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 /**
  11  * @typedef {EventListener|function(!Event):*}
  12  */
  13 var EventListenerType;
  14
  15 cr.define('cr', function() {
  16
  17   /**
  18    * Creates a new EventTarget. This class implements the DOM level 2
  19    * EventTarget interface and can be used wherever those are used.
  20    * @constructor
  21    * @implements {EventTarget}
  22    */
  23   function EventTarget() {
  24   }
  25
  26   EventTarget.prototype = {
  27     /**
  28      * Adds an event listener to the target.
  29      * @param {string} type The name of the event.
  30      * @param {EventListenerType} handler The handler for the event. This is
  31      *     called when the event is dispatched.
  32      */
  33     addEventListener: function(type, handler) {
  34       if (!this.listeners_)
  35         this.listeners_ = Object.create(null);
  36       if (!(type in this.listeners_)) {
  37         this.listeners_[type] = [handler];
  38       } else {
  39         var handlers = this.listeners_[type];
  40         if (handlers.indexOf(handler) < 0)
  41           handlers.push(handler);
  42       }
  43     },
  44
  45     /**
  46      * Removes an event listener from the target.
  47      * @param {string} type The name of the event.
  48      * @param {EventListenerType} handler The handler for the event.
  49      */
  50     removeEventListener: function(type, handler) {
  51       if (!this.listeners_)
  52         return;
  53       if (type in this.listeners_) {
  54         var handlers = this.listeners_[type];
  55         var index = handlers.indexOf(handler);
  56         if (index >= 0) {
  57           // Clean up if this was the last listener.
  58           if (handlers.length == 1)
  59             delete this.listeners_[type];
  60           else
  61             handlers.splice(index, 1);
  62         }
  63       }
  64     },
  65
  66     /**
  67      * Dispatches an event and calls all the listeners that are listening to
  68      * the type of the event.
  69      * @param {!Event} event The event to dispatch.
  70      * @return {boolean} Whether the default action was prevented. If someone
  71      *     calls preventDefault on the event object then this returns false.
  72      */
  73     dispatchEvent: function(event) {
  74       if (!this.listeners_)
  75         return true;
  76
  77       // Since we are using DOM Event objects we need to override some of the
  78       // properties and methods so that we can emulate this correctly.
  79       var self = this;
  80       event.__defineGetter__('target', function() {
  81         return self;
  82       });
  83
  84       var type = event.type;
  85       var prevented = 0;
  86       if (type in this.listeners_) {
  87         // Clone to prevent removal during dispatch
  88         var handlers = this.listeners_[type].concat();
  89         for (var i = 0, handler; handler = handlers[i]; i++) {
  90           if (handler.handleEvent)
  91             prevented |= handler.handleEvent.call(handler, event) === false;
  92           else
  93             prevented |= handler.call(this, event) === false;
  94         }
  95       }
  96
  97       return !prevented && !event.defaultPrevented;
  98     }
  99   };
 100
 101   // Export
 102   return {
 103     EventTarget: EventTarget
 104   };
 105 });