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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
10cr.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 {!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});
102