TransferHttpCacheModule不会阻止Angular 8中的重复HTTP调用

Question

我已经用Angular Universal设置了Angular 8项目。为了防止重复的HTTP调用，Angular提供了 TransferHttpCacheModule 。

我遵循官方文档将 TransferHttpCacheModule 添加到Angular（https://github.com/angular/universal/blob/master/docs/transfer-http.md）

我还尝试添加 BrowserTransferStateModule （https://www.twilio.com/blog/faster-javascript-web-apps-angular-universal-transferstate-api-watchdog），但这也不起作用。

app.module.ts

import {BrowserModule} from '@angular/platform-browser';
import {AppRoutingModule} from './app-routing.module';
import {AppComponent} from './app.component';
import {TransferHttpCacheModule} from "@nguniversal/common";

@NgModule({
  declarations: [
    AppComponent,
    ...
  ],
  imports: [
    BrowserModule.withServerTransition({appId: 'serverApp'}),
    TransferHttpCacheModule, // <-
    ...
    HttpClientModule
  ]
  bootstrap: [AppComponent]
})
export class AppModule {
}

app.server.module.ts

import {NgModule} from '@angular/core';
import {ServerModule, ServerTransferStateModule} from '@angular/platform-server';

import {AppModule} from './app.module';
import {AppComponent} from './app.component';
import {ModuleMapLoaderModule} from '@nguniversal/module-map-ngfactory-loader';

@NgModule({
  imports: [
    AppModule,
    ServerModule,
    ModuleMapLoaderModule,
    ServerTransferStateModule // <-
  ],
  bootstrap: [AppComponent],
})
export class AppServerModule {
}

main.ts

document.addEventListener('DOMContentLoaded', () => {
  platformBrowserDynamic()
    .bootstrapModule(AppModule)
  .catch(err => console.error(err));
});

我的Api服务 api.service.ts

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

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

  private API_URL = '/api/';

  constructor(private http: HttpClient) {
  }

  public get<T>(url: string): Observable<T> {
    return this.http.get<T>(this.API_URL + url);
  }

  public post<T>(url: string, payload: T): Observable<T> {
    return this.http.post<T>(this.API_URL + url, payload);
  }

  ...

}

HTTP调用 home.component.ts

import {Component, OnInit} from '@angular/core';
import {ApiService} from "../../api.service";
import {Offer} from "../../offer-preview/offer.model";

@Component({
  selector: 'app-home',
  templateUrl: './home.component.html',
  styleUrls: ['./home.component.sass']
})
export class HomeOffersComponent implements OnInit {
  latestOffers: Offer[];

  constructor(private apiService: ApiService) {
  }

  ngOnInit() {
    this.apiService.get<Offer[]>("offer")
      .subscribe(data => this.latestOffers = data);
  }

}

根据正式的TransferHttpCacheModule文档，浏览器不应将XHR制作为 / api / offer ，但我会在开发人员网络工具中看到XHR调用。

我在做什么错？我有想念吗？