Tree-shakeable providers Example

tree-shakeable-providers.ts

// Here's a fictitious LayoutService without a module!
//
// It'll automatically be available in the application's
// root injector (as if it was provided in the AppModule).
//
// Even though it's in the root injector, if this service
// is only used in a lazy loaded context, it will be lazy
// loaded!

@Injectable({
  providedIn: 'root',
  useClass: DefaultLayoutService
})
export abstract class LayoutService {
  getLayout(element: any): Layout;
}

@Injectable()
export class DefaultLayoutService {
  ...
}

// If you still want this service to behave as if it was
// provided directly in a module, you can do that too:

@NgModule({
  providers: [
    // No provider needed - @Injectable will reference the @NgModule
    // and behave as if this provider was declared:
    // 
    // {provide: LayoutService, useClass: DefaultLayoutService}
  ]
})
export class LayoutModule {}

@Injectable({
  providedIn: LayoutModule,
  useClass: DefaultLayoutService
})
export abstract class LayoutService {...}