core.module.ts

@NgModule({
  declarations: [],
  imports: [CommonModule],
  providers: [
    {
      provide: APP_INITIALIZER,
      useFactory: appInitializer,
      multi: true,
      deps: [AuthService],
    },
    { provide: HTTP_INTERCEPTORS, useClass: JwtInterceptor, multi: true },
    {
      provide: HTTP_INTERCEPTORS,
      useClass: UnauthorizedInterceptor,
      multi: true,
    },
  ],
})
export class CoreModule {
  constructor(@Optional() @SkipSelf() core: CoreModule) {
    if (core) {
      throw new Error('Core Module can only be imported to AppModule.');
    }
  }
}