Return an @angular/fire User as a Promise

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@angular/fire provides an authState Observable which is great for reacting to realtime changes to the user’s login state. However, it can be useful to also return this value as a Promise for one-off operations and for use with async/await.

Let’s say we have an auth service using Firebase. We can take the first() emitted value from the stream, then convert it using toPromise();

file_type_ng_component_ts app/auth.service.ts 
import { Injectable } from '@angular/core';
import { AngularFireAuth } from '@angular/fire/auth';

import { first } from 'rxjs/operators';

@Injectable({ providedIn: 'root' })
export class AuthService {

    constructor(private afAuth: AngularFireAuth) { }

    getUser(): Promise<any> {
        return this.afAuth.authState.pipe(first()).toPromise();
    }

}

Usage with Async/Await in a Guard

Now we can use this method throughout the app for tasks that do not require a stream, like database writes or in router guards as shown below:

file_type_ng_component_ts app/auth.guard.ts 
import { Injectable } from '@angular/core';
import { CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot } from '@angular/router';
import { AuthService} from './auth.service'

@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private auth: AuthService) {}

  async canActivate(...): Promise<boolean> {

      const user = await this.auth.getUser();
      const loggedIn = !!user;

      if (!loggedIn) {
          // do something
      }

      return loggedIn;
  }
}

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