I solved it this way, knowing that it was probs going to be the top solution (since the top answer is typically the most clever/clean answer, not always the most efficient). That being said, I've never flip-flopped my oppinion about my answer so many times while reading a discorse on codewars before... lol. It's 8kyu and we're all overthinking the crap out of it.

I would say this is best practice since it is easier to read and understand.

The if solution is more likely to be written wrong or get misunderstood.

You've spent more time writing that than we've thought about the problem.

Performance is a mechanic to consider for your task, and in this context when our goal is to solve a self contained problem with implied constraints, if it's fast enough to pass the test cases, it's the best practice.

You can argue about O(1) vs O(2) all you want, but quite honestly it's javascript we're talking about here and the engine is better at running fast code than you are at writing fast code. Go use C++ or something.

No problem, I revisited my first solution and it mutated the input too ;). Refactored it to make it pure now.