<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
*{
margin: 0;
padding: 0;
}
</style>
</head>
<body>
<p>
<span class="m">10</span>"
<span class="s">05</span>
</p>
<br />
<br />
<input type="button" value="开始" />
<script>
var btn = document.querySelector('input');
var mText = document.querySelector('.m').innerHTML;
var sText = document.querySelector('.s').innerHTML;
var s
var m
m = goNumber(mText);
s = goNumber(sText);
var timer
btn.onclick=function(){
if( this.value == '开始' ){
timer = setInterval(timeGo,1000);
this.value = '暂停';
}else{
clearInterval(timer);
this.value = '开始';
}
}
function timeGo(){
s--
if( s < 0 ){
if( m == 0 ){
clearInterval(timer);
s++
}else{
s = 59
m--
if( m >= 0 && m < 10 ){
m = '0' + m;
}
document.querySelector('.m').innerHTML = m;
}
}
if( s >= 0 && s < 10 ){
s = '0' + s;
}
document.querySelector('.s').innerHTML = s;
}
function goNumber(str){
var number = parseInt(str);
return number;
}
</script>
</body>
</html>
![](https://images2015.cnblogs.com/blog/982650/201612/982650-20161223111704886-424735728.png)