const App = () => {
  const [myName, setMyName] = React.useState('Ray');
  
  return (
    <div>
      { myName }
      <button type="button" onClick={ () => setMyName('QQ 先生') }>更改名字</button>
    </div>
  )
}

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