Comprehending the concepts of Observables, Promises, using "this" keyword, and transferring data within Angular with TypeScript

I am trying to figure out why I keep receiving the error message:

"Uncaught (in promise): TypeError: this.dealership is undefined"

when working with the authentication.service.ts file.

export class AuthenticationService {
  private currentUserSubject: BehaviorSubject<UserModel>;
  public currentUser: Observable<UserModel>;

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

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

  login(username: string, password: string) {
    // Code for login function
  }

In the DealerSiteComponent,

export class DealerSiteComponent {
  // Code for DealerSiteComponent
}

I admit that I struggle with understanding Observables. How can I improve my knowledge in this area?

Thank you.

Answer №1

To access the core Subject from your service within your component, you must expose it first. Then, in your component, you can use subscribe on the exposed Subject to retrieve the actual value.

A helpful tip for your code is to avoid overcrowding the constructor with excessive amounts of code. It would be better to handle this functionality in the ngOnInit lifecycle hook instead.

Answer №2

Your authentication.service.ts seems to be structurally sound without any issues.

The main problem lies in the implementation of DealerSiteComponent, which is leading to the error you mentioned:

You are trying to access properties of an uninitialized variable dealership, and then assign values to those properties. Additionally, you need to subscribe to the service's login method to receive observables, which will update currentUserSubject with the response from the http request made in the login method. Finally, it would be better to move the logic present in the constructor to the ngOnInit lifecycle hook.

interface Dealership {
  dealerName?: string;
  dealerId?: string;
}

export class DealerSiteComponent implements OnInit {
  private dealership: Dealership = {
    dealerName: undefined,
    dealerId: undefined,
  }
  // continue with your code

  ngOnInit() {
    this.authService.login.subscribe(() => {
      const userDetails = this.authService.currentUserValue;
      console.log(userDetails);
      this.dealership.dealerName = localStorage.getItem('currentDealer');
       this.dealership.dealerId = localStorage.getItem('currentDealerID');
       // handle the rest of the code
    });

  }
}

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