It's kind of insane how bad this whole is-number thing is. It's designed to tell you if a string is numeric, but I would argue if you're ever using that you have a fundamental design problem. I hate dynamic typing as much as anyone else, but if forced to use it I would at least try to have some resemblance of sanity by just normalizing it to an actual number first.

Just fucking do this...

const toRegexRange = (minStr, maxStr, options) => {
  const min = parseInt(minStr, 10);
  const max = parseInt(maxStr, 10);
  if (isNaN(min) || isNaN(max)) throw Error("bad input or whatever");
  // ...

Because of the insanity of keeping them strings and only attempting to validate them (poorly) up front you open yourself up to a suite of bugs. For example, it took me all of 5 minutes to find this bug:

toRegexRange('+1', '+2')
// returns "(?:+1|+2)" which is not valid regexp