Untitled

<!DOCTYPE HTML>
<html>
<head>
        <meta charset="utf-8">
        <title>rafal</title>
</head>
<body>
 <form name="form_main">
  <div>
    <span id="hour">00</span>:<span id="minute">00</span>:<span id="second">00</span>:<span id="millisecond">000</span> <br>
  </div>

  <button type="button" id="start" name="start">kilk1</button>

</form>
<script>
let hour = 0;
let minute = 0;
let second = 0;
let millisecond = 0;

let cron;

document.form_main.start.onclick = () => start();
document.getElementById("start").ondblclick = function() { pause() };


function start() {
  pause();
  cron = setInterval(() => { timer(); }, 10);
}

function pause() {
  clearInterval(cron);
}

function reset() {
  hour = 0;
  minute = 0;
  second = 0;
  millisecond = 0;
  document.getElementById('hour').innerText = '00';
  document.getElementById('minute').innerText = '00';
  document.getElementById('second').innerText = '00';
  document.getElementById('millisecond').innerText = '000';
}

function timer() {
  if ((millisecond += 10) == 1000) {
    millisecond = 0;
    second++;
  }
  if (second == 60) {
    second = 0;
    minute++;
  }
  if (minute == 60) {
    minute = 0;
    hour++;
  }
  document.getElementById('hour').innerText = returnData(hour);
  document.getElementById('minute').innerText = returnData(minute);
  document.getElementById('second').innerText = returnData(second);
  document.getElementById('millisecond').innerText = returnData(millisecond);
}

function returnData(input) {
  return input >= 10 ? input : `0${input}`
}

</script>


</html>