fetch.ts

export interface Recruitment {
  id?: number;
  name: string;
  type: number;
}

export interface ApiEndpoint {
  '/v1/api/recruitments': { params: null, response: Recruitment[]};
  '/v1/api/recruitments/:id': { params: [number], response: Recruitment};
}

@Injectable()
export class RecruitmentService {
  fetch<E extends keyof ApiEndpoint>(endpoint: E, ...args: ApiEndpoint[E]['params'][]): Observable<ApiEndpoint[E]['response']> {
    return this.http.get<ApiEndpoint[E]['response']>(`${endpoint}${args}`);
  }
}

export class ListComponent implements OnInit {
  public recruitments: Recruitment[];
  public recruitment: Recruitment;
  ngOnInit() {
    const id = 1;
    this.recruitmentService.fetch('/v1/api/recruitments').subscribe((response) => this.recruitments = response);
    this.recruitmentService.fetch('/v1/api/recruitments', id).subscribe((response) => this.recruitment = response);
  }
}