[risto1]

My 2 cents: I love functional programming, but sometimes imperative code is the right solution for something, like quicksort.

I'm ok with imperative code as long as the mutable state doesn't 'leak out' into the rest of the code. Quicksort is an example of that -- it's impure in it's implementation but essentially pure to the end user, because you can call it any number of times with the same input and it'll always return the same output

Or if it's some looping construct, recursion might be ok but if it isn't readable or you don't get tail-call optimization, then a for or while loop makes more sense. I do prefer map/filter/reduce/forEach or recursion, I think it's more readable and it avoids the indexing class of errors