<!DOCTYPE html>
<html>
<body>
<p id="demo">Clock</p>
<button onclick="clearInterval(myTimer)">Stop</button>
<script>
var myTimer = setInterval(myClock, 1000);
function myClock() {
document.getElementById("demo").innerHTML =
new Date().toLocaleTimeString();
}
</script>
</body>
</html>