<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>js时分秒毫秒倒计时</title>
</head>
<body>
<div>
<span id="_d">00</span>
<span id="_h">00</span>
<span id="_m">00</span>
<span id="_s">00</span>
<!--<span id="_ms">00</span>-->
</div>
<script type="text/javascript">
function countTime() {
var date = new Date();
var now = date.getTime();
var endDate = new Date("2020-10-20 18:28:00");//设置截止时间
var end = endDate.getTime();
var leftTime = end - now; //时间差
var d, h, m, s, ms;
var timer;
if(leftTime >= 0) {
d = Math.floor(leftTime / 1000 / 60 / 60 / 24);
h = Math.floor(leftTime / 1000 / 60 / 60 % 24);
m = Math.floor(leftTime / 1000 / 60 % 60);
s = Math.floor(leftTime / 1000 % 60);
ms = Math.floor(leftTime % 10);
// if(ms < 10) {
// ms = "0" + ms;
// }
if(s < 10) {
s = "0" + s;
}
if(m < 10) {
m = "0" + m;
}
if(h < 10) {
h = "0" + h;
}
//将倒计时赋值到div中
document.getElementById("_d").innerHTML = d + "天";
document.getElementById("_h").innerHTML = h + "时";
document.getElementById("_m").innerHTML = m + "分";
document.getElementById("_s").innerHTML = s + ‘.‘ + ms +"秒";
// document.getElementById("_ms").innerHTML = ms + "毫秒";
// document.getElementById("_ms").innerHTML = ms
//递归每秒调用countTime方法，显示动态时间效果
timer = setTimeout(countTime, 50);
} else {
console.log(‘已截止‘)
document.getElementById("_d").innerHTML ="00天";
document.getElementById("_h").innerHTML ="00时";
document.getElementById("_m").innerHTML ="00分";
document.getElementById("_s").innerHTML ="00秒";
// document.getElementById("_ms").innerHTML = "00毫秒";
}
}
countTime();
</script>
</body>
</html>
原文：https://www.cnblogs.com/eric-share/p/13737117.html