Issue 3862 - Added EventEmitter.listeners()

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 64 matching lines @@
         resolve();
       };
 
       this.on(name, listener);
     });
   },
 
   /**
    * Returns a copy of the array of listeners for the specified event.
    *
+   * @param {string} name
    * @return {function[]}
    */
   listeners: function(name)

[Sebastian Noack, 2016/03/24 11:07:13]

node.js has that method as well. We need it to reuse EventEmitter to implement
messaging.Port. Currently, in adblockpluschrome we access the private property
_listeners directly which isn't great and requires some duplication, in
particular if we want to slice the array to allow adding/removing listeners from
a listener function.

   {
     let listeners = this._listeners[name];
     return listeners ? listeners.slice() : [];
   },
 
   /**
    * Calls all previously added listeners for the given event name.
    *
    * @param {string} name
    * @param {...*}   [arg]
    */
   emit: function(name)
   {
     let args = [];

[kzar, 2016/03/24 11:29:53]

Any reason why you now create the args array even when there are no listeners?

[Sebastian Noack, 2016/03/24 11:33:27]

To keep the logic simple. Before we had to handle the case of this._listeners
being undefined anyway, otherwise slicing or iterating over it would fail
anyway. So I created the args array in the same code path. This check however
isn't necessary anymore, and checking for listeners.length instead would be
redundant, but just a micro-optimization.

[kzar, 2016/03/24 11:35:58]

Fair enough I guess

     for (let i = 1; i < arguments.length; i++)
       args.push(arguments[i]);
 
     let listeners = this.listeners(name);
     for (let listener of listeners)
       listener.apply(null, args);
   }
 };