runCount(10);
function runCount(t){
  if(t>0){
    document.getElementById(‘shownum').innerHTML = t;
    t–;
    setTimeout(function(){runCount(t);},1000);
  }else{
    document.getElementById(‘shownum').innerHTML = ‘倒计时结束！';
  }
}

<div>
  距明年还有:
  <span id='daya'></span>天
  <span id='hoursa'></span>小时
  <span id='minua'></span>分
  <span id='secoa'></span>秒
</div>
<script type="text/javascript">
/**
*
*  copyright WE 2012.7
*  js实现动态倒计时功能
*  a是从后台接收到的时间戳，需转换成毫秒单位
*
*/
  var a=12345678;     //以毫秒为单位
  function fomtime()
  {
    a=a-1000;
    var b=new Date();
    b.setTime(0);
    var c=new Date();
    c.setTime(a);
    var day1=b.getDate();    //为方便调用，把天数、小时等单独定义
    var hours1=b.getHours();
    var minu1=b.getMinutes();
    var seco1=b.getSeconds();
    var day2=c.getDate();
    var hours2=c.getHours();
    var minu2=c.getMinutes();
    var seco2=c.getSeconds();
    var day=day2-day1;
    var hours=hours2-hours1;
    var minu=minu2-minu1;
    var seco=seco2-seco1;
    document.getElementById('daya').innerHTML=day;
    document.getElementById('hoursa').innerHTML=hours;
    document.getElementById('minua').innerHTML=minu;
    document.getElementById('secoa').innerHTML=seco;
    setTimeout("fomtime()",1000);
  }
  fomtime();
</script>

<Script Language="JavaScript">  
<!-- Begin  
 var timedate= new Date("January 14,2006");  
 var times="研究生考试";  
 var now = new Date();  
 var date = timedate.getTime() - now.getTime();  
 var time = Math.floor(date / (1000 * 60 * 60 * 24));  
 if (time >= 0) ; 
 document.write("<li><font color=#DEDBDE>现在离2006年"+times+"还有: <font color=#ffffff><b>"+time +"</b></font> 天</font></li>"); 
// End --> 
</Script> 

<script language="JavaScript" type="text/javascript"> 
function djs(){ 
 var urodz= new Date("11/12/2008"); 
 var now = new Date(); 
 var num 
 var ile = urodz.getTime() - now.getTime(); 
 var dni = Math.floor(ile / (1000 * 60 * 60 * 24)); 
 if (dni >1)num=dni+1
 else if (dni == 1)num=2 
 else if (dni == 0)num=1
 else num=0 
 document.write(num) 
} 
</script> 

<form name="form1"> 
<div align="center" align="center"> 
<center>离2013年还有:<br> 
<input type="textarea" name="left" size="35" style="text-align: center"> 
</center> 
</div> 
</form> 
<script LANGUAGE="javascript"> 
 startclock() 
 var timerID = null; 
 var timerRunning = false; 
 function showtime() { 
  Today = new Date(); 
  var NowHour = Today.getHours(); 
  var NowMinute = Today.getMinutes(); 
  var NowMonth = Today.getMonth(); 
  var NowDate = Today.getDate(); 
  var NowYear = Today.getYear(); 
  var NowSecond = Today.getSeconds(); 
  if (NowYear <2000) 
  NowYear=1900+NowYear; 
  Today = null; 
  Hourleft = 23 - NowHour 
  Minuteleft = 59 - NowMinute 
  Secondleft = 59 - NowSecond 
  Yearleft = 2009 - NowYear 
  Monthleft = 12 - NowMonth - 1
  Dateleft = 31 - NowDate 
  if (Secondleft<0) 
  { 
   Secondleft=60+Secondleft; 
   Minuteleft=Minuteleft-1; 
  } 
  if (Minuteleft<0) 
  {  
   Minuteleft=60+Minuteleft; 
   Hourleft=Hourleft-1; 
  } 
  if (Hourleft<0) 
  { 
   Hourleft=24+Hourleft; 
   Dateleft=Dateleft-1; 
  } 
  if (Dateleft<0) 
  { 
   Dateleft=31+Dateleft; 
   Monthleft=Monthleft-1; 
  } 
  if (Monthleft<0) 
  { 
   Monthleft=12+Monthleft; 
   Yearleft=Yearleft-1; 
  } 
  Temp=Yearleft+'年, '+Monthleft+'月, '+Dateleft+'天, '+Hourleft+'小时, '+Minuteleft+'分, '+Secondleft+'秒'
  document.form1.left.value=Temp; 
  timerID = setTimeout("showtime()",1000); 
  timerRunning = true; 
 } 
 var timerID = null; 
 var timerRunning = false; 
 function stopclock () { 
  if(timerRunning) 
   clearTimeout(timerID); 
  timerRunning = false; 
 } 
 function startclock () { 
  stopclock(); 
  showtime(); 
 } 
// --> 
</script> 

<!--倒计时Javascript begin--> 
<script language="JavaScript"> 
<!--  
function DigitalTime1() 
{  
 var deadline= new Date("08/13/2007") //开幕倒计时 
 var symbol="8月13日"
 var now = new Date() 
 var diff = -480 - now.getTimezoneOffset() //是北京时间和当地时间的时间差 
 var leave = (deadline.getTime() - now.getTime()) + diff*60000
 var day = Math.floor(leave / (1000 * 60 * 60 * 24)) 
 var hour = Math.floor(leave / (1000*3600)) - (day * 24) 
 var minute = Math.floor(leave / (1000*60)) - (day * 24 *60) - (hour * 60) 
 var second = Math.floor(leave / (1000)) - (day * 24 *60*60) - (hour * 60 * 60) - (minute*60) 

 var deadline_2= new Date("08/13/2004") //开幕后计时 
 var symbol_2="8月13日"
 var now_2 = new Date() 
 var diff_2 = -480 - now.getTimezoneOffset() //是北京时间和当地时间的时间差 
 var leave_2 = (now_2.getTime() - deadline_2.getTime()) + diff_2*60000
 var day_2 = Math.floor(leave_2 / (1000 * 60 * 60 * 24)) 
 var hour_2 = Math.floor(leave_2 / (1000*3600)) - (day_2 * 24) 
 var minute_2 = Math.floor(leave_2 / (1000*60)) - (day_2 * 24 *60) - (hour_2 * 60) 
 var second_2 = Math.floor(leave_2 / (1000)) - (day_2 * 24 *60*60) - (hour_2 * 60 * 60) - (minute_2*60) 

 day=day+1; 
 day_2=day_2+1; 

 if (day>0) //还未开幕 
 { 
  //LiveClock1.innerHTML = "现在"+symbol+"天" 
  LiveClock1.innerHTML = "<font
  setTimeout("DigitalTime1()",1000) 
 } 

 if (day<0) //已经开幕 
 { 
  //LiveClock1.innerHTML = "现在离"+symbol+"还有"+day+"天"+hour+"小时"+minute+"分"+second +"秒" 
  LiveClock1.innerHTML = "<font
  setTimeout("DigitalTime1()",1000) 
 } 

 if (day==0) //正在开幕 
 { 
  //LiveClock1.innerHTML = "现在"+symbol+"天" 
  LiveClock1.innerHTML = "<font
  setTimeout("DigitalTime1()",1000) 
 } 

 if (day<0 & day_2>19) //某某运动会结束 
 { 
  //LiveClock1.innerHTML = "现在离"+symbol+"还有"+day+"天"+hour+"小时"+minute+"分"+second +"秒" 
  LiveClock1.innerHTML = "<font
  setTimeout("DigitalTime1()",1000) 
 } 

} 
// --> 
</script> 
<!--倒计时Javascript end--> 
<body onload=DigitalTime1()> 
<div id= LiveClock1></div> 

</body>

<SCRIPT LANGUAGE="JavaScript"> 
<!-- 
var maxtime = 60*60 //一个小时，按秒计算，自己调整! 
function CountDown(){ 
 if(maxtime>=0){ 
  minutes = Math.floor(maxtime/60); 
  seconds = Math.floor(maxtime%60); 
  msg = "距离结束还有"+minutes+"分"+seconds+"秒"; 
  document.all["timer"].innerHTML=msg; 
  if(maxtime == 5*60) 
   alert('注意，还有5分钟!'); 
  --maxtime; 
 } 
 else{ 
  clearInterval(timer); 
  alert("时间到，结束!"); 
 } 
} 
timer = setInterval("CountDown()",1000); 
//--> 
</SCRIPT> 
<div id="timer" style="color:red"></div> 

<span id="clock">00:01:11:00</span> 
<input id="startB" type="button" value="start countdown!" onclick="run()"> 
<input id="endB" type="button" value="stop countdown!" onclick="stop()"> 
<br> 
<input id="diff" type="text"> 
<input id="next" type="text"> 
<script language="Javascript"> 
var normalelapse = 100; 
var nextelapse = normalelapse; 
var counter;  
var startTime; 
var start = clock.innerText;  
var finish = "00:00:00:00"; 
var timer = null; 

// 开始运行 
function run() { 
 startB.disabled = true; 
 endB.disabled = false; 
 counter = 0; 
 // 初始化开始时间 
 startTime = new Date().valueOf(); 

 // nextelapse是定时时间, 初始时为100毫秒 
 // 注意setInterval函数: 时间逝去nextelapse(毫秒)后, onTimer才开始执行 
 timer = window.setInterval("onTimer()", nextelapse);  
} 

// 停止运行 
function stop() { 
 startB.disabled = false; 
 endB.disabled = true; 
 window.clearTimeout(timer); 
} 

window.onload = function() { 
 endB.disabled = true; 
};

// 倒计时函数 
function onTimer() 
{ 
 if (start == finish) 
 { 
  window.clearInterval(timer); 
  alert("time is up!"); 
  return; 
 } 

 var hms = new String(start).split(":"); 
 var ms = new Number(hms[3]); 
 var s = new Number(hms[2]); 
 var m = new Number(hms[1]); 
 var h = new Number(hms[0]); 

 ms -= 10; 
 if (ms < 0) 
 { 
  ms = 90; 
  s -= 1; 
  if (s < 0) 
  { 
    s = 59; 
    m -= 1; 
  } 

  if (m < 0) 
  { 
    m = 59; 
    h -= 1; 
  } 
 } 

 var ms = ms < 10 "0" + ms) : ms; 
 var ss = s < 10 "0" + s) : s; 
 var sm = m < 10 "0" + m) : m; 
 var sh = h < 10 "0" + h) : h; 

 start = sh + ":" + sm + ":" + ss + ":" + ms; 
 clock.innerText = start; 

 // 清除上一次的定时器 
 window.clearInterval(timer); 

 // 自校验系统时间得到时间差, 并由此得到下次所启动的新定时器的时间nextelapse 
 counter++;  
 var counterSecs = counter * 100; 
 var elapseSecs = new Date().valueOf() - startTime; 
 var diffSecs = counterSecs - elapseSecs; 
 nextelapse = normalelapse + diffSecs; 
 diff.value = counterSecs + "-" + elapseSecs + "=" + diffSecs; 
 next.value = "nextelapse = " + nextelapse; 
 if (nextelapse < 0) nextelapse = 0; 

 // 启动新的定时器 
 timer = window.setInterval("onTimer()", nextelapse);  
} 
</script>