Argument of type 'null' is not assignable to parameter Angular

Question

@Injectable({ providedIn: 'root' })
export class AuthenticationService {
    private currentUserSubject: BehaviorSubject<User>;
    public currentUser: Observable<User>;

    constructor(private http: HttpClient) {
        this.currentUserSubject = new BehaviorSubject<User>(JSON.parse(localStorage.getItem('currentUser')));
        this.currentUser = this.currentUserSubject.asObservable();
    }

    public get currentUserValue(): User {
        return this.currentUserSubject.value;
    }

    login(username: string, password: string) {
        return this.http.post<any>(`${environment.apiUrl}/users/authenticate`, { username, password })
            .pipe(map(user => {
                // store user details and jwt token in local storage to keep user logged in between page refreshes
                localStorage.setItem('currentUser', JSON.stringify(user));
                this.currentUserSubject.next(user);
                return user;
            }));
    }

    logout() {
        // remove user from local storage to log user out
        localStorage.removeItem('currentUser');
        this.currentUserSubject.next(null);
    }
}

Any idea why am i getting error at the last line(this.currentUserSubject.next(null))? Error message: Argument of type 'null' is not assignable to parameter of type 'User'. The latest typescript version does not allow this? What would be another solution?

Gaël J · Accepted Answer · 2021-09-04 15:13:04Z

7

Typescript became stricter.

You can either turn off strict mode or make your observable accept nulls:

private currentUserSubject: BehaviorSubject<User | null>;

edited Sep 4, 2021 at 15:13

Gaël J

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answered Apr 9, 2021 at 17:48

Andrei

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3 Comments

Szocs Arnold Over a year ago

How can I turn off the strict?

Andrei Over a year ago

find strictNullChecks in tsconfig and set it to false

Gaël J Over a year ago

Don't turn off strict mode, it's here for a reason: save you from errors at runtime!

sanjeevRm · Accepted Answer · 2021-04-09 17:42:01Z

1

check if this.currentUserSubject.next(null); is really required

answered Apr 9, 2021 at 17:42

sanjeevRm

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Comments

Dharman · Accepted Answer · 2021-08-28 03:00:10Z

1

the best practice is you use always <User| null>

example private currentUserSource = new ReplaySubject<User | null>(1);

then you can call that function in this.currentUserSource.next(null); or the easiest is

private currentUserSource = new ReplaySubject(1);

then this.currentUserSource.next(); () can consider as null

edited Aug 28, 2021 at 3:00

Dharman♦

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answered Aug 28, 2021 at 2:54

Milestone89

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Comments

Zach · Accepted Answer · 2021-04-09 18:01:37Z

0

Juts use it like:

this.currentUserSubject.next();

or

this.currentUserSubject = new BehaviorSubject<User | null>(JSON.parse(localStorage.getItem('currentUser')));

answered Apr 9, 2021 at 18:01

Zach

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