js 倒计时代码

<SCRIPT LANGUAGE="JavaScript">   var maxtime = 12*60*60; //以12小时为例  function CountDown(){   if(maxtime>=0){hours = Math.floor(maxtime/3600);minutes = Math.floor((maxtime - (hours*60*60))/60);seconds = Math.floor(maxtime%60);if(hours>0){  msg = "距离结束还有"+hours+"时"+minutes+"分"+seconds+"秒";}else if(minutes>0){  msg = "距离结束还有"+minutes+"分"+seconds+"秒";}else{  msg = "距离结束还有"+seconds+"秒";}   document.all["timer"].innerHTML=msg;--maxtime;}   else{   clearInterval(timer);   alert("时间到，结束!");}   }   timer = setInterval("CountDown()",1000);   </SCRIPT>   <div id="timer" style="color:red"></div>