How to get the email of any user in Firebase based on user id?

Question

I need to get a user object, specifically the user email, I will have the user id in this format:

simplelogin:6

So I need to write a function so

Answer 1

Current solution as per latest update of Firebase framework:

firebase.auth().currentUser && firebase.auth().currentUser.email

See: https://firebase.google.com/docs/reference/js/firebase.auth.Auth.html#currentuser

Every provider haven't a defined email address, but if user authenticate with email. then it will be a possible way to achieve above solution.