actualizar los segundos

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript new Date()</h2>


<p id="demo"></p>

<script>
setInterval(myFunction,1000);

function myFunction() {
  let d = new Date();


document.getElementById("demo").innerHTML = d.getSeconds();
setInterval(myFunction,1000);
}
</script>

</body>
</html>
Xanthous Xenomorph