HTTP

The categories are currently hardcoded values; however, they should be loaded from the RESTful API and through HTTP calls. Angular provides its own abstraction for HTTP, in the form of a service that you can use when necessary.

Next, let's use Angular's HttpClient service to load the categories from the backend RESTful API:

1. Import HttpClientModule into app.module.ts to make the HttpClient service available to the entire app:

…
import { HttpClientModule } from '@angular/common/http';
…
@NgModule({
  …
  imports: [
    HttpClientModule,
    …
  ],
  …
})

2. Use the HttpClient service in CategoriesService as follows. If the HTTP address differs in your setup, then make sure to change it accordingly:

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { CoreModule } from '../core.module';
import { Category } from '../../../model';

@Injectable({
  providedIn: CoreModule,
})
export class CategoriesService {
  constructor(private readonly http: HttpClient...