获取XmlHttpRequest对象

function ajaxFunction(){
   var xmlHttp;
   try{ // Firefox, Opera 8.0+, Safari
        xmlHttp=new XMLHttpRequest();
    }
    catch (e){
       try{// Internet Explorer
             xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
          }
        catch (e){
          try{
             xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
          }
          catch (e){}
          }
    }
    return xmlHttp;
 }

function getXMLHttpRequest(){
     var xmlHttpReq=null; 
     if (window.ActiveXObject) {//IE浏览器创建XMLHttpRequest对象
         xmlHttpReq = new ActiveXObject("MSXML2.XMLHTTP.3.0");
     }else if(window.XMLHttpRequest){
          xmlHttpReq = new XMLHttpRequest();
     }
     return xmlHttpReq;
}

function getXMLHttpRequest() {
    var xmlHttpReq=null;
    if (window.XMLHttpRequest) {//Mozilla 浏览器
        xmlHttpReq = new XMLHttpRequest();
    }else {
        if (window.ActiveXObject) {//IE 浏览器
            try {
                xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
            }
            catch (e) {
                try {//IE 浏览器
                    xmlHttpReq = new ActiveXObject("Msxml2.XMLHTTP");
                }
                catch (e) {
                }
            }
        }
    }
    return xmlHttpReq;
}