In that case I'd argue use lodash: https://lodash.com/docs/4.17.15#isNumber https://lodash.com/docs/4.17.15#isNumber It's well respected, battle tested, and yo

In that case I'd argue use lodash: https://lodash.com/docs/4.17.15#isNumber https://lodash.com/docs/4.17.15#isNumber It's well respected, battle tested, and you can just pull in the functions you actually use. It doesn't have isEven, but it probably drew a good line there.