如何让JS时间的秒随时在动 _JavaScript

怎么让JS时间的秒随时在动
today=new Date();
var hours = today.getHours();
var minutes = today.getMinutes();
var seconds = today.getSeconds();
var timeValue = ((hours >12) ? hours -12 :hours);
timeValue += ((minutes < 10) ? "<BLINK>:</BLINK>0" : "<BLINK>:</BLINK>") + minutes;
timeValue += ((seconds < 10) ? "<BLINK>:</BLINK>0" : "<BLINK>:</BLINK>") + seconds;
timeValue += (hours >= 12) ? "<B>pm</B>" : "<B>am</B>";

function initArray(){
this.length=initArray.arguments.length
for(var i=0;i<this.length;i++)
this[i+1]=initArray.arguments[i]}

var d=new initArray("星期日","星期一","星期二","星期三","星期四","星期五","星期六");
document.write(today.getYear(),"年",today.getMonth()+1,"月",today.getDate(),"日",d[today.getDay()+1]," ",timeValue)

显示时是静态的··想让时间成动态，秒随时在动··
怎么弄？

------解决方案--------------------

HTML code

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<body>
<div id=x></div>
<script>
function show()
{
today=new Date();
var hours = today.getHours();
var minutes = today.getMinutes();
var seconds = today.getSeconds();
var timeValue = ((hours >12) ? hours -12 :hours); 
timeValue += ((minutes < 10) ? "<BLINK>:</BLINK>0" : "<BLINK>:</BLINK>") + minutes;
timeValue += ((seconds < 10) ? "<BLINK>:</BLINK>0" : "<BLINK>:</BLINK>") + seconds;
timeValue += (hours >= 12) ? "<B>pm</B>" : "<B>am</B>";


var d=["星期日","星期一","星期二","星期三","星期四","星期五","星期六"];
document.getElementById("x").innerHTML=today.getFullYear() + "年" + (today.getMonth()+1) + "月"+today.getDate()+"日"+d[today.getDay()] + " " + timeValue;
}
window.onload=function()
{
 setInterval("show()",1000);
}
</script>
</body>
</html>

------解决方案--------------------
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window.onload=function()
这句干嘛用的？