work_clock.html

<style>
#clock {
  font-size: 70px;
    
 }

</style>

<div id="clock">
  <span class="hour">hh</span>:<span class="min">mm</span>:<span class="sec">ss</span>
</div>

<script>
var timerId;  

function update () {
  var clock = document.getElementById('clock')
  var date = new Date ();
  
  var hours = date.getHours();
  if(hours < 10) hours = '0' + hours;
  clock.children[0].innerHTML = hours;
 
 
  var minutes = date.getMinutes();
  if(minutes < 10) minutes = '0' + minutes;
  clock.children[1].innerHTML = minutes;
  
  var seconds = date.getSeconds();
  if(seconds < 10) seconds = '0' + seconds;
  clock.children[2].innerHTML = seconds;

}
function startClock() {

  update();
  timerId = setInterval(update, 1000);
  }

startClock();

// function stopClock() {
//   clearInterval(timerId)
//   timerId = null;
// }

// stopClock();



</script>