ajax局部刷新一个div下jsp内容的方法

<script type="text/javascript">
var xmlhttp;
function startrefresh(){
xmlhttp=new XMLHttpRequest();
xmlhttp.open("POST,"ss.jsp",true);
xmlhttp.setRequestHeader("Content-type","application/x--form-urlencoded");
//xmlhttp.send("name=wk"); --需要传输参数时增加
xmlhttp.onreadystatechange = function(){
if(xmlhttp.readyState == 4)
if(xmlhttp.status == 200)
document.getElementById("mydvi").innerHTML=xmlhttp.responseText;
}
}
</script>