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1 // Copyright (c) 2012 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 base.exportTo('ui', function() { | |
10 | |
11 /** | |
12 * Creates a new EventTarget. This class implements the DOM level 2 | |
13 * EventTarget interface and can be used wherever those are used. | |
14 * @constructor | |
15 */ | |
16 function EventTarget() { | |
17 } | |
18 | |
19 EventTarget.prototype = { | |
20 | |
21 /** | |
22 * Adds an event listener to the target. | |
23 * @param {string} type The name of the event. | |
24 * @param {!Function|{handleEvent:Function}} handler The handler for the | |
25 * event. This is called when the event is dispatched. | |
26 */ | |
27 addEventListener: function(type, handler) { | |
28 if (!this.listeners_) | |
29 this.listeners_ = Object.create(null); | |
30 if (!(type in this.listeners_)) { | |
31 this.listeners_[type] = [handler]; | |
32 } else { | |
33 var handlers = this.listeners_[type]; | |
34 if (handlers.indexOf(handler) < 0) | |
35 handlers.push(handler); | |
36 } | |
37 }, | |
38 | |
39 /** | |
40 * Removes an event listener from the target. | |
41 * @param {string} type The name of the event. | |
42 * @param {!Function|{handleEvent:Function}} handler The handler for the | |
43 * event. | |
44 */ | |
45 removeEventListener: function(type, handler) { | |
46 if (!this.listeners_) | |
47 return; | |
48 if (type in this.listeners_) { | |
49 var handlers = this.listeners_[type]; | |
50 var index = handlers.indexOf(handler); | |
51 if (index >= 0) { | |
52 // Clean up if this was the last listener. | |
53 if (handlers.length == 1) | |
54 delete this.listeners_[type]; | |
55 else | |
56 handlers.splice(index, 1); | |
57 } | |
58 } | |
59 }, | |
60 | |
61 /** | |
62 * Dispatches an event and calls all the listeners that are listening to | |
63 * the type of the event. | |
64 * @param {!cr.event.Event} event The event to dispatch. | |
65 * @return {boolean} Whether the default action was prevented. If someone | |
66 * calls preventDefault on the event object then this returns false. | |
67 */ | |
68 dispatchEvent: function(event) { | |
69 if (!this.listeners_) | |
70 return true; | |
71 | |
72 // Since we are using DOM Event objects we need to override some of the | |
73 // properties and methods so that we can emulate this correctly. | |
74 var self = this; | |
75 event.__defineGetter__('target', function() { | |
76 return self; | |
77 }); | |
78 event.preventDefault = function() { | |
79 this.returnValue = false; | |
80 }; | |
81 | |
82 var type = event.type; | |
83 var prevented = 0; | |
84 if (type in this.listeners_) { | |
85 // Clone to prevent removal during dispatch | |
86 var handlers = this.listeners_[type].concat(); | |
87 for (var i = 0, handler; handler = handlers[i]; i++) { | |
88 if (handler.handleEvent) | |
89 prevented |= handler.handleEvent.call(handler, event) === false; | |
90 else | |
91 prevented |= handler.call(this, event) === false; | |
92 } | |
93 } | |
94 | |
95 return !prevented && event.returnValue; | |
96 } | |
97 }; | |
98 | |
99 // Export | |
100 return { | |
101 EventTarget: EventTarget | |
102 }; | |
103 }); | |
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