JS Asynchronous

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript setInterval()</h2>

<p>Using setInterval() to display the time every second (1000 milliseconds).</p>

<h1 id="demo"></h1>

<script>
setInterval(myFunction, 1000);

function myFunction() {
  let d = new Date();
  document.getElementById("demo").innerHTML=
  d.getHours() + ":" +
  d.getMinutes() + ":" +
  d.getSeconds();
}
</script>

</body>
</html>