const App = () => {
  const [keyDown, setKeyDown] = React.useState('');
  
  React.useEffect(() => {
    document.addEventListener('keydown', (event) => {
      setKeyDown(event.key);
    });
    return () => {
      document.removeEventListener('keydown', ()=> {
        setKeyDown('');
      });
    }
  }, []);
  return (
    <div>
      <h1>你目前按下的按鈕是：{ keyDown }</h1>
    </div>
  )
}

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