Array.contains in Firestore rules

Question

How to use the JS native array.contains in Firestore rules?

function isCool() {
  return [
    'xxx',
    'yyy',
  ].contains(req.auth.uid)
}

The function above gives an error

Answer 1

You are looking for in operator:

function isCool() {
  return request.auth.uid in ['xxx', 'yyy'];
}

It returns true if the value is present in the given list/array.