Great points! I am still trying to figure out how to best use functional programming with JavaScript. I've found writing performance critical parts imperatively while being conscious about shared mutable state is a decent compromise.

> My second advice is to not use recursion to process arrays languages (like JavaScript) that have a very limited call stack size.

Can also confirm this, here was my process on the some of the harder days in Advent of Code:

1. I wonder if I can solve this in a pure functional style with JavaScript

2. Yay, it works on the example input

3. Oh, I hit the call stack limit on the real input

4. Time to rewrite the recursion as a loop lol