<!DOCTYPE html>
<html>
<head></head>
<body>
<p id="p-id"></p>
<button onclick="clearTimeout(i)">Stop</button>
<script>
var i = setInterval(function () {clock()}, 1000);
function clock()
{
var d = new Date();
document.getElementById("p-id").innerHTML = d.toLocaleTimeString();
}
/*
run:
12:49:15 PM ... 12:49:16 PM ... 12:49:17 PM ...
*/
</script>
</body>
</html>