EventDispatcher.js

/*
* EventDispatcher
* Visit http://createjs.com/ for documentation, updates and examples.
*
* Copyright (c) 2010 gskinner.com, inc.
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/

/**
 * @module CreateJS
 */

// namespace:
this.createjs = this.createjs||{};

(function() {
	"use strict";


// constructor:
	/**
	 * EventDispatcher provides methods for managing queues of event listeners and dispatching events.
	 *
	 * You can either extend EventDispatcher or mix its methods into an existing prototype or instance by using the
	 * EventDispatcher {{#crossLink "EventDispatcher/initialize"}}{{/crossLink}} method.
	 * 
	 * Together with the CreateJS Event class, EventDispatcher provides an extended event model that is based on the
	 * DOM Level 2 event model, including addEventListener, removeEventListener, and dispatchEvent. It supports
	 * bubbling / capture, preventDefault, stopPropagation, stopImmediatePropagation, and handleEvent.
	 * 
	 * EventDispatcher also exposes a {{#crossLink "EventDispatcher/on"}}{{/crossLink}} method, which makes it easier
	 * to create scoped listeners, listeners that only run once, and listeners with associated arbitrary data. The 
	 * {{#crossLink "EventDispatcher/off"}}{{/crossLink}} method is merely an alias to
	 * {{#crossLink "EventDispatcher/removeEventListener"}}{{/crossLink}}.
	 * 
	 * Another addition to the DOM Level 2 model is the {{#crossLink "EventDispatcher/removeAllEventListeners"}}{{/crossLink}}
	 * method, which can be used to listeners for all events, or listeners for a specific event. The Event object also 
	 * includes a {{#crossLink "Event/remove"}}{{/crossLink}} method which removes the active listener.
	 *
	 * <h4>Example</h4>
	 * Add EventDispatcher capabilities to the "MyClass" class.
	 *
	 *      EventDispatcher.initialize(MyClass.prototype);
	 *
	 * Add an event (see {{#crossLink "EventDispatcher/addEventListener"}}{{/crossLink}}).
	 *
	 *      instance.addEventListener("eventName", handlerMethod);
	 *      function handlerMethod(event) {
	 *          console.log(event.target + " Was Clicked");
	 *      }
	 *
	 * <b>Maintaining proper scope</b><br />
	 * Scope (ie. "this") can be be a challenge with events. Using the {{#crossLink "EventDispatcher/on"}}{{/crossLink}}
	 * method to subscribe to events simplifies this.
	 *
	 *      instance.addEventListener("click", function(event) {
	 *          console.log(instance == this); // false, scope is ambiguous.
	 *      });
	 *      
	 *      instance.on("click", function(event) {
	 *          console.log(instance == this); // true, "on" uses dispatcher scope by default.
	 *      });
	 * 
	 * If you want to use addEventListener instead, you may want to use function.bind() or a similar proxy to manage
	 * scope.
	 *
	 * <b>Browser support</b>
	 * The event model in CreateJS can be used separately from the suite in any project, however the inheritance model
	 * requires modern browsers (IE9+).
	 *      
	 *
	 * @class EventDispatcher
	 * @constructor
	 **/
	function EventDispatcher() {
	
	
	// private properties:
		/**
		 * @protected
		 * @property _listeners
		 * @type Object
		 **/
		this._listeners = null;
		
		/**
		 * @protected
		 * @property _captureListeners
		 * @type Object
		 **/
		this._captureListeners = null;
	}
	var p = EventDispatcher.prototype;

// static public methods:
	/**
	 * Static initializer to mix EventDispatcher methods into a target object or prototype.
	 * 
	 * 		EventDispatcher.initialize(MyClass.prototype); // add to the prototype of the class
	 * 		EventDispatcher.initialize(myObject); // add to a specific instance
	 * 
	 * @method initialize
	 * @static
	 * @param {Object} target The target object to inject EventDispatcher methods into. This can be an instance or a
	 * prototype.
	 **/
	EventDispatcher.initialize = function(target) {
		target.addEventListener = p.addEventListener;
		target.on = p.on;
		target.removeEventListener = target.off =  p.removeEventListener;
		target.removeAllEventListeners = p.removeAllEventListeners;
		target.hasEventListener = p.hasEventListener;
		target.dispatchEvent = p.dispatchEvent;
		target._dispatchEvent = p._dispatchEvent;
		target.willTrigger = p.willTrigger;
	};
	

// public methods:
	/**
	 * Adds the specified event listener. Note that adding multiple listeners to the same function will result in
	 * multiple callbacks getting fired.
	 *
	 * <h4>Example</h4>
	 *
	 *      displayObject.addEventListener("click", handleClick);
	 *      function handleClick(event) {
	 *         // Click happened.
	 *      }
	 *
	 * @method addEventListener
	 * @param {String} type The string type of the event.
	 * @param {Function | Object} listener An object with a handleEvent method, or a function that will be called when
	 * the event is dispatched.
	 * @param {Boolean} [useCapture] For events that bubble, indicates whether to listen for the event in the capture or bubbling/target phase.
	 * @return {Function | Object} Returns the listener for chaining or assignment.
	 **/
	p.addEventListener = function(type, listener, useCapture) {
		var listeners;
		if (useCapture) {
			listeners = this._captureListeners = this._captureListeners||{};
		} else {
			listeners = this._listeners = this._listeners||{};
		}
		var arr = listeners[type];
		if (arr) { this.removeEventListener(type, listener, useCapture); }
		arr = listeners[type]; // remove may have deleted the array
		if (!arr) { listeners[type] = [listener];  }
		else { arr.push(listener); }
		return listener;
	};
	
	/**
	 * A shortcut method for using addEventListener that makes it easier to specify an execution scope, have a listener
	 * only run once, associate arbitrary data with the listener, and remove the listener.
	 * 
	 * This method works by creating an anonymous wrapper function and subscribing it with addEventListener.
	 * The wrapper function is returned for use with `removeEventListener` (or `off`).
	 * 
	 * <b>IMPORTANT:</b> To remove a listener added with `on`, you must pass in the returned wrapper function as the listener, or use
	 * {{#crossLink "Event/remove"}}{{/crossLink}}. Likewise, each time you call `on` a NEW wrapper function is subscribed, so multiple calls
	 * to `on` with the same params will create multiple listeners.
	 * 
	 * <h4>Example</h4>
	 * 
	 * 		var listener = myBtn.on("click", handleClick, null, false, {count:3});
	 * 		function handleClick(evt, data) {
	 * 			data.count -= 1;
	 * 			console.log(this == myBtn); // true - scope defaults to the dispatcher
	 * 			if (data.count == 0) {
	 * 				alert("clicked 3 times!");
	 * 				myBtn.off("click", listener);
	 * 				// alternately: evt.remove();
	 * 			}
	 * 		}
	 * 
	 * @method on
	 * @param {String} type The string type of the event.
	 * @param {Function | Object} listener An object with a handleEvent method, or a function that will be called when
	 * the event is dispatched.
	 * @param {Object} [scope] The scope to execute the listener in. Defaults to the dispatcher/currentTarget for function listeners, and to the listener itself for object listeners (ie. using handleEvent).
	 * @param {Boolean} [once=false] If true, the listener will remove itself after the first time it is triggered.
	 * @param {*} [data] Arbitrary data that will be included as the second parameter when the listener is called.
	 * @param {Boolean} [useCapture=false] For events that bubble, indicates whether to listen for the event in the capture or bubbling/target phase.
	 * @return {Function} Returns the anonymous function that was created and assigned as the listener. This is needed to remove the listener later using .removeEventListener.
	 **/
	p.on = function(type, listener, scope, once, data, useCapture) {
		if (listener.handleEvent) {
			scope = scope||listener;
			listener = listener.handleEvent;
		}
		scope = scope||this;
		return this.addEventListener(type, function(evt) {
				listener.call(scope, evt, data);
				once&&evt.remove();
			}, useCapture);
	};

	/**
	 * Removes the specified event listener.
	 *
	 * <b>Important Note:</b> that you must pass the exact function reference used when the event was added. If a proxy
	 * function, or function closure is used as the callback, the proxy/closure reference must be used - a new proxy or
	 * closure will not work.
	 *
	 * <h4>Example</h4>
	 *
	 *      displayObject.removeEventListener("click", handleClick);
	 *
	 * @method removeEventListener
	 * @param {String} type The string type of the event.
	 * @param {Function | Object} listener The listener function or object.
	 * @param {Boolean} [useCapture] For events that bubble, indicates whether to listen for the event in the capture or bubbling/target phase.
	 **/
	p.removeEventListener = function(type, listener, useCapture) {
		var listeners = useCapture ? this._captureListeners : this._listeners;
		if (!listeners) { return; }
		var arr = listeners[type];
		if (!arr) { return; }
		for (var i=0,l=arr.length; i<l; i++) {
			if (arr[i] == listener) {
				if (l==1) { delete(listeners[type]); } // allows for faster checks.
				else { arr.splice(i,1); }
				break;
			}
		}
	};
	
	/**
	 * A shortcut to the removeEventListener method, with the same parameters and return value. This is a companion to the
	 * .on method.
	 * 
	 * <b>IMPORTANT:</b> To remove a listener added with `on`, you must pass in the returned wrapper function as the listener. See 
	 * {{#crossLink "EventDispatcher/on"}}{{/crossLink}} for an example.
	 *
	 * @method off
	 * @param {String} type The string type of the event.
	 * @param {Function | Object} listener The listener function or object.
	 * @param {Boolean} [useCapture] For events that bubble, indicates whether to listen for the event in the capture or bubbling/target phase.
	 **/
	p.off = p.removeEventListener;

	/**
	 * Removes all listeners for the specified type, or all listeners of all types.
	 *
	 * <h4>Example</h4>
	 *
	 *      // Remove all listeners
	 *      displayObject.removeAllEventListeners();
	 *
	 *      // Remove all click listeners
	 *      displayObject.removeAllEventListeners("click");
	 *
	 * @method removeAllEventListeners
	 * @param {String} [type] The string type of the event. If omitted, all listeners for all types will be removed.
	 **/
	p.removeAllEventListeners = function(type) {
		if (!type) { this._listeners = this._captureListeners = null; }
		else {
			if (this._listeners) { delete(this._listeners[type]); }
			if (this._captureListeners) { delete(this._captureListeners[type]); }
		}
	};

	/**
	 * Dispatches the specified event to all listeners.
	 *
	 * <h4>Example</h4>
	 *
	 *      // Use a string event
	 *      this.dispatchEvent("complete");
	 *
	 *      // Use an Event instance
	 *      var event = new createjs.Event("progress");
	 *      this.dispatchEvent(event);
	 *
	 * @method dispatchEvent
	 * @param {Object | String | Event} eventObj An object with a "type" property, or a string type.
	 * While a generic object will work, it is recommended to use a CreateJS Event instance. If a string is used,
	 * dispatchEvent will construct an Event instance if necessary with the specified type. This latter approach can
	 * be used to avoid event object instantiation for non-bubbling events that may not have any listeners.
	 * @param {Boolean} [bubbles] Specifies the `bubbles` value when a string was passed to eventObj.
	 * @param {Boolean} [cancelable] Specifies the `cancelable` value when a string was passed to eventObj.
	 * @return {Boolean} Returns false if `preventDefault()` was called on a cancelable event, true otherwise.
	 **/
	p.dispatchEvent = function(eventObj, bubbles, cancelable) {
		if (typeof eventObj == "string") {
			// skip everything if there's no listeners and it doesn't bubble:
			var listeners = this._listeners;
			if (!bubbles && (!listeners || !listeners[eventObj])) { return true; }
			eventObj = new createjs.Event(eventObj, bubbles, cancelable);
		} else if (eventObj.target && eventObj.clone) {
			// redispatching an active event object, so clone it:
			eventObj = eventObj.clone();
		}
		
		// TODO: it would be nice to eliminate this. Maybe in favour of evtObj instanceof Event? Or !!evtObj.createEvent
		try { eventObj.target = this; } catch (e) {} // try/catch allows redispatching of native events

		if (!eventObj.bubbles || !this.parent) {
			this._dispatchEvent(eventObj, 2);
		} else {
			var top=this, list=[top];
			while (top.parent) { list.push(top = top.parent); }
			var i, l=list.length;

			// capture & atTarget
			for (i=l-1; i>=0 && !eventObj.propagationStopped; i--) {
				list[i]._dispatchEvent(eventObj, 1+(i==0));
			}
			// bubbling
			for (i=1; i<l && !eventObj.propagationStopped; i++) {
				list[i]._dispatchEvent(eventObj, 3);
			}
		}
		return !eventObj.defaultPrevented;
	};

	/**
	 * Indicates whether there is at least one listener for the specified event type.
	 * @method hasEventListener
	 * @param {String} type The string type of the event.
	 * @return {Boolean} Returns true if there is at least one listener for the specified event.
	 **/
	p.hasEventListener = function(type) {
		var listeners = this._listeners, captureListeners = this._captureListeners;
		return !!((listeners && listeners[type]) || (captureListeners && captureListeners[type]));
	};
	
	/**
	 * Indicates whether there is at least one listener for the specified event type on this object or any of its
	 * ancestors (parent, parent's parent, etc). A return value of true indicates that if a bubbling event of the
	 * specified type is dispatched from this object, it will trigger at least one listener.
	 * 
	 * This is similar to {{#crossLink "EventDispatcher/hasEventListener"}}{{/crossLink}}, but it searches the entire
	 * event flow for a listener, not just this object.
	 * @method willTrigger
	 * @param {String} type The string type of the event.
	 * @return {Boolean} Returns `true` if there is at least one listener for the specified event.
	 **/
	p.willTrigger = function(type) {
		var o = this;
		while (o) {
			if (o.hasEventListener(type)) { return true; }
			o = o.parent;
		}
		return false;
	};

	/**
	 * @method toString
	 * @return {String} a string representation of the instance.
	 **/
	p.toString = function() {
		return "[EventDispatcher]";
	};


// private methods:
	/**
	 * @method _dispatchEvent
	 * @param {Object | Event} eventObj
	 * @param {Object} eventPhase
	 * @protected
	 **/
	p._dispatchEvent = function(eventObj, eventPhase) {
		var l, arr, listeners = (eventPhase <= 2) ? this._captureListeners : this._listeners;
		if (eventObj && listeners && (arr = listeners[eventObj.type]) && (l=arr.length)) {
			try { eventObj.currentTarget = this; } catch (e) {}
			try { eventObj.eventPhase = eventPhase|0; } catch (e) {}
			eventObj.removed = false;
			
			arr = arr.slice(); // to avoid issues with items being removed or added during the dispatch
			for (var i=0; i<l && !eventObj.immediatePropagationStopped; i++) {
				var o = arr[i];
				if (o.handleEvent) { o.handleEvent(eventObj); }
				else { o(eventObj); }
				if (eventObj.removed) {
					this.off(eventObj.type, o, eventPhase==1);
					eventObj.removed = false;
				}
			}
		}
		if (eventPhase === 2) { this._dispatchEvent(eventObj, 2.1); }
	};


	createjs.EventDispatcher = EventDispatcher;
}());