Ajax长轮询

HTML code:

<script type="text/javascript">
<!--
var time = 0;
var http_request=null;
function HttpRequest(){
if (window.ActiveXObject){
http_request = new ActiveXObject("Microsoft.XMLHTTP");
}else if (window.XMLHttpRequest){
http_request = new XMLHttpRequest();
}
return http_request;
}
HttpRequest();
function autoSend(timestamp){
url = 'http://www.me.c/comet/back.php';
http_request.open('GET', url, false);
//http_request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;charset=UTF-8");
http_request.send('timestamp='+ timestamp +'&num='+Math.random());
// http_request.onreadystatuschange = CallBack;
var data = http_request.responseText;
var json = eval('('+ data +')');
alert(json.timestamp);
document.getElementById('content').innerHTML += '<div>'+json.msg +'</div>'
autoSend(json.timestamp);
}
function send(){
var msg = document.getElementById('msg').value;
var url = 'http://www.me.c/comet/back.php';
http_request.open('POST', url, false);
http_request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;charset=UTF-8");
http_request.send('msg='+msg+'&num='+Math.random()