JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  Timer: <span id=timer>0</span>
</div>

JavaScript

function startTimer(secs) {
  var i = 0;
  var timer = document.getElementById('timer');

  var interval = setInterval(function() {
    if (++i >= secs) {
      clearInterval(interval);
      timer.innerHTML = 'Done!';
    } else {
      ++timer.innerHTML;
    }
  }, 1000);
}

startTimer(10);