js报错：Ajax 中onreadystatechange在ie7及以上浏览器兼容吗，为什么没有反应？求大神

function addLoadEvent(func){    //不管在页面加载完毕执行多少个函数，都应付自如
var oldonload = window.onload;
if(typeof window.onload != 'function'){
window.onload = func;
}else{
window.onload = function(){
oldonload();
func();
}
}
}

function getHTTPObject(){
if(typeof XMLHttpRequest == "undefined")
XMLHttpRequest = function(){
try {return new ActiveXObject("Msxml2.XMLHTTP.6.0");}
catch(e){}
try {return new ActiveXObject("Msxml2.XMLHTTP.3.0");}
catch(e){}
try{return new ActiveXObject("Msxml2.XMLHTTP");}
……