Comment by ShellfishMeme

JS does not have an Integer type, so (x > 0) does not work. Now if you add all those checks necessary to see whether you're actually dealing with an integer here, you get to a point where you cannot be sure anymore whether there aren't any weird type coercion issues there and need to start writing tests. Suddenly your whole positive integer check took 1h to write and you still cannot be sure whether there's something you didn't think of. I'd rather use an external library for that that's properly unit tested.