直接上代码
<!DOCTYPE html><html lang="en"><head> ???<meta charset="UTF-8"> ???<title>Document</title></head><body> ???<div> ???????<span id="h">00</span> ???????<span>:</span> ???????<span id="m">00</span> ???????<span>:</span> ???????<span id="s">10</span> ???</div> ???<script type="text/javascript"> ???function setId(id) { ???????return document.getElementById(id); ???} ???var hText = setId(‘h‘); ???var mText = setId(‘m‘); ???var sText = setId(‘s‘); ???var timer; ???var hour =parseInt(hText.innerHTML); ???var min = parseInt(mText.innerHTML); ???var sec = parseInt(sText.innerHTML); ???var all = hour * 60 * 60 + min * 60 + sec; ???function time() { ???????all--; ???????h = Math.floor(all / 60 / 60 % 24); ???????m = Math.floor(all / 60 % 60); ???????s = Math.floor(all % 60); ???????if (all > 0) { ???????????hText.innerHTML = isZero(h); ???????????mText.innerHTML = isZero(m); ???????????sText.innerHTML = isZero(s); ???????} else { ???????????hText.innerHTML = ‘00‘; ???????????mText.innerHTML = ‘00‘; ???????????sText.innerHTML = ‘00‘; ???????????clearInterval(timer); ???????} ???} ???function isZero(num) { ???????return num < 10 ? ‘0‘ + num : num ???} ???timer = setInterval(time, 1000); ???</script></body></html>原生js倒计时
原文地址：https://www.cnblogs.com/chenmiaosong/p/8384323.html