Twisted style Deferred in Javascript

deferred.js

/*
 * Copyright (c) 2012, Jonas Obrist
 *	All rights reserved.
 *	
 *	Redistribution and use in source and binary forms, with or without
 *	modification, are permitted provided that the following conditions are met:
 *	    * Redistributions of source code must retain the above copyright
 *	      notice, this list of conditions and the following disclaimer.
 *	    * Redistributions in binary form must reproduce the above copyright
 *	      notice, this list of conditions and the following disclaimer in the
 *	      documentation and/or other materials provided with the distribution.
 *	    * Neither the name of Jonas Obrist nor the
 *	      names of its contributors may be used to endorse or promote products
 *	      derived from this software without specific prior written permission.
 *	
 *	THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 *	ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 *	WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 *	DISCLAIMED. IN NO EVENT SHALL JONAS OBRIST BE LIABLE FOR ANY
 *	DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 *	(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 *	LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 *	ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *	(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 *	SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
function Deferred(){
	/*
	 * Twisted styled deferred.
	 * Has addCallback and addErrback functions to add listeners for success
	 * and error callbacks.
	 * 
	 * Calling callback or errback triggers the stored listeners. Any call to
	 * addCallback/addErrback after that point just calls the listener
	 * immediately.
	 */
	var internal = {
		state: 'new',
		callbacks: [],
		errbacks: []
	};
	
	function iter(arr){
		// Internal function to iterate over an array of callbacks and calling
		// it with the stored arguments
		var len = arr.length;
		for (var index = 0; index < len; index++){
			arr[index].apply(null, internal.arguments);
		}
	}
	
	this.addCallback = function(callback){
		if (internal.state != 'called'){
			internal.callbacks.push(callback);
		} else {
			callback.apply(null, internal.arguments);
		}
		return this;
	};

	this.addErrback = function(errback){
		if (internal.state != 'failed'){
			internal.errbacks.push(errback);
		} else {
			errback.apply(null, internal.arguments);
		}
		return this;
	};

	this.callback = function(){
		if (internal.state != 'new'){
			throw "Can only fire a Deferred once";
		}
		internal.state = 'called';
		internal.arguments = arguments;
		iter(internal.callbacks);
	};

	this.errback = function(){
		if (internal.state != 'new'){
			throw "Can only fire a Deferred once";
		}
		internal.state = 'failed';
		internal.arguments = arguments;
		iter(internal.errbacks);
	};
}