XMLHttpRequest对象中与标头有关的方法：
setRequestHeader(<header>,<value>)——用指定值设置标头。
getResponseHeader(<header>)——获取指定标头的值;
getAllResponseHeaders()——以单个字符串形式获取全部标头。
覆盖请求的HTTP方法，例如以下代码：可规避防火墙仅仅同意GET和POST请求通过的限制；
httpRequest.setRequestHeader("X-HTTP-Method-Override","DELETE");禁用内容缓存：
httpRequest.setRequestHeader("Cache-Control","no-cache");<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="UTF-8">
<title>上海远地资产管理有限公司</title>
<meta name="author" content="jason"/>
<meta name="description" content="上海远地资产管理有限公司（简称：远地资产），是一家专业的互联网金融服务平台."/>
<link rel="shortcut icon" href="images/favicon.ico" type="image/x-icon"/>
<style type="text/css">
#allheaders,#ctheader{
border: medium solid black;
padding: 2px;
margin: 2px;
}
</style>
</head>
<body>
<div>
<button>Apples</button>
<button>Cherries</button>
<button>Bananas</button>
</div>
<div id="ctheader"></div>
<div id="allheaders"></div>
<div id="target">
载入内容
</div>
</table>
<script>
var buttons=document.getElementsByTagName("button");
for(var i=0;i<buttons.length;i++){
buttons[i].onclick=handleButtonPress;
}
var httpRequest;
function handleButtonPress(e){
httpRequest=new XMLHttpRequest();
httpRequest.onreadystatechange=handleResponse;
httpRequest.open("GET", e.target.innerHTML+".html");
//规避防火墙的限制，使用X-HTTP-Method-Override标头来指定想要的HTTP方法，但形式上市再发送一个POST请求
//httpRequest.setRequestHeader("X-HTTP-Method-Override","DELETE");
//禁用内容缓存
//httpRequest.setRequestHeader("Cache-Control","no-cache");
httpRequest.send();
}
function handleResponse(){
if(httpRequest.readyState==2){
document.getElementById("allheaders").innerHTML=httpRequest.getAllResponseHeaders();
document.getElementById("ctheader").innerHTML=httpRequest.getResponseHeader("Content-Type");
}else if(httpRequest.readyState==4 && httpRequest.status==200){
document.getElementById("target").innerHTML= httpRequest.responseText;
}
}
</script><pre name="code" class="html"></body>
</html>