Issue 4795 - Use modern JavaScript syntax

lib/prefs.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 /** @module prefs */
 
-let {EventEmitter} = require("events");
+"use strict";
+
+const {EventEmitter} = require("events");
 
 const keyPrefix = "pref:";
 
 let eventEmitter = new EventEmitter();
 let overrides = Object.create(null);
 
 /** @lends module:prefs.Prefs */
 let defaults = Object.create(null);
 
 /**
@@ skipping 150 matching lines @@
   * @static
   */
 let Prefs = exports.Prefs = {
   /**
    * Adds a callback that is called when the
    * value of a specified preference changed.
    *
    * @param {string}   preference
    * @param {function} callback
    */
-  on: (preference, callback) =>
+  on(preference, callback)
   {
     eventEmitter.on(preference, callback);
   },
 
   /**
    * Removes a callback for the specified preference.
    *
    * @param {string}   preference
    * @param {function} callback
    */
-  off: (preference, callback) =>
+  off(preference, callback)
   {
     eventEmitter.off(preference, callback);
   },
 
   /**
    * A promise that is fullfilled when all preferences have been loaded.
    * Wait for this promise to be fulfilled before using preferences during
    * extension initialization.
    *
    * @type {Promise}
@@ skipping 10 matching lines @@
 }
 
 function prefToKey(pref)
 {
   return keyPrefix + pref;
 }
 
 function addPreference(pref)
 {
   Object.defineProperty(Prefs, pref, {
-    get: () => (pref in overrides ? overrides : defaults)[pref],
-    set: value =>
+    get() { return (pref in overrides ? overrides : defaults)[pref]; },
+    set(value)
     {
       let defaultValue = defaults[pref];
 
       if (typeof value != typeof defaultValue)
         throw new Error("Attempt to change preference type");
 
       if (value == defaultValue)
       {
         delete overrides[pref];
         ext.storage.remove(prefToKey(pref));
@@ skipping 64 matching lines @@
           eventEmitter.emit(pref);
         }
       }
     });
   }
 
   Prefs.untilLoaded = Promise.all([localLoaded, managedLoaded]).then(onLoaded);
 }
 
 init();