如何显示来访者停留时间的js代码

<script language=javascript>
/**
 * 获取访问者的停留时间
 * Edit www.jb200.com
*/
var timerID=null
function showtime(seed){
if (seed>=0){
seed++;
mod=seed%3600;
hours=(seed-mod)/3600
seconds=mod%60
minutes=(seed-3600*hours-seconds)/60;
var timeValue=""+((hours < 10)?"0":"")+hours
timeValue+=((minutes < 10)?":0":":")+minutes
timeValue+=((seconds < 10)?":0":":")+seconds
document.clock.face.value=timeValue;
var cmd="showtime("+seed+")";
timeID=window.setTimeout(cmd,1000); }}
</script>

onload=showtime(0)

<form name=clock>
<input name=face style="font-size: 9pt;color:#000000;border:0" size=7>
</form>