I want to create a user registration with custom usernames. I store the user's username on a user document in Firestore. How can I validate a username already exists in my Users Collection?
![](https://i.stack.imgur.com/WARAs.png)
Maybe someone already have snippet for reactive form validation?
See Question&Answers more detail:
os 与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…