XHR对象

function createXHR(){
     if(typeof XMLHttpRequest != "undefined"){
        createXHR = function(){
            return new XMLHttpRequest();
        };
     }else if(typeof ActiveXObject != "undefined"){
         createXHR = function(){
            if(typeof arguments.callee.activeXString != "string"){
             var versions = ["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"];
             for(var i=0,len=versions.length;i<len;i++){
                 try{
                     var xhr = new ActiveXObject(versions[i]);
                     arguments.callee.activeXString = versions[i];
                     return xhr;
                 }catch (ex){
                     console.log("异常");
                 }
             }
         }
         return new ActiveXObject(arguments.callee.activeXString);
         };
     }else{
         createXHR = function(){
            throw new Error("No XHR object available.");
         };
     }
     return createXHR();
 }