javascript有内置对象Date.
首先，声明一个变量保存当前时间：
var now=new Date();
接着得到年月日及时分秒：
now.toLocaleDateString();
now.toLocaleTimeString();
动态显示如下：
<head>
<script type="text/javascript">
function nowtime(){
var now=new Date();
document.getElementById("time").innerHTML=now.toLocaleDateString()+"<br>"+now.toLocaleTimeString();
}
setInterval("nowtime()",1000);
</script>
<script type="text/javascript">
function nowtime(){
var now=new Date();
document.getElementById("time").innerHTML=now.toLocaleDateString()+"<br>"+now.toLocaleTimeString();
}
setInterval("nowtime()",1000);
</script>
</head>
<body>
<p id="time"></p>
</body>
<body>
<p id="time"></p>
</body>