index-01c

HTML

<!DOCTYPE html>
<html lang="en">

  <head>
    <meta charset="UTF-8">
    <title>React</title>
  </head>

  <body>
    <div id="root"></div>
    <script src='//unpkg.com/react/umd/react.development.js'></script>
    <script src='//unpkg.com/react-dom/umd/react-dom.development.js'></script>
    <script src="//unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>
  </body>

</html>

Babel + JSX

ReactDOM.render( < h1 > Hello, world! < /h1>,document.getElementById('root'));