103 lines
3.1 KiB
JavaScript
103 lines
3.1 KiB
JavaScript
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// Copyright (c) 2010 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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/**
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* @fileoverview This contains an implementation of the EventTarget interface
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* as defined by DOM Level 2 Events.
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*/
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/**
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* @typedef {EventListener|function(!Event):*}
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*/
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var EventListenerType;
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cr.define('cr', function() {
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/**
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* Creates a new EventTarget. This class implements the DOM level 2
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* EventTarget interface and can be used wherever those are used.
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* @constructor
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* @implements {EventTarget}
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*/
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function EventTarget() {}
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EventTarget.prototype = {
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/**
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* Adds an event listener to the target.
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* @param {string} type The name of the event.
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* @param {EventListenerType} handler The handler for the event. This is
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* called when the event is dispatched.
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*/
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addEventListener: function(type, handler) {
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if (!this.listeners_)
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this.listeners_ = Object.create(null);
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if (!(type in this.listeners_)) {
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this.listeners_[type] = [handler];
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} else {
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var handlers = this.listeners_[type];
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if (handlers.indexOf(handler) < 0)
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handlers.push(handler);
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}
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},
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/**
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* Removes an event listener from the target.
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* @param {string} type The name of the event.
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* @param {EventListenerType} handler The handler for the event.
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*/
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removeEventListener: function(type, handler) {
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if (!this.listeners_)
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return;
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if (type in this.listeners_) {
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var handlers = this.listeners_[type];
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var index = handlers.indexOf(handler);
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if (index >= 0) {
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// Clean up if this was the last listener.
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if (handlers.length == 1)
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delete this.listeners_[type];
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else
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handlers.splice(index, 1);
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}
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}
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},
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/**
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* Dispatches an event and calls all the listeners that are listening to
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* the type of the event.
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* @param {!Event} event The event to dispatch.
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* @return {boolean} Whether the default action was prevented. If someone
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* calls preventDefault on the event object then this returns false.
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*/
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dispatchEvent: function(event) {
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if (!this.listeners_)
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return true;
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// Since we are using DOM Event objects we need to override some of the
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// properties and methods so that we can emulate this correctly.
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var self = this;
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event.__defineGetter__('target', function() {
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return self;
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});
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var type = event.type;
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var prevented = 0;
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if (type in this.listeners_) {
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// Clone to prevent removal during dispatch
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var handlers = this.listeners_[type].concat();
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for (var i = 0, handler; handler = handlers[i]; i++) {
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if (handler.handleEvent)
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prevented |= handler.handleEvent.call(handler, event) === false;
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else
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prevented |= handler.call(this, event) === false;
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}
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}
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return !prevented && !event.defaultPrevented;
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}
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};
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// Export
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return {EventTarget: EventTarget};
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});
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