Anyone who needs to test an input is an odd number using vanilla JS will eventually end up rolling something that looks a lot like isOdd() themselves (or they'll just ignore a set of potential problems, which definitely is worse). It's very obvious when you read the code - https://github.com/jonschlinkert/is-odd/blob/master/index.js.

Utilities like that are a function of using a weakly typed language. "Just use TypeScript" is an alternative solution, but even in TS you should still check the number is within the bounds of isSafeInteger.