Who even uses is-odd and is-even?

They're used because of the nonsense that was JS' beginning, in that you couldn't use integers safely past 2^53 - 1 due to floating point limitations.

Limitations that were because of JS chose to only support one primitive data type for numbers, and that was only recently resolved with the introduction of BigInt & BigInt literals. In 2018.

I'd imagine people that learned to code at a crappy bootcamp where they were told to just find npm packages for whatever they're trying to do because they're better/safer/faster.

HN uses this once per year on Cristmas, colouring numbers of the posts with red&green.