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 62 matching lines @@
       {
         this.off(name, listener);
         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)
+  {
+    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 listeners = this._listeners[name];
-    if (listeners)
-    {
-      let args = [];
-      for (let i = 1; i < arguments.length; i++)
-        args.push(arguments[i]);
+    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 currentListeners = listeners.slice();
-      for (let listener of currentListeners)
-        listener.apply(null, args);
-    }
+    let listeners = this.listeners(name);
+    for (let listener of listeners)
+      listener.apply(null, args);
   }
 };