A guide to utilizing NGXS Select() within an Angular component

A recent project of mine involves using NGXS in an Angular setup.

Within my AuthState, I have the following code snippet:

@Injectable()
export class AuthState {
  @Selector()
  static isAuthenticated(state: AuthStateModel) {
    return state.currentUser !== null;
  }
  //...
}

When implementing this in a component, I encountered an issue:

export class HeaderComponent implements OnInit {
  @Select(AuthState.isAuthenticated) isAuthenticated$: Observable<boolean>;
  //...
}

Unfortunately, this resulted in a compilation error:

src/app/layout/header/header.component.ts:14:38 - error TS2564: Property 'isAuthenticated$' has no initializer and is not definitely assigned in the constructor.

14   @Select(AuthState.isAuthenticated) isAuthenticated$: Observable<boolean>;
                                        ~~~~~~~~~~~~~~~~

I understand why Angular is facing this problem, as it cannot ensure proper initialization upfront.

After researching a bit, I came across suggestions to disable property initialization checks by adding the following line to the tsconfig file:

"strictPropertyInitialization": false

However, I prefer to keep this check enabled for better development practices. Is there a way to address this issue without disabling it application-wide while still utilizing NGXS Select feature?

Answer №1

If you're certain that you do not wish to initialize your property, you have the option to utilize TypeScript's non-null assertion operator (!) preceding the type of your property:

export class HeaderComponent implements OnInit {

  @Select(AuthState.isAuthenticated) isAuthenticated$!:Observable<boolean>;
  //...

}

This will resolve any compilation errors. Think of this operator as a way to communicate with TypeScript: "I guarantee this property won't be undefined, so please don't give me a hard time :D"

By using it, you can maintain your decorator instead of moving the initialization logic to the constructor, and you can also uphold your "strictPropertyInitialization" setting.

Answer №2

If you prefer not to modify the setting, then you can establish it through the constructor.

constructor(dataStore: Store){
    this.isLoggedIn$= dataStore.select(AuthenticationState.isLoggedIn);
}

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