A lot of that stuff is pretty modern in terms of FP, though. It's definitely not a pure functional language, though quite a lot of the data is actually immutable. It was really surprising to me that strings are immutable (but as the other commenter pointed out, they don't throw if you try to mutate them, so it's not that convenient). "Objects" and arrays are mutable, but it's pretty easy to avoid mutating them if you want to.

It probably wasn't clear, but the reason I didn't use any dependencies is because I was avoiding JS's built in inheritance mechanism, which I don't think is very compatible with FP. You can build objects out of closures and build your own object oriented mechanisms if you want. Unfortunately you run into the limitations of the implementations I mentioned.

I always hesitate to link to my own "fun" code, but just so you understand that I was not looking for code quality in this: https://gitlab.com/mikekchar/testy But it shows how I was using an FP style in JS to implement an alternative OO system. I really had fun writing this code and would have continued if there weren't problems with using closures in JS.

Edit: If you look at this, it's probably best to start here: https://gitlab.com/mikekchar/testy/blob/master/design.md

I really should link that in the README...