<!DOCTYPE HTML>
<html>
<head>
<title>计时器</title>
<script type="text/javascript">
function clock(){
var time=new Date();
document.getElementById("clock").value = time;
}
var i=setInterval("clock()",100);
</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="setInterval('clock()',100)" />
</form>
</body>
</html>
2015-11-06
<!DOCTYPE HTML>
<html>
<head>
<title>计时器</title>
<script type="text/javascript">
function clock(){
var time=new Date();
document.getElementById("clock").value = time;
}
var i=setInterval("clock()",100);
var timer = null;
function start(){
if(timer){
clearInterval(timer);
timer = null;
}
setInterval('clock()',100)
}
function stop(){
if(timer){
clearInterval(timer);
timer = null;
}
}
</script>
</head>
<body>
<form>
<input type="text" id="clock" size="50" />
<input type="button" value="Stop" onclick="start()" />
<input type="button" value="Start" onclick="stop()" />
</form>
</body>
</html>因为你没有接收点按钮开启的定时的引用 那个i也不是，所以你就关不掉了
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