RXJS - Check data before subscribe

I want to implement a generic HTTP helper for an Angular project. The backend retuns all Get responses with this schema :

{
 data: any[]; // response data 
 status:string; // response status , [ ok , problem ]
 message:string; // error message
}

I implemented the generic get helper as follow

get<T>(endPoint): Observable<T> {
   this.notifier.notify('info', 'Loading ...');
     return this.http.get(endPoint).pipe(
          map((o) => o.data),
                catchError((err) => {
                    this.notifier.notify('error', err);
                    return throwError(err);
                })
   ) as Observable<T>;
}

The HTTP errors will catch by catchError, so the notifier service will show the error.

For custom errors, I don't know how to catch them in this code and show the error (if statusisproblem`, also I don't want to handle this error after subscribing).

Solution 1:

You could use tap which is used for handling side effects actions, in this case, for handling the response's status if it is a problem:

  get<T>(endPoint: string): Observable<T> {
    this.notifier.notify('info', 'Loading ...');
      
    return this.http.get(endPoint)
    .pipe(
        tap((response) => {
          if (response.status === 'problem') {
            // do something with it
          }
        }),
        map((o) => o.data),
        catchError((err) => {
          this.notifier.notify('error', err);
          return throwError(err);
        })
    ); // no need of .asObservable<T>, any http calls return an observable
       // if you hover over your get function, you will see that the return
       // type is already Observable<T>
 }
}

Solution 2:

this should work:

get<T>(endPoint): Observable <T> {
  this.notifier.notify('info', 'Loading ...');
  return this.http.get(endPoint).pipe(
    map(o => {
      if (o.status !== 'ok') {
        throw 'problem in request status';
      }
      return o.data;
    }),
    catchError((err) => {
      this.notifier.notify('error', err);
      return throwError(err);
    })
  ) as Observable<T>;
}