<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<span id="a">
</body>
</html>
<script>
function b(){
var a=document.getElementById("a")
var time=new Date()
var year=time.getFullYear()
var month=time.getMonth()+1
var day=time.getDay()
var hour=time.getHours()
var min=time.getMinutes()<10?"0"+time.getMinutes():time.getMinutes()
var sec=time.getSeconds()<10?"0"+time.getSeconds():time.getSeconds()
var get_time=year+"/"+month+"/"+day+"  "+hour+":"+min+":"+sec
a.innerHTML=get_time
}
window.setInterval("b()",500)
</script>
原文：http://www.cnblogs.com/hezhilong/p/7643552.html