Add proxy on Injectable

I have a AngularTS front-end, with a service SaveService

I would like to add a Proxy on it. I did not find a lot of documentation about it.
I tried naive implementation :

export class SaveService {
  private proxyService: SaveService | null = null;

  constructor(private injector: Injector) {
    const originalService = this.injector.get(SaveService);
    const proxyService = new Proxy<SaveService>(originalService, {
      get: (target, prop: keyof SaveService, receiver) => {
        console.log(`Calling method: ${prop}`);
        return target[prop];
      },
    });

  }
}

But it cannot works like this because this.injector.get(SaveService) is a Circular dependency

Any ways to add a proxy on this injectable service ?

I think I understand what you mean by using proxy, but in Angular world this would be called an Interceptor. Its job is to intercept the requests and do some stuff with them, usually to append some headers or do logging.

@Injectable()
export class InterceptorService implements HttpInterceptor {
  public intercept(
    req: HttpRequest<any>,
    next: HttpHandler
  ): Observable<HttpEvent<any>> {
    console.log('REQUEST:', req),
    return next.handle(req).pipe(
      tap((res: HttpResponse<any>) => console.log('RESPONSE:)', res),
    );
  }
}

In your case, it might look like this:

@Injectable()
export class InterceptorService implements HttpInterceptor {
  // Let's pretend that's how your auth service is called
  constructor(private firebaseService: FirebaseService)

  public intercept(
    req: HttpRequest<any>,
    next: HttpHandler
  ): Observable<HttpEvent<any>> {
    // Check if user is authenticated
    if (firebaseService.isAuthenticated()) {
      // if so, continue
      return next.handle(req);
    } else {
      // If not, authenticate and contine
      return firebaseService.authenticate().pipe(
        map(() => next.handle(req))
      )
    );
  }
}

So your interceptor check if user is logged in and if not, it'll call the authenticate method and when it's successful it continues with original request. You can also add AUTH headers and so on... But take this code as an example and adjust it to your own needs.