Regex to test for lowercase characters

Regular expressions. So powerful, but so tricky to learn!

Recently I found myself scratching my head over how to write a regular expression to check that a string contained only lowercase characters.

I used so many different combinations of[a-z], ^\W, [0–9], [a-z]^\W and more. No dice. I couldn’t figure out the correct combination. Finally I thought: oh, so simple, I’ll just do the inverse! So I did the following:

const isLowercaseOnly = (string) => {
  const nonLowercaseLetters = /[^a-z]/g;
  return !nonLowercaseLetters.test(string);
};

This works, but now I have to deal with inverse. A bit confusing.

Luckily, I was working with…