/usr/share/cinnamon/js/misc/screenSaver.js is in cinnamon-common 2.8.6-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51  | // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
const Lang = imports.lang;
const Gio = imports.gi.Gio;
const ScreenSaverIface = 
    '<node> \
        <interface name="org.gnome.ScreenSaver"> \
        <method name="GetActive"> \
            <arg type="b" direction="out" /> \
        </method> \
        <method name="Lock" /> \
        <method name="SetActive"> \
            <arg type="b" direction="in" /> \
        </method> \
        <signal name="ActiveChanged"> \
            <arg type="b" direction="out" /> \
        </signal> \
        </interface> \
    </node>';
const ScreenSaverInfo = Gio.DBusInterfaceInfo.new_for_xml(ScreenSaverIface);
function ScreenSaverProxy() {
    var self = new Gio.DBusProxy({ g_connection: Gio.DBus.session,
                                   g_interface_name: ScreenSaverInfo.name,
                                   g_interface_info: ScreenSaverInfo,
                                   g_name: 'org.gnome.ScreenSaver',
                                   g_object_path: '/org/gnome/ScreenSaver',
                                   g_flags: (Gio.DBusProxyFlags.DO_NOT_AUTO_START |
                                             Gio.DBusProxyFlags.DO_NOT_LOAD_PROPERTIES) });
    self.init(null);
    self.screenSaverActive = false;
    self.connectSignal('ActiveChanged', function(proxy, senderName, [isActive]) {
        self.screenSaverActive = isActive;
    });
    self.connect('notify::g-name-owner', function() {
        if (self.g_name_owner) {
            self.GetActiveRemote(function(result, excp) {
                if (result) {
                    let [isActive] = result;
                    self.screenSaverActive = isActive;
                }
            });
        } else
            self.screenSaverActive = false;
    });
    return self;
}
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