How to generate a unique user id for my users?

I want to generate a unique user id for my users with the combination on a user name and some random string, something likename: 'john macco' userId: 'OA92C3' It should be short as 4 - 8 characters to able to users to remember there userId, This why I can't use the MongoDB document id as my userId.​the generator should start from 4 characters combination if whole the combination has taken by users then it should begin with 5 characters and so onI don't wanna waste your time explaining why I need this : ) TL;DR​Hope I have explained well,Thank You

Submitted June 22, 2020 at 05:21AM by Chawki_