cdn方式引入react

  <script crossorigin src="https://unpkg.com/react@18/umd/react.production.min.js"></script>
  <script crossorigin src="https://unpkg.com/react-dom@18/umd/react-dom.production.min.js"></script>
  <script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>