ajax典型用法举例

<script language="javascript">
var xmlHttp=false ;

function createXMLHttpRequest() {
	if(window.ActiveXObject){
		xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
	}else if(window.XMLHttpRequest){
		xmlHttp = new XMLHttpRequest();
	}
}
function startRequest(){
	createXMLHttpRequest();
	var username = document.form.user_name.value;
	//var portletlname = document.form.portlet_lname.value;
	var url = "user_add_judge.jsp?user_name="+username;
	//alert(url);
	xmlHttp.onreadystatechange = handleStateChange;
	xmlHttp.open("POST",url,true);
	xmlHttp.send(null);
}

function handleStateChange(){
	if(xmlHttp.readyState == 1){
		document.getElementById("divb").innerHTML = "正在连接服务器......";
	}else if(xmlHttp.readyState == 2){
		document.getElementById("divb").innerHTML = "正在加载信息......";
	}else if(xmlHttp.readyState == 3){
		document.getElementById("divb").innerHTML = "正在交互信息......";
	
	}else if(xmlHttp.readyState == 4){
		if(xmlHttp.status == 200){//200对应ok，404对应NotFond
			document.getElementById("divb").innerHTML = unescape(xmlHttp.responseText);
			//parseString();
			//document.getElementById("weather").innerHTML = xmlHttp.responseText;
		}else{
			document.getElementById("divb").innerHTML = "出错啦"+xmlHttp.responseText;
		}
	}else{
		document.getElementById("divb").innerHTML = "网络通讯失败,请检查网络连接！";	
	}
}
function runGetText(){
	startRequest();
	//setInterval("startRequest()",5000);	
}
</script>

<span id="divb"></span>