JavaScript 实现电子时钟倒计时功能详解

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>电子时钟</title>
 <style type="text/css">
 *{
 margin: 0;
 padding: 0;
 }
 #wrap{
  width: 200px;
  height: 100px;
  background-color: black;
 }
 #time{
  color: #fff;
  display: block;
  font-size: 24px;
  margin: 0 auto;
  padding-top: 20px;
  /*border: 1px solid red;*/
  text-align: center;
  width: 100px;
 }
 #timer{
  color: green;
  display: block;
  font-size: 18px;
  margin: 0 auto;
  padding-top: 10px;
  /*border: 1px solid red;*/
  text-align: center;
  /*width: 100px;*/
 }
 </style>
</head>
<body>
 <div id="wrap">
  <span id="time"></span>
  <span id="timer"></span>
 </div>
 <script type="text/javascript">
 var time =document.getElementById("time");
 var timer =document.getElementById("timer");

 setInterval(function() {

 var date = new Date();
 var hours = date.getHours();
 var minutes = date.getMinutes();
 var seconds = date.getSeconds(); 
 var years = date.getYear();
 var dates = date.getDate();
 var monts = date.getMonth()+1; 
 var day = date.getDay();
 var parses = date.getMilliseconds()%60;

 switch(day){
  case 0:
  day="日";
  case 1:
  day="一";
  case 2:
  day="二";
  case 3:
  day="三";
  case 4:
  day="四";
  case 5:
  day="五";
  case 6:
  day="六";
 }
 //如果秒数小于十，在秒数面前连接一个0
 if(seconds < 10) {
  seconds = "0" + seconds;
 }
 //如果分钟数小于十，在分钟数面前连接一个0
 if(minutes < 10) {
  minutes = "0" + minutes;
 }
 //如果小时数小于十，在小说数面前连接一个0
 if(hours < 10) {
  hours = "0" + hours;
 }
 if(years<1900) {
  years = years+1900;
 }
 if(dates<10) {
  dates = "0" + dates;
 }
 if(monts<10) {
  monts = "0" + monts;
 }
 if(parses<10) {
  // parses = "0" + parses;
 }

 
 timer.innerHTML = years +"年" +monts+ "月" +dates +"号"+"星期"+day;
  time.innerHTML = hours + ":" + minutes + ":" + seconds + ":" + parses;
 // date.getTime()//返回的是一个从1970年到当前的毫秒数（时间戳）（ms）
 // date.getMonth()//返回的是月份，从0开始算
 // date.getFullYear();
 
 },10)
 </script>
</body>
</html>