Load React in HTML template.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<h1>ReactDom in browser</h1>
<div id="app"></div>
<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<script src="my_app.js"></script>
<script>
const content = React.createElement('h2', '', 'my content');
ReactDOM.render(content, document.getElementById('app'));
</script>
</body>
</html>