xmlhttp 语法异常

            function CheckPoNoByRC(element)            {                var input = "<Root><Type>CurrencyPoNo</Type><Currency>" + element.value + "</Currency></Root>";                                //var xmlHttp  = new ActiveXObject("Microsoft.XMLHTTP");by brant                var xmlHttp;                    if(window.ActiveXObject)                    {                      xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");                    }                    else if(window.XMLHttpRequest)                    {                     xmlHttp=new XMLHttpRequest();                     }                xmlHttp.open("POST", "BQYFORM104CheckDataXMLHttpPost.aspx", false);                xmlHttp.onreadystatechange=callback;                xmlHttp.send(input);                //xmlHttp.onreadystatechange=callback();                //xmlHttp.send(input);//                var result = xmlHttp.responseText;//                alert(result);//                document.getElementById("lblPONumber").innerHTML = result;            }                        function callback()             {                if(xmlHttp.readyState==4)                 {                    var result=xmlHttp.responseText;                    document.getElementById("lblPONumber").innerHTML=result;                }             }