JS实现的倒计时时钟

本文用javascript实现了一个倒计时时钟：

countdown.js

var test_val;

function el(id) {
if (document.getElementById) {
return document.getElementById(id);
} else if (window[id]) {
return window[id];
}
return null;
}

function UpdateDisplay()
{
   document.tform1.ctd.value = GetCountdownTime(document.tform1.cs.value);
   document.tform2.ctd.value = GetCountdownTime(document.tform2.cs.value);
   document.tform3.ctd.value = GetCountdownTime(document.tform3.cs.value);
   document.tform4.ctd.value = GetCountdownTime(document.tform4.cs.value);

test_val = el("test_val")
test_val.innerHTML = GetCountdownTime(document.tform4.cs.value);

timer1=setTimeout('UpdateDisplay()',250);
}

function GetCountdownTime(date_str)
{
return( TimeToHMS( GetSecond( new Date(date_str))));
}

/* get the countdown initial time to a specific time */
function GetSecond(date_count_to)
{
   date_now = new Date();

   time_now = date_now.getTime();
   time_count_to = date_count_to.getTime();

   if(time_now >= time_count_to )
   {
      ret_val = 0;
   }
   else
   {
      ret_val = Math.round( ( time_count_to - time_now ) / 1000.0 );
   }

   return (ret_val);
}

/* convert seconds value to H:MM:SS format */
function TimeToHMS(seconds)
{
   sec = seconds % 60;
   temp = ( seconds - sec ) / 60;

   minute = temp % 60;
   hour = (temp - minute) / 60;

   if(!(isFinite(sec) && isFinite(minute) && isFinite(hour))) /* invalid time */
   {
      return ("");
   }

   time_str = hour;
   time_str += ":";
   time_str+=(minute<10)?("0"+minute):minute;
   time_str+=":";
   time_str+=(sec<10)?("0"+sec):sec;

   return (time_str);
}

测试文件：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html"; charset="utf-8">
<title>Test the countdown function</title>

<! include the Javascript file >
<script language="JavaScript" src="countdown.js" type="text/JavaScript"></script>

</head>
<body>

Test1: <span id="timer1"></span><br>

function updateTimer1()
{
   timer1 = el("timer1")
   timer1.innerHTML = TimeToHMS(time_val1);
   time_val1--;

setTimeout('updateTimer1()', 1000);
}

updateTimer1();
// -->
</script>

Test2: <span id="timer2"></span><br>

function updateTimer2()
{
   timer2 = el("timer2")
   timer2.innerHTML = TimeToHMS(time_val2);
   time_val2--;

setTimeout('updateTimer2()', 1000);
}

updateTimer2();
// -->
</script>

Test1000: <span id="timer1000">ii</span><br>
<script>
</script>

</body>
</html>

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