Don't push, concat

This is something I always knew, but for some reason, I keep on forgetting, hopefully writting about it will help it sink in.

JavaScript arrays (among others) have two distinct ways of adding items, we can either .push or .concat. The former will actually modify the original array by adding the new item to it, the latter will create a completely new array that is a copy of the original with the new item added to the end.

So, we all know that immutability is not only a desire, it's a necessity, using .concat will take us one step closer to JS bliss.