html页面代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<center>
<span></span>
</center>
</body>
</html>
<script src="__STATIC__/jquery-3.3.1.min.js"></script>
<script>
$(document).ready(function () {
window.setInterval(function () {
//获取当前时间
var now_time = new Date();
// alert(now_time)
//获取结束时间
var end_time = new Date(‘2018-09-20 00:00:00‘);
//计算时间差
var t = end_time.getTime() - now_time.getTime();
if (t>0){
var day = Math.floor(t/1000/60/60/24);
var hour = Math.floor(t/1000/60/60%24);
var minute = Math.floor(t/1000/60%60);
var second = Math.floor(t/1000%60);
}
$(‘span‘).html(day+"天"+hour+"小时"+minute+"分钟"+second+"秒");
},1000);
})
</script>
原文：https://www.cnblogs.com/wanglongfei/p/9720877.html