描述：在页面上显示距离某一时间还有几天几时几分几秒
示例代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>倒计时</title>
<style>
.time{
width: 1200px;
margin: 200px auto;
color: red;
text-align: center;
font: 600 30px/30px "simsun";
}
</style>
</head>
<body>
<div class="time"></div>
</body>
</html>
<script>
var time = document.getElementsByClassName("time")[0];
var timer = setInterval(fn,1);
function fn() {
var nowTime = new Date();
var future = new Date("2018/11/23 00:00:00");
var timeSum = future.getTime() - nowTime.getTime();
var day = parseInt(timeSum/1000/60/60/24);
var hour = parseInt(timeSum/1000/60/60%24);
var minu = parseInt(timeSum/1000/60%60);
var sec = parseInt(timeSum/1000%60);
var millsec = parseInt(timeSum%1000);
day = day<10 ?"0"+day:day;
hour = hour<10? "0"+hour:hour;
minu = minu<10?"0"+minu:minu;
sec = sec<10?"0"+sec:sec;
if(millsec<10){
millsec = "00"+millsec;
}else if(millsec<100){
millsec = "0"+millsec;
}
if(timeSum<0){
time.innerHTML = "距离孙肖宁的生日还有00天00小时00分00秒000毫秒";
clearInterval(timer);
return;
}else {
time.innerHTML = "距离孙肖宁的生日还有"+day+"天"+hour+"小时"+minu+"分"+sec+"秒"+millsec+"毫秒";
}
}
</script>