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

user_11549232 0
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@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?

angular typescript
4 Answers

Typescript became stricter.

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

private currentUserSubject: BehaviorSubject<User | null>;
user_110788570

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

user_48564130

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

user_34468350

Juts use it like:

this.currentUserSubject.next();

or

this.currentUserSubject = new BehaviorSubject<User | null>(JSON.parse(localStorage.getItem('currentUser')));
user_114665510
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