The Tor Browser / file revision

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 'use strict';

 module.metadata = {

   "stability": "unstable"

 };

 const { Cc, Ci } = require('chrome');

 const { Class } = require('../core/heritage');

 const { EventTarget } = require('../event/target');

 const { Branch } = require('./service');

 const { emit, off } = require('../event/core');

 const { when: unload } = require('../system/unload');

 const prefTargetNS = require('../core/namespace').ns();

 const PrefsTarget = Class({

   extends: EventTarget,

   initialize: function(options) {

     options = options || {};

     EventTarget.prototype.initialize.call(this, options);

     let branchName = options.branchName || '';

     let branch = Cc["@mozilla.org/preferences-service;1"].

         getService(Ci.nsIPrefService).

         getBranch(branchName).

         QueryInterface(Ci.nsIPrefBranch2);

     prefTargetNS(this).branch = branch;

     // provides easy access to preference values

     this.prefs = Branch(branchName);

     // start listening to preference changes

     let observer = prefTargetNS(this).observer = onChange.bind(this);

     branch.addObserver('', observer, false);

     // Make sure to destroy this on unload

     unload(destroy.bind(this));

   }

 });

 exports.PrefsTarget = PrefsTarget;

 /* HELPERS */

 function onChange(subject, topic, name) {

   if (topic === 'nsPref:changed') {

     emit(this, name, name);

     emit(this, '', name);

   }

 }

 function destroy() {

   off(this);

   // stop listening to preference changes

   let branch = prefTargetNS(this).branch;

   branch.removeObserver('', prefTargetNS(this).observer, false);

   prefTargetNS(this).observer = null;

 }