Dependency Injection in Angular

                    @Injectable({providedIn: 'root'})
                    export class Service {..}
                

@Injectable({
  providedIn: 'root',
  useFactory: () => new MusicService('dependency'),
})
                

                    [{ provide: Logger, useClass: TimestampedLogger }],
                    [Logger]

                    [{ provide: Logger, useClass: TimestampedLogger },
                     { provide: BasicLogger, useExisting: Logger}]

export function SilentLoggerFn() {}
const silentLogger = {
  logs: ['Silent logger says "Shhhhh!". Provided via "useValue"'],
  log: SilentLoggerFn
};
[{ provide: Logger, useValue: silentLogger }]

                    [{ provide: MusicService,
                      useFactory: musicServiceFactory,
                      deps: [Logger, UserService]}]