如何将REST数据返回给observable，然后在APP_INITIALIZER上应用逻辑？[Angular 12]

npm install @angular/common@12.0.0

import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable()
export class DataService {
  constructor(private http: HttpClient) {}

  getData(): Observable<any> {
    return this.http.get('https://api.example.com/data');
  }
}

import { APP_INITIALIZER } from '@angular/core';
import { DataService } from './data.service';

export function initializeApp(dataService: DataService) {
  return () => dataService.getData().toPromise();
}

import { NgModule, APP_INITIALIZER } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';
import { DataService } from './data.service';
import { initializeApp } from './app.initializer';

@NgModule({
  imports: [HttpClientModule],
  providers: [
    DataService,
    {
      provide: APP_INITIALIZER,
      useFactory: initializeApp,
      deps: [DataService],
      multi: true
    }
  ]
})
export class AppModule { }