最近做浏览器界面倒计时，用js就实现，两种方式：
一：设置时长，进行倒计时。比如考试时间等等
代码如下：
<html><head><meta charset="UTF-8"><title>简单时长倒计时</title><SCRIPT type="text/javascript"> ???????????????????var maxtime = 60 * 60; //一个小时，按秒计算，自己调整! ??????????????function CountDown() { ???????????????if (maxtime >= 0) { ???????????????????minutes = Math.floor(maxtime / 60); ???????????????????seconds = Math.floor(maxtime % 60); ???????????????????msg = "距离结束还有" + minutes + "分" + seconds + "秒"; ???????????????????document.all["timer"].innerHTML = msg; ???????????????????if (maxtime == 5 * 60)alert("还剩5分钟"); ???????????????????????--maxtime; ???????????????} else{ ???????????????????clearInterval(timer); ???????????????????alert("时间到，结束!"); ???????????????} ???????????} ???????????timer = setInterval("CountDown()", 1000); ???????????????????????</SCRIPT></head><body><div id="timer" style="color:red"></div><div id="warring" style="color:red"></div></body></html>二：设置时间戳，进行倒计时。比如距离活动结束时间等等
代码如下：
<html> ?<head> ?????<meta charset="UTF-8"> ?????<title>js简单时分秒倒计时</title> ?????<script type="text/javascript"> ?????????function countTime() { ?????????????//获取当前时间 ?????????????var date = new Date(); ?????????????var now = date.getTime(); ?????????????//设置截止时间 ?????????????var str="2017/5/17 00:00:00"; ???????????var endDate = new Date(str); ????????????var end = endDate.getTime(); ?????????????????????????//时间差 ?????????????var leftTime = end-now; ????????????//定义变量 d,h,m,s保存倒计时的时间 ?????????????var d,h,m,s; ?????????????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); ????????????????????????????????} ?????????????//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+"秒"; ?????????????//递归每秒调用countTime方法，显示动态时间效果 ?????????????setTimeout(countTime,1000); ???????????} ?????</script> ?</head > ?<body onload="countTime()" > ?????<div> ?????????<span id="_d">00</span> ?????????<span id="_h">00</span> ?????????<span id="_m">00</span> ?????????<span id="_s">00</span> ?????</div> ?</body> ?</html>JS倒计时两种种实现方式 很不错
原文地址：https://www.cnblogs.com/dongh/p/9026433.html