Issue 3862 - Add EventEmitter class and implement in the FilterNotifier

lib/events.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
@@ skipping 49 matching lines @@
   },
 
   /**
    * Adds a one time listener and returns a promise that
    * is resolved the next time the specified event is emitted.
    *
    * @return {Promise}
    */
   once: function(name)
   {
-    return new Promise(function(resolve)
+    return new Promise(resolve =>
     {
-      let listener = function()
+      let listener = () =>
       {
         this.off(name, listener);
         resolve();
-      }.bind(this);
+      };
 
       this.on(name, listener);
-    }.bind(this));
+    });
   },
 
   /**
    * Calls all previously added listeners for the given event name.
    *
    * @param {string} name
    * @param {...*}   [arg]
    */
   emit: function(name)
   {
     let listeners = this._listeners[name];
     if (listeners)
     {
       let args = [];
       for (let i = 1; i < arguments.length; i++)
         args.push(arguments[i]);
 
       let currentListeners = listeners.slice();
       for (let listener of currentListeners)
         listener.apply(null, args);
     }
   }
 };