CODEWITHSUNDEEP
angularobservablengrxsubscriptionngrx-store
user3261695
user3261695

Reputation: 27

why the Ngrx selector fires without subscription?

my question center around this peace of code

@Injectable()
export class TokenInterceptor implements HttpInterceptor {
constructor(private store: Store<fromAuth.State>) {}

intercept(req: HttpRequest<any>, next: HttpHandler) {
  return this.store.select(fromAuth.getToken).pipe(
   first(),
   flatMap(token => {
    const authReq = !!token ? req.clone({
      setHeaders: { Authorization: 'Bearer ' + token },
    }) : req;
    return next.handle(authReq);
   },
  );
 }
}

i didn't understant the need of the operator first(), the author gave that explanation

The observable that we return from the intercept method begins with the store selector. Since this 
observable will form part of the chain when creating a new HttpClient request and subscribing, we 
don’t want to send an update everytime the token changes in the future, else the services using 
HttpClient will appear to get a new value from their request if not unsubscribed. Thus we use the 
first() operator here to only take the first value, then complete

the select selector returns an observable and is supposed to fires every time the state changes in the store, but where is the subscription to the observable returned by select

link to the originale article : https://antonyderham.me/post/angular-ngrx-auth-interceptor/

Upvotes: 1

Views: 223

Answers (1)

satanTime
satanTime

Reputation: 13539

it's internal implementation of the interceptor handler. It subscribes to result of intercept method and uses an emitted value to send a request.

it looks similar to 

const interceptor = new TokenInterceptor(store);
interceptor.intercept(new HttpRequest('POST', '/test', {}), backend).subscribe();

but it's under the hood of angular.

Upvotes: 1

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