Untitled

<!DOCTYPE html>
<html>

  <head>
    <title>My website</title>
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <script src="https://unpkg.com/react@15/dist/react.js"></script>
     <script src="https://unpkg.com/react-dom@15/dist/react-dom.js"></script>
     <script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.6.16/browser.js"></script>
  </head>

  <body>
    <div id="example"></div>
    <script type="text/babel" src="index.js"></script>
  </body>

</html>

ReactDOM.render(<h1>testin</h1>, document.getElementById('example'));