hanksudo/app.js

## app.js
'use strict';

function App(props) {
  return <h1>Hello, world!</h1>
}

ReactDOM.render(<App />, document.querySelector('#root'));

## index.html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="root"></div>
    <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 crossorigin src="https://unpkg.com/@babel/standalone/babel.min.js"></script>
    <script type="text/babel" src="./app.js"></script>
</body>
</html>
	'use strict';

	function App(props) {
	return <h1>Hello, world!</h1>
	}

	ReactDOM.render(<App />, document.querySelector('#root'));
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
	</head>
	<body>
	<div id="root"></div>
	<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 crossorigin src="https://unpkg.com/@babel/standalone/babel.min.js"></script>
	<script type="text/babel" src="./app.js"></script>
	</body>
	</html>