const element = <h1>Hello World</h1>

ReactDOM.render(element, document.getElementById('root'));

  <div id="output"></div>
  <!-- Load Babel -->
  <!-- v6 <script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script> -->
  <script src="https://unpkg.com/@babel/standalone/babel.min.js"></script>
  <!-- Your custom script here -->
  <script type="text/babel">
  const getMessage = () => "Hello World";
  document.getElementById('output').innerHTML = getMessage();
  </script>