ui/webui/resources/js/cr/event_target.js

   1 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 /**
   6  * @fileoverview This contains an implementation of the EventTarget interface
   7  * as defined by DOM Level 2 Events.
   8  */
   9
  10 cr.define('cr', function() {
  11
  12   /**
  13    * Creates a new EventTarget. This class implements the DOM level 2
  14    * EventTarget interface and can be used wherever those are used.
  15    * @constructor
  16    */
  17   function EventTarget() {
  18   }
  19
  20   EventTarget.prototype = {
  21
  22     /**
  23      * Adds an event listener to the target.
  24      * @param {string} type The name of the event.
  25      * @param {!Function|{handleEvent:Function}} handler The handler for the
  26      *     event. This is called when the event is dispatched.
  27      */
  28     addEventListener: function(type, handler) {
  29       if (!this.listeners_)
  30         this.listeners_ = Object.create(null);
  31       if (!(type in this.listeners_)) {
  32         this.listeners_[type] = [handler];
  33       } else {
  34         var handlers = this.listeners_[type];
  35         if (handlers.indexOf(handler) < 0)
  36           handlers.push(handler);
  37       }
  38     },
  39
  40     /**
  41      * Removes an event listener from the target.
  42      * @param {string} type The name of the event.
  43      * @param {!Function|{handleEvent:Function}} handler The handler for the
  44      *     event.
  45      */
  46     removeEventListener: function(type, handler) {
  47       if (!this.listeners_)
  48         return;
  49       if (type in this.listeners_) {
  50         var handlers = this.listeners_[type];
  51         var index = handlers.indexOf(handler);
  52         if (index >= 0) {
  53           // Clean up if this was the last listener.
  54           if (handlers.length == 1)
  55             delete this.listeners_[type];
  56           else
  57             handlers.splice(index, 1);
  58         }
  59       }
  60     },
  61
  62     /**
  63      * Dispatches an event and calls all the listeners that are listening to
  64      * the type of the event.
  65      * @param {!cr.event.Event} event The event to dispatch.
  66      * @return {boolean} Whether the default action was prevented. If someone
  67      *     calls preventDefault on the event object then this returns false.
  68      */
  69     dispatchEvent: function(event) {
  70       if (!this.listeners_)
  71         return true;
  72
  73       // Since we are using DOM Event objects we need to override some of the
  74       // properties and methods so that we can emulate this correctly.
  75       var self = this;
  76       event.__defineGetter__('target', function() {
  77         return self;
  78       });
  79
  80       var type = event.type;
  81       var prevented = 0;
  82       if (type in this.listeners_) {
  83         // Clone to prevent removal during dispatch
  84         var handlers = this.listeners_[type].concat();
  85         for (var i = 0, handler; handler = handlers[i]; i++) {
  86           if (handler.handleEvent)
  87             prevented |= handler.handleEvent.call(handler, event) === false;
  88           else
  89             prevented |= handler.call(this, event) === false;
  90         }
  91       }
  92
  93       return !prevented && !event.defaultPrevented;
  94     }
  95   };
  96
  97   // Export
  98   return {
  99     EventTarget: EventTarget
 100   };
 101 });