<BODY>
<div id="d"></div>
<script>
window.onload=function(){
var ss=0;
var mm=0;
var hh=0;
var str;
var time=window.setInterval(function(){
str="";
if(++ss==60){
if(++mm==60){
hh++;
mm=0;
}
ss=0;
}
str+=hh<10?"0"+hh:hh;
str+=":";
str+=mm<10?"0"+mm:mm;
str+=":";
str+=ss<10?"0"+ss:ss;
document.getElementById("d").innerHTML=str;
},1000);
}
</script>
</BODY>
原文：http://www.cnblogs.com/liyuhuan/p/5423830.html