javascript倒計時時間代碼怎麽寫 比如在頁面上顯示3，2，1

<meta http-equiv="Page-Enter" content="revealTrans(duration=10, transition=4)"><SCRIPT LANGUAGE="JavaScript">

var maxtime ="3";

function CountDown(){

if(maxtime>=0){

minutes = Math.floor(maxtime/60);

seconds = Math.floor(maxtime%60);

msg = "妳的文字說明"+minutes+"分"+seconds+"秒";//動態顯示剩余時間。

document.all["timer"].innerHTML=msg;

//if(maxtime == 3) document.all["timer"].innerHTML='只剩3秒！';

--maxtime;

}

else{

clearInterval(timer);

document.all["timer"].innerHTML='123';

}

}

timer = setInterval("CountDown()",1000);

</SCRIPT>

<div id=timer></div>