W3Schools Tryit Editor

main.jsx

index.html

import { useState, useEffect } from 'react';
import { createRoot } from 'react-dom/client';

function Timer() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    let timer = setTimeout(() => {
      setCount((count) => count + 1);
    }, 1000);

    return () => clearTimeout(timer)
  }, []);

  return <h1>I've rendered {count} times!</h1>;
}

createRoot(document.getElementById('root')).render(
  <Timer />
);

<!doctype html>
<html lang="en">
  <body>
    <div id="root"></div>
    <script type="module" src="/src/main.jsx"></script>
  </body>
</html>