<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script type="text/javascript">
var check = null;
function printDuration() {
if (check == null) {
var cnt = 0;
check = setInterval(function () {
cnt += 1;
document.getElementById("para").innerHTML = cnt;
}, 1000);
}
}
function stop() {
clearInterval(check);
check = null;
document.getElementById("para").innerHTML = '0';
}
</script>
<div>
<p id="para">0</p>
<input id="btnStart" type="button" value="Start"
onclick="printDuration();" />
<input id="btnStop" type="button" value="Stop"
onclick="stop();" />
</div>
