon.</p>
<p> Example: true or false</p>
</li>
<li><p><code>host</code>: The full lowercased host portion of the URL, including port
information.</p>
<p> Example: <code>'host.com:8080'</code></p>
</li>
<li><p><code>auth</code>: The authentication information portion of a URL.</p>
<p> Example: <code>'user:pass'</code></p>
</li>
<li><p><code>hostname</code>: Just the lowercased hostname portion of the host.</p>
<p> Example: <code>'host.com'</code></p>
</li>
<li><p><code>port</code>: The port number portion of the host.</p>
<p> Example: <code>'8080'</code></p>
</li>
<li><p><code>pathname</code>: The path section of the URL, that comes after the host and
before the query, including the initial slash if present. No decoding is
performed.</p>
<p> Example: <code>'/p/a/t/h'</code></p>
</li>
<li><p><code>search</code>: The 'query string' portion of the URL, including the leading
question mark.</p>
<p> Example: <code>'?query=string'</code></p>
</li>
<li><p><code>path</code>: Concatenation of <code>pathname</code> and <code>search</code>. No decoding is performed.</p>
<p> Example: <code>'/p/a/t/h?query=string'</code></p>
</li>
<li><p><code>query</code>: Either the 'params' portion of the query string, or a
querystring-parsed object.</p>
<p> Example: <code>'query=string'</code> or <code>{'query':'string'}</code></p>
</li>
<li><p><code>hash</code>: The 'fragment' portion of the URL including the pound-sign.</p>
<p> Example: <code>'#hash'</code></p>
</li>
</ul>
<h3>Escaped Characters<span><a class="mark" href="#url_escaped_characters" id="url_escaped_characters">#</a></span></h3>
<p>Spaces (<code>' '</code>) and the following characters will be automatically escaped in the
properties of URL objects:</p>
<pre><code>< > " ` \r \n \t { } | \ ^ '
</code></pre><hr>
<p>The following methods are provided by the URL module:</p>
<h2>url.format(urlObj)<span><a class="mark" href="#url_url_format_urlobj" id="url_url_format_urlobj">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>Take a parsed URL object, and return a formatted URL string.</p>
<p>Here's how the formatting process works:</p>
<ul>
<li><code>href</code> will be ignored.</li>
<li><code>path</code> will be ignored.</li>
<li><code>protocol</code> is treated the same with or without the trailing <code>:</code> (colon).<ul>
<li>The protocols <code>http</code>, <code>https</code>, <code>ftp</code>, <code>gopher</code>, <code>file</code> will be
postfixed with <code>://</code> (colon-slash-slash) as long as <code>host</code>/<code>hostname</code> are present.</li>
<li>All other protocols <code>mailto</code>, <code>xmpp</code>, <code>aim</code>, <code>sftp</code>, <code>foo</code>, etc will
be postfixed with <code>:</code> (colon).</li>
</ul>
</li>
<li><code>slashes</code> set to <code>true</code> if the protocol requires <code>://</code> (colon-slash-slash)<ul>
<li>Only needs to be set for protocols not previously listed as requiring
slashes, such as <code>mongodb://localhost:8000/</code>, or if <code>host</code>/<code>hostname</code> are absent.</li>
</ul>
</li>
<li><code>auth</code> will be used if present.</li>
<li><code>hostname</code> will only be used if <code>host</code> is absent.</li>
<li><code>port</code> will only be used if <code>host</code> is absent.</li>
<li><code>host</code> will be used in place of <code>hostname</code> and <code>port</code>.</li>
<li><code>pathname</code> is treated the same with or without the leading <code>/</code> (slash).</li>
<li><code>query</code> (object; see <code>querystring</code>) will only be used if <code>search</code> is absent.</li>
<li><code>search</code> will be used in place of <code>query</code>.<ul>
<li>It is treated the same with or without the leading <code>?</code> (question mark).</li>
</ul>
</li>
<li><code>hash</code> is treated the same with or without the leading <code>#</code> (pound sign, anchor).</li>
</ul>
<h2>url.parse(urlStr[, parseQueryString][, slashesDenoteHost])<span><a class="mark" href="#url_url_parse_urlstr_parsequerystring_slashesdenotehost" id="url_url_parse_urlstr_parsequerystring_slashesdenotehost">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>Take a URL string, and return an object.</p>
<p>Pass <code>true</code> as the second argument to also parse the query string using the
<code>querystring</code> module. If <code>true</code> then the <code>query</code> property will always be
assigned an object, and the <code>search</code> property will always be a (possibly
empty) string. If <code>false</code> then the <code>query</code> property will not be parsed or
decoded. Defaults to <code>false</code>.</p>
<p>Pass <code>true</code> as the third argument to treat <code>//foo/bar</code> as
<code>{ host: 'foo', pathname: '/bar' }</code> rather than
<code>{ pathname: '//foo/bar' }</code>. Defaults to <code>false</code>.</p>
<h2>url.resolve(from, to)<span><a class="mark" href="#url_url_resolve_from_to" id="url_url_resolve_from_to">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.25</span>
</div><p>Take a base URL, and a href URL, and resolve them as a browser would for
an anchor tag. Examples:</p>
<pre><code class="lang-js">url.resolve('/one/two/three', 'four') // '/one/two/four'
url.resolve('http://example.com/', '/one') // 'http://example.com/one'
url.resolve('http://example.com/one', '/two') // 'http://example.com/two'
</code></pre>
<!-- [end-include:url.md] -->
<!-- [start-include:util.md] -->
<h1>Util<span><a class="mark" href="#util_util" id="util_util">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>These functions are in the module <code>'util'</code>. Use <code>require('util')</code> to
access them.</p>
<p>The <code>util</code> module is primarily designed to support the needs of Node.js's
internal APIs. Many of these utilities are useful for your own
programs. If you find that these functions are lacking for your
purposes, however, you are encouraged to write your own utilities. We
are not interested in any future additions to the <code>util</code> module that
are unnecessary for Node.js's internal functionality.</p>
<h2>util.debug(string)<span><a class="mark" href="#util_util_debug_string" id="util_util_debug_string">#</a></span></h2>
<pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="console.html#console_console_error_data"><code>console.error()</code></a> instead.</pre><p>Deprecated predecessor of <code>console.error</code>.</p>
<h2>util.debuglog(section)<span><a class="mark" href="#util_util_debuglog_section" id="util_util_debuglog_section">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.3</span>
</div><ul>
<li><code>section</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><String></a> The section of the program to be debugged</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The logging function</li>
</ul>
<p>This is used to create a function which conditionally writes to stderr
based on the existence of a <code>NODE_DEBUG</code> environment variable. If the
<code>section</code> name appears in that environment variable, then the returned
function will be similar to <code>console.error()</code>. If not, then the
returned function is a no-op.</p>
<p>For example:</p>
<pre><code class="lang-js">var debuglog = util.debuglog('foo');
var bar = 123;
debuglog('hello from foo [%d]', bar);
</code></pre>
<p>If this program is run with <code>NODE_DEBUG=foo</code> in the environment, then
it will output something like:</p>
<pre><code>FOO 3245: hello from foo [123]
</code></pre><p>where <code>3245</code> is the process id. If it is not run with that
environment variable set, then it will not print anything.</p>
<p>You may separate multiple <code>NODE_DEBUG</code> environment variables with a
comma. For example, <code>NODE_DEBUG=fs,net,tls</code>.</p>
<h2>util.deprecate(function, string)<span><a class="mark" href="#util_util_deprecate_function_string" id="util_util_deprecate_function_string">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.8.0</span>
</div><p>Marks that a method should not be used any more.</p>
<pre><code class="lang-js">const util = require('util');
exports.puts = util.deprecate(function() {
for (var i = 0, len = arguments.length; i < len; ++i) {
process.stdout.write(arguments[i] + '\n');
}
}, 'util.puts: Use console.log instead');
</code></pre>
<p>It returns a modified function which warns once by default.</p>
<p>If <code>--no-deprecation</code> is set then this function is a NO-OP. Configurable
at run-time through the <code>process.noDeprecation</code> boolean (only effective
when set before a module is loaded.)</p>
<p>If <code>--trace-deprecation</code> is set, a warning and a stack trace are logged
to the console the first time the deprecated API is used. Configurable
at run-time through the <code>process.traceDeprecation</code> boolean.</p>
<p>If <code>--throw-deprecation</code> is set then the application throws an exception
when the deprecated API is used. Configurable at run-time through the
<code>process.throwDeprecation</code> boolean.</p>
<p><code>process.throwDeprecation</code> takes precedence over <code>process.traceDeprecation</code>.</p>
<h2>util.error([...])<span><a class="mark" href="#util_util_error" id="util_util_error">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
<span>Deprecated since: v0.11.3 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="console.html#console_console_error_data"><code>console.error()</code></a> instead.</pre><p>Deprecated predecessor of <code>console.error</code>.</p>
<h2>util.format(format[, ...])<span><a class="mark" href="#util_util_format_format" id="util_util_format_format">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.3</span>
</div><p>Returns a formatted string using the first argument as a <code>printf</code>-like format.</p>
<p>The first argument is a string that contains zero or more <em>placeholders</em>.
Each placeholder is replaced with the converted value from its corresponding
argument. Supported placeholders are:</p>
<ul>
<li><code>%s</code> - String.</li>
<li><code>%d</code> - Number (both integer and float).</li>
<li><code>%j</code> - JSON. Replaced with the string <code>'[Circular]'</code> if the argument
contains circular references.</li>
<li><code>%%</code> - single percent sign (<code>'%'</code>). This does not consume an argument.</li>
</ul>
<p>If the placeholder does not have a corresponding argument, the placeholder is
not replaced.</p>
<pre><code class="lang-js">util.format('%s:%s', 'foo'); // 'foo:%s'
</code></pre>
<p>If there are more arguments than placeholders, the extra arguments are
coerced to strings (for objects and symbols, <code>util.inspect()</code> is used)
and then concatenated, delimited by a space.</p>
<pre><code class="lang-js">util.format('%s:%s', 'foo', 'bar', 'baz'); // 'foo:bar baz'
</code></pre>
<p>If the first argument is not a format string then <code>util.format()</code> returns
a string that is the concatenation of all its arguments separated by spaces.
Each argument is converted to a string with <code>util.inspect()</code>.</p>
<pre><code class="lang-js">util.format(1, 2, 3); // '1 2 3'
</code></pre>
<h2>util.inherits(constructor, superConstructor)<span><a class="mark" href="#util_util_inherits_constructor_superconstructor" id="util_util_inherits_constructor_superconstructor">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>Inherit the prototype methods from one <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/constructor">constructor</a> into another. The
prototype of <code>constructor</code> will be set to a new object created from
<code>superConstructor</code>.</p>
<p>As an additional convenience, <code>superConstructor</code> will be accessible
through the <code>constructor.super_</code> property.</p>
<pre><code class="lang-js">const util = require('util');
const EventEmitter = require('events');
function MyStream() {
EventEmitter.call(this);
}
util.inherits(MyStream, EventEmitter);
MyStream.prototype.write = function(data) {
this.emit('data', data);
}
var stream = new MyStream();
console.log(stream instanceof EventEmitter); // true
console.log(MyStream.super_ === EventEmitter); // true
stream.on('data', (data) => {
console.log(`Received data: "${data}"`);
})
stream.write('It works!'); // Received data: "It works!"
</code></pre>
<h2>util.inspect(object[, options])<span><a class="mark" href="#util_util_inspect_object_options" id="util_util_inspect_object_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
</div><p>Return a string representation of <code>object</code>, which is useful for debugging.</p>
<p>An optional <em>options</em> object may be passed that alters certain aspects of the
formatted string:</p>
<ul>
<li><p><code>showHidden</code> - if <code>true</code> then the object's non-enumerable and symbol
properties will be shown too. Defaults to <code>false</code>.</p>
</li>
<li><p><code>depth</code> - tells <code>inspect</code> how many times to recurse while formatting the
object. This is useful for inspecting large complicated objects. Defaults to
<code>2</code>. To make it recurse indefinitely pass <code>null</code>.</p>
</li>
<li><p><code>colors</code> - if <code>true</code>, then the output will be styled with ANSI color codes.
Defaults to <code>false</code>. Colors are customizable, see <a href="#util_customizing_util_inspect_colors">Customizing
<code>util.inspect</code> colors</a>.</p>
</li>
<li><p><code>customInspect</code> - if <code>false</code>, then custom <code>inspect(depth, opts)</code> functions
defined on the objects being inspected won't be called. Defaults to <code>true</code>.</p>
</li>
</ul>
<p>Example of inspecting all properties of the <code>util</code> object:</p>
<pre><code class="lang-js">const util = require('util');
console.log(util.inspect(util, { showHidden: true, depth: null }));
</code></pre>
<p>Values may supply their own custom <code>inspect(depth, opts)</code> functions, when
called they receive the current depth in the recursive inspection, as well as
the options object passed to <code>util.inspect()</code>.</p>
<h3>Customizing <code>util.inspect</code> colors<span><a class="mark" href="#util_customizing_util_inspect_colors" id="util_customizing_util_inspect_colors">#</a></span></h3>
<!-- type=misc -->
<p>Color output (if enabled) of <code>util.inspect</code> is customizable globally
via <code>util.inspect.styles</code> and <code>util.inspect.colors</code> objects.</p>
<p><code>util.inspect.styles</code> is a map assigning each style a color
from <code>util.inspect.colors</code>.
Highlighted styles and their default values are:</p>
<ul>
<li><code>number</code> (yellow)</li>
<li><code>boolean</code> (yellow)</li>
<li><code>string</code> (green)</li>
<li><code>date</code> (magenta)</li>
<li><code>regexp</code> (red)</li>
<li><code>null</code> (bold)</li>
<li><code>undefined</code> (grey)</li>
<li><code>special</code> - only function at this time (cyan)</li>
<li><code>name</code> (intentionally no styling)</li>
</ul>
<p>Predefined color codes are: <code>white</code>, <code>grey</code>, <code>black</code>, <code>blue</code>, <code>cyan</code>,
<code>green</code>, <code>magenta</code>, <code>red</code> and <code>yellow</code>.
There are also <code>bold</code>, <code>italic</code>, <code>underline</code> and <code>inverse</code> codes.</p>
<h3>Custom <code>inspect()</code> function on Objects<span><a class="mark" href="#util_custom_inspect_function_on_objects" id="util_custom_inspect_function_on_objects">#</a></span></h3>
<!-- type=misc -->
<p>Objects also may define their own <code>inspect(depth)</code> function which <code>util.inspect()</code>
will invoke and use the result of when inspecting the object:</p>
<pre><code class="lang-js">const util = require('util');
var obj = { name: 'nate' };
obj.inspect = function(depth) {
return `{${this.name}}`;
};
util.inspect(obj);
// "{nate}"
</code></pre>
<p>You may also return another Object entirely, and the returned String will be
formatted according to the returned Object. This is similar to how
<code>JSON.stringify()</code> works:</p>
<pre><code class="lang-js">var obj = { foo: 'this will not show up in the inspect() output' };
obj.inspect = function(depth) {
return { bar: 'baz' };
};
util.inspect(obj);
// "{ bar: 'baz' }"
</code></pre>
<h2>util.isArray(object)<span><a class="mark" href="#util_util_isarray_object" id="util_util_isarray_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Internal alias for <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray"><code>Array.isArray</code></a>.</p>
<p>Returns <code>true</code> if the given "object" is an <code>Array</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isArray([])
// true
util.isArray(new Array)
// true
util.isArray({})
// false
</code></pre>
<h2>util.isBoolean(object)<span><a class="mark" href="#util_util_isboolean_object" id="util_util_isboolean_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is a <code>Boolean</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isBoolean(1)
// false
util.isBoolean(0)
// false
util.isBoolean(false)
// true
</code></pre>
<h2>util.isBuffer(object)<span><a class="mark" href="#util_util_isbuffer_object" id="util_util_isbuffer_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="buffer.html#buffer_class_method_buffer_isbuffer_obj"><code>Buffer.isBuffer()</code></a> instead.</pre><p>Returns <code>true</code> if the given "object" is a <code>Buffer</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isBuffer({ length: 0 })
// false
util.isBuffer([])
// false
util.isBuffer(new Buffer('hello world'))
// true
</code></pre>
<h2>util.isDate(object)<span><a class="mark" href="#util_util_isdate_object" id="util_util_isdate_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is a <code>Date</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isDate(new Date())
// true
util.isDate(Date())
// false (without 'new' returns a String)
util.isDate({})
// false
</code></pre>
<h2>util.isError(object)<span><a class="mark" href="#util_util_iserror_object" id="util_util_iserror_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is an <a href="errors.html#errors_class_error"><code>Error</code></a>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isError(new Error())
// true
util.isError(new TypeError())
// true
util.isError({ name: 'Error', message: 'an error occurred' })
// false
</code></pre>
<h2>util.isFunction(object)<span><a class="mark" href="#util_util_isfunction_object" id="util_util_isfunction_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is a <code>Function</code>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
function Foo() {}
var Bar = function() {};
util.isFunction({})
// false
util.isFunction(Foo)
// true
util.isFunction(Bar)
// true
</code></pre>
<h2>util.isNull(object)<span><a class="mark" href="#util_util_isnull_object" id="util_util_isnull_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is strictly <code>null</code>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isNull(0)
// false
util.isNull(undefined)
// false
util.isNull(null)
// true
</code></pre>
<h2>util.isNullOrUndefined(object)<span><a class="mark" href="#util_util_isnullorundefined_object" id="util_util_isnullorundefined_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is <code>null</code> or <code>undefined</code>. Otherwise,
returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isNullOrUndefined(0)
// false
util.isNullOrUndefined(undefined)
// true
util.isNullOrUndefined(null)
// true
</code></pre>
<h2>util.isNumber(object)<span><a class="mark" href="#util_util_isnumber_object" id="util_util_isnumber_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is a <code>Number</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isNumber(false)
// false
util.isNumber(Infinity)
// true
util.isNumber(0)
// true
util.isNumber(NaN)
// true
</code></pre>
<h2>util.isObject(object)<span><a class="mark" href="#util_util_isobject_object" id="util_util_isobject_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is strictly an <code>Object</code> <strong>and</strong> not a
<code>Function</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isObject(5)
// false
util.isObject(null)
// false
util.isObject({})
// true
util.isObject(function(){})
// false
</code></pre>
<h2>util.isPrimitive(object)<span><a class="mark" href="#util_util_isprimitive_object" id="util_util_isprimitive_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is a primitive type. Otherwise, returns
<code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isPrimitive(5)
// true
util.isPrimitive('foo')
// true
util.isPrimitive(false)
// true
util.isPrimitive(null)
// true
util.isPrimitive(undefined)
// true
util.isPrimitive({})
// false
util.isPrimitive(function() {})
// false
util.isPrimitive(/^$/)
// false
util.isPrimitive(new Date())
// false
</code></pre>
<h2>util.isRegExp(object)<span><a class="mark" href="#util_util_isregexp_object" id="util_util_isregexp_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is a <code>RegExp</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isRegExp(/some regexp/)
// true
util.isRegExp(new RegExp('another regexp'))
// true
util.isRegExp({})
// false
</code></pre>
<h2>util.isString(object)<span><a class="mark" href="#util_util_isstring_object" id="util_util_isstring_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is a <code>String</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isString('')
// true
util.isString('foo')
// true
util.isString(String('foo'))
// true
util.isString(5)
// false
</code></pre>
<h3>util.isSymbol(object)<span><a class="mark" href="#util_util_issymbol_object" id="util_util_issymbol_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is a <code>Symbol</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
util.isSymbol(5)
// false
util.isSymbol('foo')
// false
util.isSymbol(Symbol('foo'))
// true
</code></pre>
<h2>util.isUndefined(object)<span><a class="mark" href="#util_util_isundefined_object" id="util_util_isundefined_object">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.5</span>
<span>Deprecated since: v4.0.0 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated</pre><p>Returns <code>true</code> if the given "object" is <code>undefined</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="lang-js">const util = require('util');
var foo;
util.isUndefined(5)
// false
util.isUndefined(foo)
// true
util.isUndefined(null)
// false
</code></pre>
<h2>util.log(string)<span><a class="mark" href="#util_util_log_string" id="util_util_log_string">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
<span>Deprecated since: v6.0.0 </span>
</div><p>Output with timestamp on <code>stdout</code>.</p>
<pre><code>require('util').log('Timestamped message.');
</code></pre><h2>util.print([...])<span><a class="mark" href="#util_util_print" id="util_util_print">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
<span>Deprecated since: v0.11.3 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="console.html#console_console_log_data"><code>console.log()</code></a> instead.</pre><p>Deprecated predecessor of <code>console.log</code>.</p>
<h2>util.pump(readableStream, writableStream[, callback])<span><a class="mark" href="#util_util_pump_readablestream_writablestream_callback" id="util_util_pump_readablestream_writablestream_callback">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
<span>Deprecated since: v0.9.1 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use readableStream.pipe(writableStream)</pre><p>Deprecated predecessor of <code>stream.pipe()</code>.</p>
<h2>util.puts([...])<span><a class="mark" href="#util_util_puts" id="util_util_puts">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.0</span>
<span>Deprecated since: v0.11.3 </span>
</div><pre class="api_stability api_stability_0">Stability: 0 - Deprecated: Use <a href="console.html#console_console_log_data"><code>console.log()</code></a> instead.</pre><p>Deprecated predecessor of <code>console.log</code>.</p>
<!-- [end-include:util.md] -->
<!-- [start-include:v8.md] -->
<h1>V8<span><a class="mark" href="#v8_v8" id="v8_v8">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>This module exposes events and interfaces specific to the version of <a href="https://developers.google.com/v8/">V8</a>
built with Node.js. These interfaces are subject to change by upstream and are
therefore not covered under the stability index.</p>
<h2>getHeapStatistics()<span><a class="mark" href="#v8_getheapstatistics" id="v8_getheapstatistics">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><p>Returns an object with the following properties</p>
<pre><code class="lang-js">{
total_heap_size: 7326976,
total_heap_size_executable: 4194304,
total_physical_size: 7326976,
total_available_size: 1152656,
used_heap_size: 3476208,
heap_size_limit: 1535115264
}
</code></pre>
<h2>getHeapSpaceStatistics()<span><a class="mark" href="#v8_getheapspacestatistics" id="v8_getheapspacestatistics">#</a></span></h2>
<p>Returns statistics about the V8 heap spaces, i.e. the segments which make up
the V8 heap. Order of heap spaces nor availability of a heap space can be
guaranteed as the statistics are provided via the V8 <code>GetHeapSpaceStatistics</code>
function.</p>
<p>Example result:</p>
<pre><code>[
{
"space_name": "new_space",
"space_size": 2063872,
"space_used_size": 951112,
"space_available_size": 80824,
"physical_space_size": 2063872
},
{
"space_name": "old_space",
"space_size": 3090560,
"space_used_size": 2493792,
"space_available_size": 0,
"physical_space_size": 3090560
},
{
"space_name": "code_space",
"space_size": 1260160,
"space_used_size": 644256,
"space_available_size": 960,
"physical_space_size": 1260160
},
{
"space_name": "map_space",
"space_size": 1094160,
"space_used_size": 201608,
"space_available_size": 0,
"physical_space_size": 1094160
},
{
"space_name": "large_object_space",
"space_size": 0,
"space_used_size": 0,
"space_available_size": 1490980608,
"physical_space_size": 0
}
]
</code></pre><h2>setFlagsFromString(string)<span><a class="mark" href="#v8_setflagsfromstring_string" id="v8_setflagsfromstring_string">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v1.0.0</span>
</div><p>Set additional V8 command line flags. Use with care; changing settings
after the VM has started may result in unpredictable behavior, including
crashes and data loss. Or it may simply do nothing.</p>
<p>The V8 options available for a version of Node.js may be determined by running
<code>node --v8-options</code>. An unofficial, community-maintained list of options
and their effects is available <a href="https://github.com/thlorenz/v8-flags/blob/master/flags-0.11.md">here</a>.</p>
<p>Usage:</p>
<pre><code class="lang-js">// Print GC events to stdout for one minute.
const v8 = require('v8');
v8.setFlagsFromString('--trace_gc');
setTimeout(function() { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
</code></pre>
<!-- [end-include:v8.md] -->
<!-- [start-include:vm.md] -->
<h1>VM (Executing JavaScript)<span><a class="mark" href="#vm_vm_executing_javascript" id="vm_vm_executing_javascript">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><!--name=vm-->
<p>You can access this module with:</p>
<pre><code class="lang-js">const vm = require('vm');
</code></pre>
<p>JavaScript code can be compiled and run immediately or compiled, saved, and run
later.</p>
<h2>Class: Script<span><a class="mark" href="#vm_class_script" id="vm_class_script">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.1</span>
</div><p>A class for holding precompiled scripts, and running them in specific sandboxes.</p>
<h3>new vm.Script(code, options)<span><a class="mark" href="#vm_new_vm_script_code_options" id="vm_new_vm_script_code_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.1</span>
</div><p>Creating a new <code>Script</code> compiles <code>code</code> but does not run it. Instead, the
created <code>vm.Script</code> object represents this compiled code. This script can be run
later many times using methods below. The returned script is not bound to any
global object. It is bound before each run, just for that run.</p>
<p>The options when creating a script are:</p>
<ul>
<li><code>filename</code>: allows you to control the filename that shows up in any stack
traces produced from this script.</li>
<li><code>lineOffset</code>: allows you to add an offset to the line number that is
displayed in stack traces</li>
<li><code>columnOffset</code>: allows you to add an offset to the column number that is
displayed in stack traces</li>
<li><code>displayErrors</code>: whether or not to print any errors to stderr, with the
line of code that caused them highlighted, before throwing an exception.
Applies only to syntax errors compiling the code; errors while running the
code are controlled by the options to the script's methods.</li>
<li><code>timeout</code>: a number of milliseconds to execute <code>code</code> before terminating
execution. If execution is terminated, an <a href="errors.html#errors_class_error"><code>Error</code></a> will be thrown.</li>
</ul>
<h3>script.runInContext(contextifiedSandbox[, options])<span><a class="mark" href="#vm_script_runincontext_contextifiedsandbox_options" id="vm_script_runincontext_contextifiedsandbox_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.1</span>
</div><p>Similar to <a href="#vm_vm_runincontext_code_contextifiedsandbox_options"><code>vm.runInContext()</code></a> but a method of a precompiled <code>Script</code>
object. <code>script.runInContext()</code> runs <code>script</code>'s compiled code in
<code>contextifiedSandbox</code> and returns the result. Running code does not have access
to local scope.</p>
<p><code>script.runInContext()</code> takes the same options as
<a href="#vm_script_runinthiscontext_options"><code>script.runInThisContext()</code></a>.</p>
<p>Example: compile code that increments a global variable and sets one, then
execute the code multiple times. These globals are contained in the sandbox.</p>
<pre><code class="lang-js">const util = require('util');
const vm = require('vm');
var sandbox = {
animal: 'cat',
count: 2
};
var context = new vm.createContext(sandbox);
var script = new vm.Script('count += 1; name = "kitty"');
for (var i = 0; i < 10; ++i) {
script.runInContext(context);
}
console.log(util.inspect(sandbox));
// { animal: 'cat', count: 12, name: 'kitty' }
</code></pre>
<p>Note that running untrusted code is a tricky business requiring great care.
<code>script.runInContext()</code> is quite useful, but safely running untrusted code
requires a separate process.</p>
<h3>script.runInNewContext([sandbox][, options])<span><a class="mark" href="#vm_script_runinnewcontext_sandbox_options" id="vm_script_runinnewcontext_sandbox_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.1</span>
</div><p>Similar to <a href="#vm_vm_runinnewcontext_code_sandbox_options"><code>vm.runInNewContext()</code></a> but a method of a precompiled <code>Script</code>
object. <code>script.runInNewContext()</code> contextifies <code>sandbox</code> if passed or creates a
new contextified sandbox if it's omitted, and then runs <code>script</code>'s compiled code
with the sandbox as the global object and returns the result. Running code does
not have access to local scope.</p>
<p><code>script.runInNewContext()</code> takes the same options as
<a href="#vm_script_runinthiscontext_options"><code>script.runInThisContext()</code></a>.</p>
<p>Example: compile code that sets a global variable, then execute the code
multiple times in different contexts. These globals are set on and contained in
the sandboxes.</p>
<pre><code class="lang-js">const util = require('util');
const vm = require('vm');
const sandboxes = [{}, {}, {}];
const script = new vm.Script('globalVar = "set"');
sandboxes.forEach((sandbox) => {
script.runInNewContext(sandbox);
});
console.log(util.inspect(sandboxes));
// [{ globalVar: 'set' }, { globalVar: 'set' }, { globalVar: 'set' }]
</code></pre>
<p>Note that running untrusted code is a tricky business requiring great care.
<code>script.runInNewContext()</code> is quite useful, but safely running untrusted code
requires a separate process.</p>
<h3>script.runInThisContext(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#vm_script_runinthiscontext_options" id="vm_script_runinthiscontext_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.1</span>
</div><p>Similar to <a href=""><code>vm.runInThisContext()</code></a> but a method of a precompiled <code>Script</code>
object. <code>script.runInThisContext()</code> runs <code>script</code>'s compiled code and returns
the result. Running code does not have access to local scope, but does have
access to the current <code>global</code> object.</p>
<p>Example of using <code>script.runInThisContext()</code> to compile code once and run it
multiple times:</p>
<pre><code class="lang-js">const vm = require('vm');
global.globalVar = 0;
const script = new vm.Script('globalVar += 1', { filename: 'myfile.vm' });
for (var i = 0; i < 1000; ++i) {
script.runInThisContext();
}
console.log(globalVar);
// 1000
</code></pre>
<p>The options for running a script are:</p>
<ul>
<li><code>filename</code>: allows you to control the filename that shows up in any stack
traces produced.</li>
<li><code>lineOffset</code>: allows you to add an offset to the line number that is
displayed in stack traces</li>
<li><code>columnOffset</code>: allows you to add an offset to the column number that is
displayed in stack traces</li>
<li><code>displayErrors</code>: whether or not to print any errors to stderr, with the
line of code that caused them highlighted, before throwing an exception.
Applies only to runtime errors executing the code; it is impossible to create
a <code>Script</code> instance with syntax errors, as the constructor will throw.</li>
<li><code>timeout</code>: a number of milliseconds to execute the script before terminating
execution. If execution is terminated, an <a href="errors.html#errors_class_error"><code>Error</code></a> will be thrown.</li>
</ul>
<h2>vm.createContext([sandbox])<span><a class="mark" href="#vm_vm_createcontext_sandbox" id="vm_vm_createcontext_sandbox">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.1</span>
</div><p>If given a <code>sandbox</code> object, will "contextify" that sandbox so that it can be
used in calls to <a href="#vm_vm_runincontext_code_contextifiedsandbox_options"><code>vm.runInContext()</code></a> or <a href="#vm_script_runincontext_contextifiedsandbox_options"><code>script.runInContext()</code></a>. Inside
scripts run as such, <code>sandbox</code> will be the global object, retaining all its
existing properties but also having the built-in objects and functions any
standard <a href="https://es5.github.io/#x15.1">global object</a> has. Outside of scripts run by the vm module,
<code>sandbox</code> will be unchanged.</p>
<p>If not given a sandbox object, returns a new, empty contextified sandbox object
you can use.</p>
<p>This function is useful for creating a sandbox that can be used to run multiple
scripts, e.g. if you were emulating a web browser it could be used to create a
single sandbox representing a window's global object, then run all <code><script></code>
tags together inside that sandbox.</p>
<h2>vm.isContext(sandbox)<span><a class="mark" href="#vm_vm_iscontext_sandbox" id="vm_vm_iscontext_sandbox">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.7</span>
</div><p>Returns whether or not a sandbox object has been contextified by calling
<a href="#vm_vm_createcontext_sandbox"><code>vm.createContext()</code></a> on it.</p>
<h2>vm.runInContext(code, contextifiedSandbox[, options])<span><a class="mark" href="#vm_vm_runincontext_code_contextifiedsandbox_options" id="vm_vm_runincontext_code_contextifiedsandbox_options">#</a></span></h2>
<p><code>vm.runInContext()</code> compiles <code>code</code>, then runs it in <code>contextifiedSandbox</code> and
returns the result. Running code does not have access to local scope. The
<code>contextifiedSandbox</code> object must have been previously contextified via
<a href="#vm_vm_createcontext_sandbox"><code>vm.createContext()</code></a>; it will be used as the global object for <code>code</code>.</p>
<p><code>vm.runInContext()</code> takes the same options as <a href="#vm_vm_runinthiscontext_code_options"><code>vm.runInThisContext()</code></a>.</p>
<p>Example: compile and execute different scripts in a single existing context.</p>
<pre><code class="lang-js">const util = require('util');
const vm = require('vm');
const sandbox = { globalVar: 1 };
vm.createContext(sandbox);
for (var i = 0; i < 10; ++i) {
vm.runInContext('globalVar *= 2;', sandbox);
}
console.log(util.inspect(sandbox));
// { globalVar: 1024 }
</code></pre>
<p>Note that running untrusted code is a tricky business requiring great care.
<code>vm.runInContext()</code> is quite useful, but safely running untrusted code requires
a separate process.</p>
<h2>vm.runInDebugContext(code)<span><a class="mark" href="#vm_vm_runindebugcontext_code" id="vm_vm_runindebugcontext_code">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.14</span>
</div><p><code>vm.runInDebugContext()</code> compiles and executes <code>code</code> inside the V8 debug
context. The primary use case is to get access to the V8 debug object:</p>
<pre><code class="lang-js">const vm = require('vm');
const Debug = vm.runInDebugContext('Debug');
console.log(Debug.findScript(process.emit).name); // 'events.js'
console.log(Debug.findScript(process.exit).name); // 'internal/process.js'
</code></pre>
<p>Note that the debug context and object are intrinsically tied to V8's debugger
implementation and may change (or even get removed) without prior warning.</p>
<p>The debug object can also be exposed with the <code>--expose_debug_as=</code> switch.</p>
<h2>vm.runInNewContext(code[, sandbox][, options])<span><a class="mark" href="#vm_vm_runinnewcontext_code_sandbox_options" id="vm_vm_runinnewcontext_code_sandbox_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.1</span>
</div><p><code>vm.runInNewContext()</code> compiles <code>code</code>, contextifies <code>sandbox</code> if passed or
creates a new contextified sandbox if it's omitted, and then runs the code with
the sandbox as the global object and returns the result.</p>
<p><code>vm.runInNewContext()</code> takes the same options as <a href="#vm_vm_runinthiscontext_code_options"><code>vm.runInThisContext()</code></a>.</p>
<p>Example: compile and execute code that increments a global variable and sets a
new one. These globals are contained in the sandbox.</p>
<pre><code class="lang-js">const util = require('util');
const vm = require('vm');
const sandbox = {
animal: 'cat',
count: 2
};
vm.runInNewContext('count += 1; name = "kitty"', sandbox);
console.log(util.inspect(sandbox));
// { animal: 'cat', count: 3, name: 'kitty' }
</code></pre>
<p>Note that running untrusted code is a tricky business requiring great care.
<code>vm.runInNewContext()</code> is quite useful, but safely running untrusted code requires
a separate process.</p>
<h2>vm.runInThisContext(code[, options])<span><a class="mark" href="#vm_vm_runinthiscontext_code_options" id="vm_vm_runinthiscontext_code_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.3.1</span>
</div><p><code>vm.runInThisContext()</code> compiles <code>code</code>, runs it and returns the result. Running
code does not have access to local scope, but does have access to the current
<code>global</code> object.</p>
<p>Example of using <code>vm.runInThisContext()</code> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval"><code>eval()</code></a> to run the same code:</p>
<pre><code class="lang-js">const vm = require('vm');
var localVar = 'initial value';
const vmResult = vm.runInThisContext('localVar = "vm";');
console.log('vmResult:', vmResult);
console.log('localVar:', localVar);
const evalResult = eval('localVar = "eval";');
console.log('evalResult:', evalResult);
console.log('localVar:', localVar);
// vmResult: 'vm', localVar: 'initial value'
// evalResult: 'eval', localVar: 'eval'
</code></pre>
<p><code>vm.runInThisContext()</code> does not have access to the local scope, so <code>localVar</code>
is unchanged. <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval"><code>eval()</code></a> does have access to the local scope, so <code>localVar</code> is
changed.</p>
<p>In this way <code>vm.runInThisContext()</code> is much like an <a href="https://es5.github.io/#x10.4.2">indirect <code>eval()</code> call</a>,
e.g. <code>(0,eval)('code')</code>. However, it also has the following additional options:</p>
<ul>
<li><code>filename</code>: allows you to control the filename that shows up in any stack
traces produced.</li>
<li><code>lineOffset</code>: allows you to add an offset to the line number that is
displayed in stack traces</li>
<li><code>columnOffset</code>: allows you to add an offset to the column number that is
displayed in stack traces</li>
<li><code>displayErrors</code>: whether or not to print any errors to stderr, with the
line of code that caused them highlighted, before throwing an exception.
Will capture both syntax errors from compiling <code>code</code> and runtime errors
thrown by executing the compiled code. Defaults to <code>true</code>.</li>
<li><code>timeout</code>: a number of milliseconds to execute <code>code</code> before terminating
execution. If execution is terminated, an <a href="errors.html#errors_class_error"><code>Error</code></a> will be thrown.</li>
</ul>
<h2>Example: Run a Server within a VM<span><a class="mark" href="#vm_example_run_a_server_within_a_vm" id="vm_example_run_a_server_within_a_vm">#</a></span></h2>
<p>The context of <code>.runInThisContext()</code> refers to the V8 context. The code passed
to this VM context will have it's own isolated scope. To run a simple web server
using the <code>http</code> module, for instance, the code passed to the context must either
call <code>require('http')</code> on its own, or have a reference to the <code>http</code> module passed
to it. For instance:</p>
<pre><code class="lang-js">'use strict';
const vm = require('vm');
let code =
`(function(require) {
const http = require('http');
http.createServer( (request, response) => {
response.writeHead(200, {'Content-Type': 'text/plain'});
response.end('Hello World\\n');
}).listen(8124);
console.log('Server running at http://127.0.0.1:8124/');
})`;
vm.runInThisContext(code)(require);
</code></pre>
<p><em>Note: <code>require()</code> in the above case shares the state with context it is passed
from. This might introduce risks when unknown code is executed, e.g. altering
objects from the calling thread's context in unwanted ways. It is advisable to
run <code>vm</code> code in a separate process.</em></p>
<!-- [end-include:vm.md] -->
<!-- [start-include:zlib.md] -->
<h1>Zlib<span><a class="mark" href="#zlib_zlib" id="zlib_zlib">#</a></span></h1>
<pre class="api_stability api_stability_2">Stability: 2 - Stable</pre><p>You can access this module with:</p>
<pre><code>const zlib = require('zlib');
</code></pre><p>This provides bindings to Gzip/Gunzip, Deflate/Inflate, and
DeflateRaw/InflateRaw classes. Each class takes the same options, and
is a readable/writable Stream.</p>
<h2>Examples<span><a class="mark" href="#zlib_examples" id="zlib_examples">#</a></span></h2>
<p>Compressing or decompressing a file can be done by piping an
fs.ReadStream into a zlib stream, then into an fs.WriteStream.</p>
<pre><code class="lang-js">const gzip = zlib.createGzip();
const fs = require('fs');
const inp = fs.createReadStream('input.txt');
const out = fs.createWriteStream('input.txt.gz');
inp.pipe(gzip).pipe(out);
</code></pre>
<p>Compressing or decompressing data in one step can be done by using
the convenience methods.</p>
<pre><code class="lang-js">const input = '.................................';
zlib.deflate(input, (err, buffer) => {
if (!err) {
console.log(buffer.toString('base64'));
} else {
// handle error
}
});
const buffer = new Buffer('eJzT0yMAAGTvBe8=', 'base64');
zlib.unzip(buffer, (err, buffer) => {
if (!err) {
console.log(buffer.toString());
} else {
// handle error
}
});
</code></pre>
<p>To use this module in an HTTP client or server, use the <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3">accept-encoding</a>
on requests, and the <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.11">content-encoding</a> header on responses.</p>
<p><strong>Note: these examples are drastically simplified to show
the basic concept.</strong> Zlib encoding can be expensive, and the results
ought to be cached. See <a href="#zlib_memory_usage_tuning">Memory Usage Tuning</a> for more information
on the speed/memory/compression tradeoffs involved in zlib usage.</p>
<pre><code class="lang-js">// client request example
const zlib = require('zlib');
const http = require('http');
const fs = require('fs');
const request = http.get({ host: 'izs.me',
path: '/',
port: 80,
headers: { 'accept-encoding': 'gzip,deflate' } });
request.on('response', (response) => {
var output = fs.createWriteStream('izs.me_index.html');
switch (response.headers['content-encoding']) {
// or, just use zlib.createUnzip() to handle both cases
case 'gzip':
response.pipe(zlib.createGunzip()).pipe(output);
break;
case 'deflate':
response.pipe(zlib.createInflate()).pipe(output);
break;
default:
response.pipe(output);
break;
}
});
// server example
// Running a gzip operation on every request is quite expensive.
// It would be much more efficient to cache the compressed buffer.
const zlib = require('zlib');
const http = require('http');
const fs = require('fs');
http.createServer((request, response) => {
var raw = fs.createReadStream('index.html');
var acceptEncoding = request.headers['accept-encoding'];
if (!acceptEncoding) {
acceptEncoding = '';
}
// Note: this is not a conformant accept-encoding parser.
// See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
if (acceptEncoding.match(/\bdeflate\b/)) {
response.writeHead(200, { 'content-encoding': 'deflate' });
raw.pipe(zlib.createDeflate()).pipe(response);
} else if (acceptEncoding.match(/\bgzip\b/)) {
response.writeHead(200, { 'content-encoding': 'gzip' });
raw.pipe(zlib.createGzip()).pipe(response);
} else {
response.writeHead(200, {});
raw.pipe(response);
}
}).listen(1337);
</code></pre>
<h2>Memory Usage Tuning<span><a class="mark" href="#zlib_memory_usage_tuning" id="zlib_memory_usage_tuning">#</a></span></h2>
<!--type=misc-->
<p>From <code>zlib/zconf.h</code>, modified to node.js's usage:</p>
<p>The memory requirements for deflate are (in bytes):</p>
<pre><code>(1 << (windowBits+2)) + (1 << (memLevel+9))
</code></pre><p>that is: 128K for windowBits=15 + 128K for memLevel = 8
(default values) plus a few kilobytes for small objects.</p>
<p>For example, if you want to reduce
the default memory requirements from 256K to 128K, set the options to:</p>
<pre><code>{ windowBits: 14, memLevel: 7 }
</code></pre><p>Of course this will generally degrade compression (there's no free lunch).</p>
<p>The memory requirements for inflate are (in bytes)</p>
<pre><code>1 << windowBits
</code></pre><p>that is, 32K for windowBits=15 (default value) plus a few kilobytes
for small objects.</p>
<p>This is in addition to a single internal output slab buffer of size
<code>chunkSize</code>, which defaults to 16K.</p>
<p>The speed of zlib compression is affected most dramatically by the
<code>level</code> setting. A higher level will result in better compression, but
will take longer to complete. A lower level will result in less
compression, but will be much faster.</p>
<p>In general, greater memory usage options will mean that node.js has to make
fewer calls to zlib, since it'll be able to process more data in a
single <code>write</code> operation. So, this is another factor that affects the
speed, at the cost of memory usage.</p>
<h2>Flushing<span><a class="mark" href="#zlib_flushing" id="zlib_flushing">#</a></span></h2>
<p>Calling <a href="#zlib_zlib_flush_kind_callback"><code>.flush()</code></a> on a compression stream will make zlib return as much
output as currently possible. This may come at the cost of degraded compression
quality, but can be useful when data needs to be available as soon as possible.</p>
<p>In the following example, <code>flush()</code> is used to write a compressed partial
HTTP response to the client:</p>
<pre><code class="lang-js">const zlib = require('zlib');
const http = require('http');
http.createServer((request, response) => {
// For the sake of simplicity, the Accept-Encoding checks are omitted.
response.writeHead(200, { 'content-encoding': 'gzip' });
const output = zlib.createGzip();
output.pipe(response);
setInterval(() => {
output.write(`The current time is ${Date()}\n`, () => {
// The data has been passed to zlib, but the compression algorithm may
// have decided to buffer the data for more efficient compression.
// Calling .flush() will make the data available as soon as the client
// is ready to receive it.
output.flush();
});
}, 1000);
}).listen(1337);
</code></pre>
<h2>Constants<span><a class="mark" href="#zlib_constants" id="zlib_constants">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><!--type=misc-->
<p>All of the constants defined in zlib.h are also defined on
<code>require('zlib')</code>.
In the normal course of operations, you will not need to ever set any of
these. They are documented here so that their presence is not
surprising. This section is taken almost directly from the
<a href="http://zlib.net/manual.html#Constants">zlib documentation</a>. See <a href="http://zlib.net/manual.html#Constants">http://zlib.net/manual.html#Constants</a> for more
details.</p>
<p>Allowed flush values.</p>
<ul>
<li><code>zlib.Z_NO_FLUSH</code></li>
<li><code>zlib.Z_PARTIAL_FLUSH</code></li>
<li><code>zlib.Z_SYNC_FLUSH</code></li>
<li><code>zlib.Z_FULL_FLUSH</code></li>
<li><code>zlib.Z_FINISH</code></li>
<li><code>zlib.Z_BLOCK</code></li>
<li><code>zlib.Z_TREES</code></li>
</ul>
<p>Return codes for the compression/decompression functions. Negative
values are errors, positive values are used for special but normal
events.</p>
<ul>
<li><code>zlib.Z_OK</code></li>
<li><code>zlib.Z_STREAM_END</code></li>
<li><code>zlib.Z_NEED_DICT</code></li>
<li><code>zlib.Z_ERRNO</code></li>
<li><code>zlib.Z_STREAM_ERROR</code></li>
<li><code>zlib.Z_DATA_ERROR</code></li>
<li><code>zlib.Z_MEM_ERROR</code></li>
<li><code>zlib.Z_BUF_ERROR</code></li>
<li><code>zlib.Z_VERSION_ERROR</code></li>
</ul>
<p>Compression levels.</p>
<ul>
<li><code>zlib.Z_NO_COMPRESSION</code></li>
<li><code>zlib.Z_BEST_SPEED</code></li>
<li><code>zlib.Z_BEST_COMPRESSION</code></li>
<li><code>zlib.Z_DEFAULT_COMPRESSION</code></li>
</ul>
<p>Compression strategy.</p>
<ul>
<li><code>zlib.Z_FILTERED</code></li>
<li><code>zlib.Z_HUFFMAN_ONLY</code></li>
<li><code>zlib.Z_RLE</code></li>
<li><code>zlib.Z_FIXED</code></li>
<li><code>zlib.Z_DEFAULT_STRATEGY</code></li>
</ul>
<p>The deflate compression method (the only one supported in this version).</p>
<ul>
<li><code>zlib.Z_DEFLATED</code></li>
</ul>
<p>For initializing zalloc, zfree, opaque.</p>
<ul>
<li><code>zlib.Z_NULL</code></li>
</ul>
<h2>Class Options<span><a class="mark" href="#zlib_class_options" id="zlib_class_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.1</span>
</div><!--type=misc-->
<p>Each class takes an options object. All options are optional.</p>
<p>Note that some options are only relevant when compressing, and are
ignored by the decompression classes.</p>
<ul>
<li>flush (default: <code>zlib.Z_NO_FLUSH</code>)</li>
<li>chunkSize (default: 16*1024)</li>
<li>windowBits</li>
<li>level (compression only)</li>
<li>memLevel (compression only)</li>
<li>strategy (compression only)</li>
<li>dictionary (deflate/inflate only, empty dictionary by default)</li>
</ul>
<p>See the description of <code>deflateInit2</code> and <code>inflateInit2</code> at
<a href="http://zlib.net/manual.html#Advanced">http://zlib.net/manual.html#Advanced</a> for more information on these.</p>
<h2>Class: zlib.Deflate<span><a class="mark" href="#zlib_class_zlib_deflate" id="zlib_class_zlib_deflate">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Compress data using deflate.</p>
<h2>Class: zlib.DeflateRaw<span><a class="mark" href="#zlib_class_zlib_deflateraw" id="zlib_class_zlib_deflateraw">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Compress data using deflate, and do not append a zlib header.</p>
<h2>Class: zlib.Gunzip<span><a class="mark" href="#zlib_class_zlib_gunzip" id="zlib_class_zlib_gunzip">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Decompress a gzip stream.</p>
<h2>Class: zlib.Gzip<span><a class="mark" href="#zlib_class_zlib_gzip" id="zlib_class_zlib_gzip">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Compress data using gzip.</p>
<h2>Class: zlib.Inflate<span><a class="mark" href="#zlib_class_zlib_inflate" id="zlib_class_zlib_inflate">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Decompress a deflate stream.</p>
<h2>Class: zlib.InflateRaw<span><a class="mark" href="#zlib_class_zlib_inflateraw" id="zlib_class_zlib_inflateraw">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Decompress a raw deflate stream.</p>
<h2>Class: zlib.Unzip<span><a class="mark" href="#zlib_class_zlib_unzip" id="zlib_class_zlib_unzip">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Decompress either a Gzip- or Deflate-compressed stream by auto-detecting
the header.</p>
<h2>Class: zlib.Zlib<span><a class="mark" href="#zlib_class_zlib_zlib" id="zlib_class_zlib_zlib">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Not exported by the <code>zlib</code> module. It is documented here because it is the base
class of the compressor/decompressor classes.</p>
<h3>zlib.flush([kind], callback)<span><a class="mark" href="#zlib_zlib_flush_kind_callback" id="zlib_zlib_flush_kind_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p><code>kind</code> defaults to <code>zlib.Z_FULL_FLUSH</code>.</p>
<p>Flush pending data. Don't call this frivolously, premature flushes negatively
impact the effectiveness of the compression algorithm.</p>
<p>Calling this only flushes data from the internal zlib state, and does not
perform flushing of any kind on the streams level. Rather, it behaves like a
normal call to <code>.write()</code>, i.e. it will be queued up behind other pending
writes and will only produce output when data is being read from the stream.</p>
<h3>zlib.params(level, strategy, callback)<span><a class="mark" href="#zlib_zlib_params_level_strategy_callback" id="zlib_zlib_params_level_strategy_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.4</span>
</div><p>Dynamically update the compression level and compression strategy.
Only applicable to deflate algorithm.</p>
<h3>zlib.reset()<span><a class="mark" href="#zlib_zlib_reset" id="zlib_zlib_reset">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.0</span>
</div><p>Reset the compressor/decompressor to factory defaults. Only applicable to
the inflate and deflate algorithms.</p>
<h2>zlib.createDeflate(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#zlib_zlib_createdeflate_options" id="zlib_zlib_createdeflate_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Returns a new <a href="#zlib_class_zlib_deflate">Deflate</a> object with an <a href="#zlib_class_options">options</a>.</p>
<h2>zlib.createDeflateRaw(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#zlib_zlib_createdeflateraw_options" id="zlib_zlib_createdeflateraw_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Returns a new <a href="#zlib_class_zlib_deflateraw">DeflateRaw</a> object with an <a href="#zlib_class_options">options</a>.</p>
<h2>zlib.createGunzip(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#zlib_zlib_creategunzip_options" id="zlib_zlib_creategunzip_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Returns a new <a href="#zlib_class_zlib_gunzip">Gunzip</a> object with an <a href="#zlib_class_options">options</a>.</p>
<h2>zlib.createGzip(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#zlib_zlib_creategzip_options" id="zlib_zlib_creategzip_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Returns a new <a href="#zlib_class_zlib_gzip">Gzip</a> object with an <a href="#zlib_class_options">options</a>.</p>
<h2>zlib.createInflate(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#zlib_zlib_createinflate_options" id="zlib_zlib_createinflate_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Returns a new <a href="#zlib_class_zlib_inflate">Inflate</a> object with an <a href="#zlib_class_options">options</a>.</p>
<h2>zlib.createInflateRaw(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#zlib_zlib_createinflateraw_options" id="zlib_zlib_createinflateraw_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Returns a new <a href="#zlib_class_zlib_inflateraw">InflateRaw</a> object with an <a href="#zlib_class_options">options</a>.</p>
<h2>zlib.createUnzip(<a href="#zlib_class_options">options</a>)<span><a class="mark" href="#zlib_zlib_createunzip_options" id="zlib_zlib_createunzip_options">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.8</span>
</div><p>Returns a new <a href="#zlib_class_zlib_unzip">Unzip</a> object with an <a href="#zlib_class_options">options</a>.</p>
<h2>Convenience Methods<span><a class="mark" href="#zlib_convenience_methods" id="zlib_convenience_methods">#</a></span></h2>
<!--type=misc-->
<p>All of these take a <a href="buffer.html">Buffer</a> or string as the first argument, an optional second
argument to supply options to the zlib classes and will call the supplied
callback with <code>callback(error, result)</code>.</p>
<p>Every method has a <code>*Sync</code> counterpart, which accept the same arguments, but
without a callback.</p>
<h3>zlib.deflate(buf[, options], callback)<span><a class="mark" href="#zlib_zlib_deflate_buf_options_callback" id="zlib_zlib_deflate_buf_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><h3>zlib.deflateSync(buf[, options])<span><a class="mark" href="#zlib_zlib_deflatesync_buf_options" id="zlib_zlib_deflatesync_buf_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>Compress a <a href="buffer.html">Buffer</a> or string with <a href="#zlib_class_zlib_deflate">Deflate</a>.</p>
<h3>zlib.deflateRaw(buf[, options], callback)<span><a class="mark" href="#zlib_zlib_deflateraw_buf_options_callback" id="zlib_zlib_deflateraw_buf_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><h3>zlib.deflateRawSync(buf[, options])<span><a class="mark" href="#zlib_zlib_deflaterawsync_buf_options" id="zlib_zlib_deflaterawsync_buf_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>Compress a <a href="buffer.html">Buffer</a> or string with <a href="#zlib_class_zlib_deflateraw">DeflateRaw</a>.</p>
<h3>zlib.gunzip(buf[, options], callback)<span><a class="mark" href="#zlib_zlib_gunzip_buf_options_callback" id="zlib_zlib_gunzip_buf_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><h3>zlib.gunzipSync(buf[, options])<span><a class="mark" href="#zlib_zlib_gunzipsync_buf_options" id="zlib_zlib_gunzipsync_buf_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>Decompress a <a href="buffer.html">Buffer</a> or string with <a href="#zlib_class_zlib_gunzip">Gunzip</a>.</p>
<h3>zlib.gzip(buf[, options], callback)<span><a class="mark" href="#zlib_zlib_gzip_buf_options_callback" id="zlib_zlib_gzip_buf_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><h3>zlib.gzipSync(buf[, options])<span><a class="mark" href="#zlib_zlib_gzipsync_buf_options" id="zlib_zlib_gzipsync_buf_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>Compress a <a href="buffer.html">Buffer</a> or string with <a href="#zlib_class_zlib_gzip">Gzip</a>.</p>
<h3>zlib.inflate(buf[, options], callback)<span><a class="mark" href="#zlib_zlib_inflate_buf_options_callback" id="zlib_zlib_inflate_buf_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><h3>zlib.inflateSync(buf[, options])<span><a class="mark" href="#zlib_zlib_inflatesync_buf_options" id="zlib_zlib_inflatesync_buf_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>Decompress a <a href="buffer.html">Buffer</a> or string with <a href="#zlib_class_zlib_inflate">Inflate</a>.</p>
<h3>zlib.inflateRaw(buf[, options], callback)<span><a class="mark" href="#zlib_zlib_inflateraw_buf_options_callback" id="zlib_zlib_inflateraw_buf_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><h3>zlib.inflateRawSync(buf[, options])<span><a class="mark" href="#zlib_zlib_inflaterawsync_buf_options" id="zlib_zlib_inflaterawsync_buf_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>Decompress a <a href="buffer.html">Buffer</a> or string with <a href="#zlib_class_zlib_inflateraw">InflateRaw</a>.</p>
<h3>zlib.unzip(buf[, options], callback)<span><a class="mark" href="#zlib_zlib_unzip_buf_options_callback" id="zlib_zlib_unzip_buf_options_callback">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span>
</div><h3>zlib.unzipSync(buf[, options])<span><a class="mark" href="#zlib_zlib_unzipsync_buf_options" id="zlib_zlib_unzipsync_buf_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.12</span>
</div><p>Decompress a <a href="buffer.html">Buffer</a> or string with <a href="#zlib_class_zlib_unzip">Unzip</a>.</p>
<!-- [end-include:zlib.md] -->
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