比较简单，直接贴上代码：
<!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" xml:lang="en" lang="en">
<head>
<title>clock</title>
<script type="text/javascript">
var enable=0,tm;
function setTime(){
var now=new Date();
var time=now.toLocaleString();
document.getElementById("time").value=time;
tm=setTimeout("setTime()",1000);
enable=1;
}
</script>
</head>
<body>
<input type="text" id="time" style="overflow:visible" value="" />
<input type="button" value="开" onclick="if(enable==0){setTime();}"/>
<input type="button" value="关" onclick="if(enable==1){time.value='';clearTimeout(tm);enable=0}" />
</body>
</html>
