<!DOCTYPE html>
<html>
<body>
<button onClick="myTimer = setInterval(myCounter, 1000)">Start counter!</button>
<p id="demo">Click on the button above and I will count forever.</p>
<button onClick="clearInterval(myTimer)">Stop counter!</button>
<script>
var c = 0;
function myCounter() {
document.getElementById("demo").innerHTML = ++c;
}
</script>
</body>
</html>