JSFiddle - React, Tailwind, and code Playground

HTML

<div id="counter"></div>

JavaScript

document.addEventListener('DOMContentLoaded', function()
{
  var count = document.querySelector('#counter'),
  sec = 1000,
  load = Date.now();
  setTimeout(function tick()
  {
    var now = ((Date.now()-load)/sec) | 0,
    pas = timePassed(now);
    count.innerHTML = pas;
    setTimeout(tick, sec);
  }, sec);
});

function timePassed(now)
{
  var hh = String(now/3600 | 0).padStart(2, '0'),
  mm = String((now/60 | 0) % 60).padStart(2, '0'),
  ss = String(now % 60).padStart(2, '0');
  return (hh+':'+mm+':'+ss);
}