text: // Copyright 2005 The Closure Library Authors. All Rights Reserved.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //      http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS-IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  /**
   * @fileoverview Implementation of EventTarget as defined by W3C DOM 2/3.
   *
   * @see ../demos/eventtarget.html
   */
  
  
  /**
   * Namespace for events
   */
  goog.provide('goog.events.EventTarget');
  
  goog.require('goog.Disposable');
  goog.require('goog.events');
  
  
  
  /**
   * Inherit from this class to give your object the ability to dispatch events.
   * Note that this class provides event <em>sending</em> behaviour, not event
   * receiving behaviour: your object will be able to broadcast events, and other
   * objects will be able to listen for those events using goog.events.listen().
   *
   * <p>The name "EventTarget" reflects the fact that this class implements the
   * <a href="http://www.w3.org/TR/DOM-Level-2-Events/events.html">
   * EventTarget interface</a> as defined by W3C DOM 2/3, with a few differences:
   * <ul>
   * <li>Event objects do not have to implement the Event interface. An object
   *     is treated as an event object if it has a 'type' property.
   * <li>You can use a plain string instead of an event object; an event-like
   *     object will be created with the 'type' set to the string value.
   * </ul>
   *
   * <p>Unless propagation is stopped, an event dispatched by an EventTarget
   * will bubble to the parent returned by <code>getParentEventTarget</code>.
   * To set the parent, call <code>setParentEventTarget</code> or override
   * <code>getParentEventTarget</code> in a subclass.  Subclasses that don't
   * support changing the parent should override the setter to throw an error.
   *
   * <p>Example usage:
   * <pre>
   *   var source = new goog.events.EventTarget();
   *   function handleEvent(event) {
   *     alert('Type: ' + e.type + '\nTarget: ' + e.target);
   *   }
   *   goog.events.listen(source, 'foo', handleEvent);
   *   ...
   *   source.dispatchEvent({type: 'foo'}); // will call handleEvent
   *   // or source.dispatchEvent('foo');
   *   ...
   *   goog.events.unlisten(source, 'foo', handleEvent);
   *
   *   // You can also use the Listener interface:
   *   var listener = {
   *     handleEvent: function(event) {
   *       ...
   *     }
   *   };
   *   goog.events.listen(source, 'bar', listener);
   * </pre>
   *
   * @constructor
   * @extends {goog.Disposable}
   */
  goog.events.EventTarget = function() {
    goog.Disposable.call(this);
  };
  goog.inherits(goog.events.EventTarget, goog.Disposable);
  
  
  /**
   * Used to tell if an event is a real event in goog.events.listen() so we don't
   * get listen() calling addEventListener() and vice-versa.
   * @type {boolean}
   * @private
   */
  goog.events.EventTarget.prototype.customEvent_ = true;
  
  
  /**
   * Parent event target, used during event bubbling.
   * @type {goog.events.EventTarget?}
   * @private
   */
  goog.events.EventTarget.prototype.parentEventTarget_ = null;
  
  
  /**
   * Returns the parent of this event target to use for bubbling.
   *
   * @return {goog.events.EventTarget} The parent EventTarget or null if there
   * is no parent.
   */
  goog.events.EventTarget.prototype.getParentEventTarget = function() {
    return this.parentEventTarget_;
  };
  
  
  /**
   * Sets the parent of this event target to use for bubbling.
   *
   * @param {goog.events.EventTarget?} parent Parent EventTarget (null if none).
   */
  goog.events.EventTarget.prototype.setParentEventTarget = function(parent) {
    this.parentEventTarget_ = parent;
  };
  
  
  /**
   * Adds an event listener to the event target. The same handler can only be
   * added once per the type. Even if you add the same handler multiple times
   * using the same type then it will only be called once when the event is
   * dispatched.
   *
   * Supported for legacy but use goog.events.listen(src, type, handler) instead.
   *
   * @param {string} type The type of the event to listen for.
   * @param {Function|Object} handler The function to handle the event. The
   *     handler can also be an object that implements the handleEvent method
   *     which takes the event object as argument.
   * @param {boolean=} opt_capture In DOM-compliant browsers, this determines
   *     whether the listener is fired during the capture or bubble phase
   *     of the event.
   * @param {Object=} opt_handlerScope Object in whose scope to call the listener.
   */
  goog.events.EventTarget.prototype.addEventListener = function(
      type, handler, opt_capture, opt_handlerScope) {
    goog.events.listen(this, type, handler, opt_capture, opt_handlerScope);
  };
  
  
  /**
   * Removes an event listener from the event target. The handler must be the
   * same object as the one added. If the handler has not been added then
   * nothing is done.
   * @param {string} type The type of the event to listen for.
   * @param {Function|Object} handler The function to handle the event. The
   *     handler can also be an object that implements the handleEvent method
   *     which takes the event object as argument.
   * @param {boolean=} opt_capture In DOM-compliant browsers, this determines
   *     whether the listener is fired during the capture or bubble phase
   *     of the event.
   * @param {Object=} opt_handlerScope Object in whose scope to call the listener.
   */
  goog.events.EventTarget.prototype.removeEventListener = function(
      type, handler, opt_capture, opt_handlerScope) {
    goog.events.unlisten(this, type, handler, opt_capture, opt_handlerScope);
  };
  
  
  /**
   * Dispatches an event (or event like object) and calls all listeners
   * listening for events of this type. The type of the event is decided by the
   * type property on the event object.
   *
   * If any of the listeners returns false OR calls preventDefault then this
   * function will return false.  If one of the capture listeners calls
   * stopPropagation, then the bubble listeners won't fire.
   *
   * @param {string|Object|goog.events.Event} e Event object.
   * @return {boolean} If anyone called preventDefault on the event object (or
   *     if any of the handlers returns false this will also return false.
   */
  goog.events.EventTarget.prototype.dispatchEvent = function(e) {
    return goog.events.dispatchEvent(this, e);
  };
  
  
  /**
   * Unattach listeners from this object.  Classes that extend EventTarget may
   * need to override this method in order to remove references to DOM Elements
   * and additional listeners, it should be something like this:
   * <pre>
   * MyClass.prototype.disposeInternal = function() {
   *   MyClass.superClass_.disposeInternal.call(this);
   *   // Dispose logic for MyClass
   * };
   * </pre>
   * @override
   * @protected
   */
  goog.events.EventTarget.prototype.disposeInternal = function() {
    goog.events.EventTarget.superClass_.disposeInternal.call(this);
    goog.events.removeAll(this);
    this.parentEventTarget_ = null;
  };
  