<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>计时器</title>
<script type="text/javascript">
function clock(){
var time=new Date();
document.getElementById("clock").value = time;
}
// 每隔100毫秒调用clock函数，并将返回值赋值给i
var i=setInterval("clock()",1000);
function rec(){var i=setInterval("clock()",1000);}</script>
</head>
<body>
<form>
<input type="text" id="clock" size="50" />
<input type="button" value="Stop" onclick="clearInterval(i)" />
<input type="button" value="start" onclick="rec()"></form>
</body>
</html>
function rec(){var i=setInterval("clock()",1000);}</script> var 去掉就可以了