Cool. I have been working through the lessons in Nathan's University (http://nathansuniversity.com/) which take you writing a Lisp interpreter (though admittedly with less rigor than this project) in Javascript.
Definitely recommended if you want a starting point for something similar and don't know where to begin.
For anyone interested in the detail of _how_ to create a game engine from scratch, I'd recommend checking out Handmade Hero https://handmadehero.org/