效果：
实现的代码：
<html>
<head>
<title>倒计时-木庄博客整理</title>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
</head>
<body onload="clock();return true" text="red">
距离2020年元旦还有
<br />
<!--倒计时设置代码-->
<script language="JavaScript" type="text/javascript">
<!-- hide script from old browser
var DifferenceHour = -1
var DifferenceMinute = -1
var DifferenceSecond = -1
var Tday = new Date("Jan 1, 2020 00:00:00") //**倒计时时间点-注意格式
var daysms = 24 * 60 * 60 * 1000
var hoursms = 60 * 60 * 1000
var Secondms = 60 * 1000
var microsecond = 1000
function clock()
{
var time = new Date()
var hour = time.getHours()
var minute = time.getMinutes()
var second = time.getSeconds()
var timevalue = ""+((hour > 12) ? hour-12:hour)
timevalue +=((minute < 10) ? ":0":":")+minute
timevalue +=((second < 10) ? ":0":":")+second
timevalue +=((hour >12 ) ? " PM":" AM")
var convertHour = DifferenceHour
var convertMinute = DifferenceMinute
var convertSecond = DifferenceSecond
var Diffms = Tday.getTime() - time.getTime()
DifferenceHour = Math.floor(Diffms / daysms)
Diffms -= DifferenceHour * daysms
DifferenceMinute = Math.floor(Diffms / hoursms)
Diffms -= DifferenceMinute * hoursms
DifferenceSecond = Math.floor(Diffms / Secondms)
Diffms -= DifferenceSecond * Secondms
var dSecs = Math.floor(Diffms / microsecond)
if(convertHour != DifferenceHour) document.formnow.dd.value=DifferenceHour
if(convertMinute != DifferenceMinute) document.formnow.hh.value=DifferenceMinute
if(convertSecond != DifferenceSecond) document.formnow.mm.value=DifferenceSecond
document.formnow.ss.value=dSecs
setTimeout("clock()",1000)
}
</script>
<!--BODY里面的ONLOAD注意-->
<!--实现显示-->
<form name="formnow">
<input value="1" name="dd" style="border: 0; width:36px;" size="2" type="text" />
天
<input value="1" name="hh" style="border: 0;" size="2" type="text" />
小时
<input value="1" name="mm" style="border: 0;" size="2" type="text" />
分
<input value="1" name="ss" style="border: 0;" size="2" type="text">
秒
</form>
<!--倒计时完毕-->
</body>
</html>