const App = () => {
  const ref = React.useRef(0);

  React.useEffect(() => {
    setTimeout(() => {
      ref.current += 1;
    }, 2000)
  }, []);

  return (
    <div>
      { ref.current }
    </div>
  );
}

const root = ReactDOM.createRoot(document.querySelector('#root'));
root.render(<App />);