javascript: Xhr with queue example

RequesQ.js

/* Queue to use in conjuction with xhr functionality */
var requestQ = (function() {
	var numRequestToComplete, requestsCompleted, callBacks, singleCallBack;
	return function(options) {
		if (!options) options = {};
		numRequestToComplete = options.numRequest || 0;
		requestsCompleted = options.requestsCompleted || 0;
		callBacks = [];
		var fireCallbacks = function() {
			/* alert("we're all complete"); */
			for (var i = 0; i < callBacks.length; i++) callBacks[i]();
		};
		if (options.singleCallback) callBacks.push(options.singleCallback);
		this.addCallbackToQueue = function(isComplete, callback) {
			if (isComplete) requestsCompleted++;
			if (callback) callBacks.push(callback);
			if (requestsCompleted == numRequestToComplete) fireCallbacks();
		};
		this.requestComplete = function(isComplete) {
			if (isComplete) requestsCompleted++;
			if (requestsCompleted == numRequestToComplete) fireCallbacks();
		};
		this.setCallback = function(callback) {
			callBacks.push(callBack);
		};
	};
})();

Xhr

/* XHR */
(function(win, doc){
	//http://code.google.com/p/browsersec/wiki/Part2#Same-origin_policy_for_XMLHttpRequest
	"use strict";	
	var xhr = {
		_XMLHttpFactories: [
			function () {return new XMLHttpRequest()},
			function () {return new ActiveXObject("Msxml2.XMLHTTP")},
			function () {return new ActiveXObject("Msxml3.XMLHTTP")},
			function () {return new ActiveXObject("Microsoft.XMLHTTP")}
		],
		_createXMLHTTPObject: function(){
			var xmlhttp = false;
			for (var i=0;i< xhr._XMLHttpFactories.length;i++) {
				try {	xmlhttp = xhr._XMLHttpFactories[i](); }
				catch (e) { continue;}
				break;
			}
			return xmlhttp;
		},
		sendRequest: function(url, cb, data) {
            var req = xhr._createXMLHTTPObject();
            if (!req) return;
            var method = (data) ? "POST" : "GET";
            req.open(method, url, true);
            //req.setRequestHeader('User-Agent', 'XMLHTTP/1.0');
            if (data) req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
            req.onreadystatechange = function() {
                if (req.readyState != 4) return;
                if (req.status != 200 && req.status != 304) {
                    //alert('HTTP error ' + req.status);
                    return;
                }
                cb(req);
            }
            if (req.readyState == 4) return;
            req.send(data);
        }
	};
        // example
	xhr.sendRequest(window.location.href, function( req ){
		console.log(req);
	}, 'a=2&b=3&c=4');
	
})(window, document);