一：设置时长，进行倒计时。
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。
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 onl oad="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>