纯js实现10分钟倒计时

一个简单实现倒计时的小栗子~

效果图：简陋的不能再简陋了，捂脸

代码：

 1 <!DOCTYPE HTML>
 2 <html>
 3 <head>
 4     <title> 倒计时 </title>
 5     <meta  charset="utf-8">
 6     <script type="text/javascript">
 7         window.onload = function(){
 8             var m = 9;  //分
 9             var s = 59;  //秒
10             var countdown = document.getElementById("title");
11             getCountdown();
12             setInterval(function(){ getCountdown() },1000);
13             function getCountdown (){
14                 countdown.innerHTML = "<span>"+m+"</span> ：<span>"+s+"</span>";
15                 if( m == 0 && s == 0 ){
16                     alert("倒计时结束");
17                     m = 9;
18                     s = 59;
19                 }else if( m >= 0 ){
20                     if( s > 0 ){
21                         s--;
22                     }else if( s == 0 ){
23                         m--;
24                         s = 59;
25                     }
26                 }
27             }
28         }
29     </script>
30 </head>
31 <body>
32     <h1>倒计时</h1>
33     <div id="title"></div>
34 </body>
35 </html>