Issue 3826 - Filter preference change events

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
  * 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 events */
 
 "use strict";
 
 /**
  * Registers and emits names events.
  *
  * @constructor
  */
 exports.EventEmitter = function()
 {
-  this._callbacks = Object.create(null);
+  this._listeners = Object.create(null);
 };
 
 exports.EventEmitter.prototype = {
   /**
-   * Adds a callback for the specified event name.
+   * Adds a listener for the specified event name.
    *
    * @param {string}   name
-   * @param {function} callback
+   * @param {function} listener
    */
-  on: function(name, callback)
+  on: function(name, listener)
   {
-    if (name in this._callbacks)
-      this._callbacks[name].push(callback);
+    if (name in this._listeners)
+      this._listeners[name].push(listener);
     else
-      this._callbacks[name] = [callback];
+      this._listeners[name] = [listener];
   },
 
   /**
-   * Removes a callback for the specified event name.
+   * Removes a listener for the specified event name.
    *
    * @param {string}   name
-   * @param {function} callback
+   * @param {function} listener
    */
-  off: function(name, callback)
+  off: function(name, listener)
   {
-    let callbacks = this._callbacks[name];
-    if (callbacks)
+    let listeners = this._listeners[name];
+    if (listeners)
     {
-      let idx = callbacks.indexOf(callback);
+      let idx = listeners.indexOf(listener);
       if (idx != -1)
-        callbacks.splice(idx, 1);
+        listeners.splice(idx, 1);
     }
   },
 
   /**
-   * Calls all previously added callbacks for the given event name.
+   * Calls all previously added listeners for the given event name.
    *
    * @param {string} name
    * @param {...*}   [arg]
    */
   emit: function(name)
   {
-    let callbacks = this._callbacks[name];
-    if (callbacks)
+    let listeners = this._listeners[name];
+    if (listeners)
     {
-      for (let callback of callbacks)
-        callbacks.apply(null, Array.prototype.slice.call(arguments, 1));
+      let args = [];

[Sebastian Noack, 2016/03/23 11:37:22]

Array.prototype.slice.call(arguments, 1), or passing arguments as array-like
object to another function, causes this function to be deoptimized in V8. So I
replaced it with a loop.

[kzar, 2016/03/23 11:56:01]

Acknowledged.

+      for (let i = 1; i < arguments.length; i++)
+        args.push(arguments[i]);
+
+      let currentListeners = listeners.slice();

[Sebastian Noack, 2016/03/23 11:37:22]

This is necessary to avoid side effects when a listener added/removed listeners
itself.

[kzar, 2016/03/23 11:56:01]

Acknowledged.

+      for (let listener of currentListeners)
+        listener.apply(null, args);
     }
   }
 };

[Sebastian Noack, 2016/03/23 11:37:22]

Moreover, I think "listener" is a more appropriate name than "callback" in the
context here. So I changed that as well.