Strongly Typing the Code

import { Injectable } from '@angular/core';
import { InMemoryDbService } from 'angular-in-memory-web-api';
import { Product } from './app.interfaces';
@Injectable({
  providedIn: 'root',
})
export class DataService implements InMemoryDbService {
  constructor() {}
  createDb() {
    // Replacing "any" with "Product[]"
    let products: Product[] = [
      {
        id: 1,
        title: 'The Angular Masterclass',
        author: 'Educative',
        description: 'Learn all about Angular',
        imgUrl: '../assets/img/the-angular-masterclass.jpg',
        quantity: 124,
        price: 24.38,
        cart: 0,
      },
      {
        id: 2,
        title: 'The Ultimate Guide to Redux',
        author: 'Educative',
        description: 'Learn about Redux',
        imgUrl: '../assets/img/the-ultimate-guide-to-redux.jpg',
        quantity: 524,
        price: 22.38,
        cart: 0,
      },
      {
        id: 3,
        title: 'Developing Mobile Apps with Ionic and Angular',
        author: 'Educative',
        description: 'Learn how to build mobile apps with Ionic and Angular',
        imgUrl:
          '../assets/img/developing-mobile-apps-with-ionic-and-angular.jpg',
        quantity: 146,
        price: 38.99,
        cart: 0,
      },
      {
        id: 4,
        title: 'Angular: Designing and Architecting Web Applications',
        author: 'Educative',
        description: 'Design and architect your web applications using Angular',
        imgUrl:
          '../assets/img/angular-designing-and-architecting-web-applications.jpg',
        quantity: 500,
        price: 11.98,
        cart: 0,
      },
      {
        id: 5,
        title: 'Developing Robust Angular Applications with AuthO and MongoDB',
        author: 'Educative',
        description:
          'Implement authentication using Angular, AuthO and MongoDB',
        imgUrl:
          '../assets/img/developing-robust-angular-applications-with-auth0-and-mongodb.jpg',
        quantity: 453,
        price: 30.18,
        cart: 0,
      },
      {
        id: 6,
        title: 'Full Reactive Stack with Spring Boot 2 and Spring WebFlux',
        author: 'Educative',
        description: 'Learn about Spring Boot 2 and Spring WebFlux',
        imgUrl:
          '../assets/img/full-reactive-stack-with-spring-boot-2-and-spring-webflux.jpg',
        quantity: 124,
        price: 37.18,
        cart: 0,
      },
    ];
    let shoppingCart: Product[] = [];
    return { products, shoppingCart };
  }
}

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { catchError, Observable, throwError } from 'rxjs';
import { Product } from './app.interfaces';
@Injectable({
  providedIn: 'root',
})
export class ProductsService {
  private BASE_URL: string = `api`;
  private PRODUCT_URL: string = 'api/products';
  private SHOPPING_CART_URL: string = 'api/shoppingCart';
  constructor(private httpClient: HttpClient) {}
  public getProducts(): Observable<Product[]> {
    return this.httpClient
      .get<Product[]>(this.PRODUCT_URL)
      .pipe(catchError(this.errorHandler));
  }
  public getProduct(productId: number): Observable<Product> {
    return this.httpClient
      .get<Product>(`${this.PRODUCT_URL}/${productId}`)
      .pipe(catchError(this.errorHandler));
  }
  public getShoppingCart(): Observable<Product[]> {
    return this.httpClient
      .get<Product[]>(this.SHOPPING_CART_URL)
      .pipe(catchError(this.errorHandler));
  }
  public addToShoppingCart(product: Product) {
    const headers = {
      headers: new HttpHeaders({ 'Content-Type': 'application/json' }),
    };
    return this.httpClient
      .post<Product>(`${this.BASE_URL}/shoppingCart`, product, headers)
      .pipe(catchError(this.errorHandler));
  }
  private errorHandler(err: any) {
    let errMsg: string;
    if (err.error instanceof ErrorEvent) {
      errMsg = `Frontend Error: ${err.error.message}`;
    } else {
      errMsg = `Backend Error Code: ${err.status}: ${err.body.error}`;
    }
    return throwError(errMsg);
  }
}