I've always liked Learn you a Haskell, but it's a trip to get through and you may need to re-read it a few times for things to stick. Another helpful one is Fu

I've always liked Learn you a Haskell, but it's a trip to get through and you may need to re-read it a few times for things to stick. Another helpful one is Functional Javascript. It showed me a new, better, way to write my JS code. I found it can be easier on your mind when you pick it up almost like vim. First you learn how to move around with hjkl (perhaps a functional equivalent is using .map() and .filter() instead of for loops), then you navigate by lexical concepts with w, e, $, %, etc (maybe using .zip()), then build macros with @ (currying), etc. Each step you learn and use regularly helps when stretching your brain to pick up more. You definitely don't need to rewrite everything in a functional way to take advantage of it.