JSFiddle - React, Tailwind, and code Playground

HTML

<div id="timer"></div>
<p>
  Text for typing test will go here. </p>
<textarea onkeypress="myFunction()" id="textarea" rows="14" cols="150" placeholder="Start typing here..."></textarea>
<script>
  var counter = 0;

  function startTimer(duration, display) {
    var timer = duration,
      minutes, seconds;
    setInterval(function() {
      minutes = parseInt(timer / 60, 10)
      seconds = parseInt(timer % 60, 10);

      minutes = minutes < 10 ? "0" + minutes : minutes;
      seconds = seconds < 10 ? "0" + seconds : seconds;

      display.textContent = minutes + ":" + seconds;

      if (--timer < 0) {
        alert("You type " + counter + " WPM");
        timer = duration;
      }
    }, 1000);
  }

  function myFunction() {
    if (counter == 0) {
      var oneMinute = 60,
        display = document.querySelector('#timer');
      startTimer(oneMinute, display);
      counter++;
    } else {
      counter++;
    }
  };

</script>