var XMLHttp = {
    _objPool: [],
    _getInstance: function (){
        for (var i = 0; i < this._objPool.length; i ++){
            if (this._objPool[i].readyState == 0 || this._objPool[i].readyState == 4){
                return this._objPool[i];
            }
        }
        this._objPool[this._objPool.length] = this._createObj();
        return this._objPool[this._objPool.length - 1];
    },
	 _createObj: function (){
        if (window.XMLHttpRequest){
            var objXMLHttp = new XMLHttpRequest();
        }
        else{
            var MSXML = ['MSXML2.XMLHTTP.5.0', 'MSXML2.XMLHTTP.4.0', 'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP', 'Microsoft.XMLHTTP'];
            for(var n = 0; n < MSXML.length; n ++){
                try{
                    var objXMLHttp = new ActiveXObject(MSXML[n]);
                    break;
                }
                catch(e){
                	alert(e.message);
                }
            }
         }
        if (objXMLHttp.readyState == null){
            objXMLHttp.readyState = 0;
            objXMLHttp.addEventListener("load", function (){
                    objXMLHttp.readyState = 4;
                    if (typeof objXMLHttp.onreadystatechange == "function"){
                        objXMLHttp.onreadystatechange();
                    }
                },  false);
        }
        return objXMLHttp;
    },
    sendReq: function (method, url, data, callback,requesttype){
        var objXMLHttp = this._getInstance();
        with(objXMLHttp){
            try{
                if (url.indexOf("?") > 0){
                    url += "&randnum=" + Math.random();
                }
                else{
                    url += "?randnum=" + Math.random();
                }
                open(method, url, true);
                setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
                send(data);
                onreadystatechange = function (){
                    if (objXMLHttp.readyState == 4 && (objXMLHttp.status == 200 || objXMLHttp.status == 304))
                    {
                        callback(objXMLHttp,requesttype);
                    }
                }
            }
            catch(e){
                alert(e.message);
            }
        }
    }
};