How to get React to update in the browser without a bundle system?

This question was asked on Kent C. Dodds Beginners Guide to React course:

Hello Kent, What are you using to make the browser dynamically reflect changes as you type - considering we’re updating a plain ‘.html’ file, and don’t have a build system like webpack running. Thanks.

I believe it is because Kent used babel stand alone in a script tag and changed the script type from text/javascript to text/babel.

<script src=""></script>
<script type="text/babel">

Kent introduces the concept in this video:

If anyone had anything to add Mahesh and I would appreciate it.