It was pretty hard to do viz on the web 13 years ago. In 2006 I made a web tool to turn regular expressions into NFAs and DFAs and animate their states as you typed. It took a lot of code (drawing and animating along beziers, AJAX to a server for graphviz and a regex compilation and minimization package I wrote for this). https://imgur.com/gallery/Yqqoh

These days there’s a lot more tooling and components that can snap together to make this kind of thing.