nastyService.ts

@Injectable()
export class NastyService {
  constructor() {
  }

  doNastyOperation(key: any) {
    switch (key) {
      case 1:
      // logic
      case 2:
      // logic
      case 3:
      // logic
      case 4:
      // logic
      default:
      // logic
    }
  }
}