倒计时：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>JS实现倒计时(时、分，秒)</title>
<script language="javascript" type="text/javascript">
var interval = 1000;
function ShowCountDown(year,month,day,divname)
{
var now = new Date();
var endDate = new Date(year, month-1, day);
var leftTime=endDate.getTime()-now.getTime();
var leftsecond = parseInt(leftTime/1000);
//var day1=parseInt(leftsecond/(24*60*60*6));
var day1=Math.floor(leftsecond/(60*60*24));
var hour=Math.floor((leftsecond-day1*24*60*60)/3600);
var minute=Math.floor((leftsecond-day1*24*60*60-hour*3600)/60);
var second=Math.floor(leftsecond-day1*24*60*60-hour*3600-minute*60);
var cc = document.getElementById(divname);
cc.innerHTML = "距离"+year+"年"+month+"月"+day+"日还有："+day1+"天"+hour+"小时"+minute+"分"+second+"秒";
}
window.setInterval(function(){ShowCountDown(2010,4,20,'divdown1');}, interval);
</script>
</head>
<body>
<div id="divdown1"></div>
</body>
</html>效果：
距离2010年4月20日还有：-2642天12小时7分37秒