scaffold expense list

src/app/services/category.service.ts

@@ -0,0 +1,20 @@
+import { Injectable } from '@angular/core';
+import { HttpService } from './http.service';
+
+@Injectable({
+  providedIn: 'root',
+})
+export class CategoryService {
+  public static readonly CATEGORY_PATH = 'http://localhost:3000/common-cents/categories';
+
+  public constructor(private readonly http: HttpService) { }
+
+  public async getCategories(): Promise<Category[]> {
+    return this.http.get<Category[]>(CategoryService.CATEGORY_PATH);
+  }
+}
+
+export interface Category {
+  id: string;
+  name: string;
+}