AJAX是集合了各种技术来解决用户体验的技术集合，使以前的技术大放光芒，
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<TITLE>an Ajax Demo</TITLE>
<script language="javascript">
//浏览器内部对象xmlhttprequest
var XMLHttpRequestObject = false;//声明javascript 的对象，用于
//创建xmlhttprequest对象，判断浏览器的支持种类，
if(window.XMLHttpRequest){
XMLHttpRequestObject = new XMLHttpRequest();
}
else if(window.ActiveXObject){
XMLHttpRequestObject = new ActiveXObject("Microsoft.XMLHTTP");
}
//
function getData(dataSource,divID)
{
if(XMLHttpRequestObject){
var obj = document.getElementById(divID);
XMLHttpRequestObject.open("GET",dataSource);//open方法建立服务器调用，
//回调函数
XMLHttpRequestObject.onreadystatechange = function()
{
if(XMLHttpRequestObject.readyState == 4 && XMLHttpRequestObject.status == 200){
obj.innerHTML = XMLHttpRequestObject.responseText;
}
}
XMLHttpRequestObject.send(null);//向服务器发送请求，
}
}
</script>
</head>
<body >
<h1>AN AJACX DEMO</h1>
<form >
<input type ="button" value = "fetch the message" onClick="getData('data.txt','targetDiv')">
</form>
<div id = "targetDiv">
<p>the fetched message will appear here.</p>
</div>
</body>
</html>