JavaScript实现简单倒计时器

<!DOCTYPE html >
<html>
<head>
<title>倒计时</title>

<style type="text/css">
  .colockbox
  {
   width:500px;
   height:20px; 
   color:#000000;
  }

  .colockbox span
  {
  float:left;display:block;
  width:20px;
  height:20px;
  line-height:20px;
  font-size:18px; 
  font-weight:bold;
  text-align:center;
  color:#ffffff; 
  text-indent:3px; 
  }

  .square 
  {
   float:left;
   width:26px;
   height:20px;
   background-color:#222222;
   border-radius:3px;
   padding:0px;
   margin-right:5px;
  }

</style>

<script type="text/javascript" src="jquery-1.11.3.js"></script>
<script type="text/javascript">
$(function(){
 countDown("2016/12/25 23:00:00","#colockbox1");
});
function countDown(time,id){
 var day_elem = $(id).find('.day');
 var hour_elem = $(id).find('.hour');
 var minute_elem = $(id).find('.minute');
 var second_elem = $(id).find('.second');
 var end_time = new Date(time).getTime(),//月份是实际月份-1 
 sys_second = (end_time-new Date().getTime())/1000; 
 var timer = setInterval(function(){
  if (sys_second > 1) {
   sys_second -= 1;
   var day = Math.floor((sys_second / 3600) / 24);
   var hour = Math.floor((sys_second / 3600) % 24);
   var minute = Math.floor((sys_second / 60) % 60);
   var second = Math.floor(sys_second % 60);
   day_elem && $(day_elem).text(day);//计算天
   $(hour_elem).text(hour<10?"0"+hour:hour);//计算小时
   $(minute_elem).text(minute<10?"0"+minute:minute);//计算分钟
   $(second_elem).text(second<10?"0"+second:second);//计算秒杀
  } else { 
   clearInterval(timer);
  }
 }, 1000);
}
</script>
</head>
<body>

<div class="colockbox" id="colockbox1">


<div class="square"> 
<span class="day">00</span> 
</div>
<span style="color:gray;font-size:15px; float:left;">天</span>

<div class="square"> 
<span class="hour">00</span> 
</div>
<span style="color:gray;font-size:15px; float:left;">时</span>

<div class="square"> 
<span class="minute">00</span> 
</div>
<span style="color:gray;font-size:15px; float:left;">分</span>

<div class="square"> 
<span class="second">00</span> 
</div>
<span style="color:gray;font-size:15px; float:left;">秒</span>
</div>
</body>
</html>