Ajax–readyState一直為0

readyState 一直為0表示對象已建立，串連未建立的狀態

我寫的代碼：

    function LoadXMLDoc(url,scope,orderID){        if(window.XMLHttpRequest){            xmlhttp = new XMLHttpRequest();        }else if(window.ActiveXObject){            xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");        }        alert(xmlhttp);        if(xmlhttp!=null){            xmlhttp.onreadystatechange = changeState();            xmlhttp.open("post",url,true);            xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");            xmlhttp.send("scope="+scope+"&orderID="+orderID);        }    }    function changeState(){        alert("q");        alert('state:'+xmlhttp.readyState);        alert('status:'+xmlhttp.status);        if(xmlhttp.readyState==4 && xmlhttp.status==200){            alert("Q");            window.location.reload();        }    }

後來終於解決了，是因為這句：xmlhttp.onreadystatechange = changeState();這樣寫的話xmlhttp.onreadystatechange為將changeState的傳回值賦給xmlhttp.onreadystatechange；而xmlhttp.onreadystatechange為當狀態改變時調用函數changeState，所以應該這樣寫：xmlhttp.onreadystatechange=changgeState，如果有參數的話這樣寫：xmlhttp.onreadystatechange = functiong (){changeState(a,b);};