一个不错的js html页面倒计时可精确到秒，很简单，但和实用
<!doctype html>
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<DIV id="CountMsg" class="HotDate">
<span id="t_d">00天</span>
<span id="t_h">00时</span>
<span id="t_m">00分</span>
<span id="t_s">00秒</span>
</DIV>
<script type="text/javascript">
function getRTime(){
var EndTime= new Date('2014/10/23 10:00:00'); //截止时间
var NowTime = new Date();
var t =EndTime.getTime() - NowTime.getTime();
/*var d=Math.floor(t/1000/60/60/24);
t-=d*(1000*60*60*24);
var h=Math.floor(t/1000/60/60);
t-=h*60*60*1000;
var m=Math.floor(t/1000/60);
t-=m*60*1000;
var s=Math.floor(t/1000);*/
var d=Math.floor(t/1000/60/60/24);
var h=Math.floor(t/1000/60/60%24);
var m=Math.floor(t/1000/60%60);
var s=Math.floor(t/1000%60);
document.getElementById("t_d").innerHTML = d + "天";
document.getElementById("t_h").innerHTML = h + "时";
document.getElementById("t_m").innerHTML = m + "分";
document.getElementById("t_s").innerHTML = s + "秒";
}
setInterval(getRTime,1000);
</script>
</body>
</html>