<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<script type="text/javascript">
var num=0;
var i;
function startCount(){
document.getElementById('count').value=num;
num=num+1;
i=setTimeout(startCount,1000);
}
setTimeout(startCount,1000);
function stopCount(){
clearTimeout(i);
}
</script>
</head>
<body>
<form>
<input type="text" id="count" />
<input type="button" value="Start" onClick="startCount()"/>
<input type="button" value="Stop" onClick="stopCount()" />
</form>
</body>
</html>