倒計時
<!DOCTYPE HTML>
<html>
<head>
<title> 倒計時 </title>
<meta charset="utf-8">
<script type="text/javascript">
window.onload = function(){
var m =1; //分
var s = 59; //秒
var countdown = document.getElementById("title");
getCountdown();
setInterval(function(){ getCountdown() },1000);
function getCountdown (){
countdown.innerHTML = "<span>"+m+"</span> ：<span>"+s+"</span>";
if( m == 0 && s == 0 ){
alert("倒計時結束");
m = 9;
s = 59;
}else if( m >= 0 ){
if( s > 0 ){
s--;
}else if( s == 0 ){
m--;
s = 59;
}
}
}
}
</script>
</head>
<body>
<h1>倒計時</h1>
<div id="title"></div>
</body>
</html>