JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en-US">
  <head>
    <meta charset="utf-8">
    <title>Simple setInterval clock</title>
    <style>
      p {
        font-family: sans-serif;
      }
    </style>
  </head>
  <body>
    <div id="root"></div>
  </body>
</html>

JavaScript

class TimerView {
  constructor() {
  	this.rootElement = document.createElement('div');
    this.rootElement.classList.add('timer');
    
    this.startButton = document.createElement('button');
    this.startButton.classList.add('timer__start-button');
    this.startButton.textContent = 'Start';
    
    this.stopButton = document.createElement('button');
    this.stopButton.classList.add('timer__stop-button');
    this.stopButton.textContent = 'Stop';
    this.stopButton.disabled = true;
    
    this.resetButton = document.createElement('button');
    this.resetButton.textContent = 'Reset';
    this.resetButton.classList.add('timer__reset-button');
    
    this.elapsedTimeElement = document.createElement('p');
    this.elapsedTimeElement.classList.add('timer__elapsed-time');
    this.elapsedTimeElement.textContent = '0';
    
    this.rootElement.append(this.startButton, this.stopButton, this.resetButton, this.elapsedTimeElement);
 	}
  
  onStart(callback) {
  	this.startButton.addEventListener('click', () => {
    	this.startButton.disabled = true;
      this.stopButton.disabled = false;
    	callback(this);
    });
  }
  
  onStop(callback) {
  	this.stopButton.addEventListener('click', () => {
    	this.startButton.disabled = false;
      this.stopButton.disabled = true;
    	callback(this);
    });
  }
  
  onReset(callback) {
  	this.resetButton.addEventListener('click', () => {
    	this.startButton.disabled = false;
      this.stopButton.disabled = true;
    	callback(this);
    });
  }
  
	set elapsedTime(value) {
    this.elapsedTimeElement.textContent = value;
  }
  
  get root() {
  	return this.rootElement;
  }
}

let startTime;
let createClock;
let createStopClock;
let pauseTime = 0;
let startPauseTime = 0;

const timerView = new TimerView();
document.getElementById('root').append(timerView.root);
timerView.onStart(start);
timerView.onStop(stop);
timerView.onReset(reset);

function start(timerView) {
  if (!createClock) {
    createClock =...