To use React js directly in HTML just use the script of React js through React js CDN
How to use React js script CDN directly in HTML ?
to use React js CDN directly in HTML just write React js CND script in head tag of HTML
<html>
<head>
<script src="https://unpkg.com/react@16/umd/react.production.min.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js"></script>
<script src="https://unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>
</head>
</html>