const App = () => {
  const handler = (event) => {
    window.alert(`你選擇了：${event.target.value}`);
  }

  return (
    <div>
      <select onChange={ handler } name="location">
      　<option value="Taipei">台北</option>
      　<option value="Taoyuan">桃園</option>
      　<option value="Hsinchu">新竹</option>
      </select>
    </div>
  )
}

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