[pocket_titan]

I'd suggest just learning and applying fp principles in JS incrementally. You'll feel a bit constrained at first (in part b/c JS allows you to do many "dirty" things), but you'll end up writing better code. Try to rely on 1) pure functions/no side-effects: a functions return value should be completely determined by its input 2) immutability: no Array.push, pop, or any method that modifies its input values 3) recursion instead of for & while loops.

You'll probably feel the need for stronger typing at some point when adhering to these principles, and that's when I'd suggest looking at Typescript. By trying the things above you'll likely get familiar with the issues TS is trying to solve & you'll appreciate it more. Note that fp-ts is just a "helper" library for functional concepts, but it won't teach you their value or how to use them.

Also: many libraries have fp variations! Next time you reach for lodash, try lodash/fp instead: it has the same tools you'll already be familiar with, but implemented in a functional manner.