src/third_party/closure_library/closure/goog/events/event.js

// 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 A base class for event objects.
 *
 */


goog.provide('goog.events.Event');
goog.provide('goog.events.EventLike');

/**
 * goog.events.Event no longer depends on goog.Disposable. Keep requiring
 * goog.Disposable here to not break projects which assume this dependency.
 * @suppress {extraRequire}
 */
goog.require('goog.Disposable');
goog.require('goog.events.EventId');


/**
 * A typedef for event like objects that are dispatchable via the
 * goog.events.dispatchEvent function. strings are treated as the type for a
 * goog.events.Event. Objects are treated as an extension of a new
 * goog.events.Event with the type property of the object being used as the type
 * of the Event.
 * @typedef {string|Object|goog.events.Event|goog.events.EventId}
 */
goog.events.EventLike;



/**
 * A base class for event objects, so that they can support preventDefault and
 * stopPropagation.
 *
 * @param {string|!goog.events.EventId} type Event Type.
 * @param {Object=} opt_target Reference to the object that is the target of
 *     this event. It has to implement the {@code EventTarget} interface
 *     declared at {@link http://developer.mozilla.org/en/DOM/EventTarget}.
 * @constructor
 */
goog.events.Event = function(type, opt_target) {
  /**
   * Event type.
   * @type {string}
   */
  this.type = type instanceof goog.events.EventId ? String(type) : type;

  /**
   * TODO(tbreisacher): The type should probably be
   * EventTarget|goog.events.EventTarget.
   *
   * Target of the event.
   * @type {Object|undefined}
   */
  this.target = opt_target;

  /**
   * Object that had the listener attached.
   * @type {Object|undefined}
   */
  this.currentTarget = this.target;

  /**
   * Whether to cancel the event in internal capture/bubble processing for IE.
   * @type {boolean}
   * @public
   * @suppress {underscore|visibility} Technically public, but referencing this
   *     outside this package is strongly discouraged.
   */
  this.propagationStopped_ = false;

  /**
   * Whether the default action has been prevented.
   * This is a property to match the W3C specification at
   * {@link http://www.w3.org/TR/DOM-Level-3-Events/
   * #events-event-type-defaultPrevented}.
   * Must be treated as read-only outside the class.
   * @type {boolean}
   */
  this.defaultPrevented = false;

  /**
   * Return value for in internal capture/bubble processing for IE.
   * @type {boolean}
   * @public
   * @suppress {underscore|visibility} Technically public, but referencing this
   *     outside this package is strongly discouraged.
   */
  this.returnValue_ = true;
};


/**
 * Stops event propagation.
 */
goog.events.Event.prototype.stopPropagation = function() {
  this.propagationStopped_ = true;
};


/**
 * Prevents the default action, for example a link redirecting to a url.
 */
goog.events.Event.prototype.preventDefault = function() {
  this.defaultPrevented = true;
  this.returnValue_ = false;
};


/**
 * Stops the propagation of the event. It is equivalent to
 * {@code e.stopPropagation()}, but can be used as the callback argument of
 * {@link goog.events.listen} without declaring another function.
 * @param {!goog.events.Event} e An event.
 */
goog.events.Event.stopPropagation = function(e) {
  e.stopPropagation();
};


/**
 * Prevents the default action. It is equivalent to
 * {@code e.preventDefault()}, but can be used as the callback argument of
 * {@link goog.events.listen} without declaring another function.
 * @param {!goog.events.Event} e An event.
 */
goog.events.Event.preventDefault = function(e) {
  e.preventDefault();
};