<html>
<body>
<script>
var a=100;
function showtime(){
a--;
document.getElementById("p_miao").innerHTML=Math.floor(a/60)+":"+a%60;
if(a<=0){
alert("时间已到");
}
setTimeout("showtime()",1000);
}
setTimeout("showtime()",1000);
</script>
<p id="p_miao"></p>
</body>
</html>
