react - use state

useState.jsx

const HelloWorld = () => {
  const [show, setShow] = useState(false);

  return (
    <section>
      <h1>Merhaba dünya!</h1>
      {show ? <p>Günaydın.</p> : null}
      <button onClick={() => setShow(!show)}>Merhaba!</button>
    </section>
  );
};

ReactDOM.render(HelloWorld, document.getElementById('root'));