JavaScript实现刷新不重记的倒计时

<!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=utf-8" />
<title>js倒计时-刷新不重计</title>
</head>
 
<body>
<SCRIPT LANGUAGE="JavaScript">
<!--
var maxtime;
if(window.name==''){ 
 maxtime = 1*60;
 }else{
 maxtime = window.name;
}
 
function CountDown(){
 if(maxtime>=0){
 minutes = Math.floor(maxtime/60);
 seconds = Math.floor(maxtime%60);
 msg = "距离考试结束还有"+minutes+"分"+seconds+"秒";
// document.all["timer"].innerHTML = msg;
 document.getElementById("timer").innerHTML = msg;
 if(maxtime == 5*60) alert('注意，还有5分钟!');
 --maxtime;
 window.name = maxtime; 
 }
 else{
 clearInterval(timer);
 alert("考试时间到，结束!");
 }
}
timer = setInterval("CountDown()",1000);
//-->
</SCRIPT>
<div id="timer" style="color:red"></div> 
 
</body>
</html>