Typescript: Type X is missing the following properties from type Y length, pop, push, concat, and 26 more. [2740]

You are returning Observable<Product> and expecting it to be Product[] inside subscribe callback.

The Type returned from http.get() and getProducts() should be Observable<Product[]>

public getProducts(): Observable<Product[]> {
    return this.http.get<Product[]>(`api/products/v1/`);
}

You have forgotten to mark the getProducts return type as an array. In your getProducts it says that it will return a single product. So change it to this:

public getProducts(): Observable<Product[]> {
    return this.http.get<Product[]>(`api/products/v1/`);
  }

For those newbies like me, don't assign variable to service response, meaning do

export class ShopComponent implements OnInit {
  public productsArray: Product[];

  ngOnInit() {
      this.productService.getProducts().subscribe(res => {
        this.productsArray = res;
      });
  }
}

Instead of

export class ShopComponent implements OnInit {
    public productsArray: Product[];

    ngOnInit() {
        this.productsArray = this.productService.getProducts().subscribe();
    }
}

You must specify which type the response is:

this.productService.getProducts().subscribe(res => {
    this.productsArray = res;
});

Try this:

this.productService.getProducts().subscribe((res: Product[]) => {
    this.productsArray = res;
});

I had the same problem and I solved as follows define an interface like mine

export class Notification {
    id: number;
    heading: string;
    link: string;
}

and in nofificationService write

allNotifications: Notification[]; 
  //NotificationDetail: Notification;  
  private notificationsUrl = 'assets/data/notification.json';  // URL to web api 
  private downloadsUrl = 'assets/data/download.json';  // URL to web api 

  constructor(private httpClient: HttpClient ) { }

  getNotifications(): Observable<Notification[]> {    
       //return this.allNotifications = this.NotificationDetail.slice(0);  
     return this.httpClient.get<Notification[]>

(this.notificationsUrl).pipe(map(res => this.allNotifications = res))
      } 

and in component write

 constructor(private notificationService: NotificationService) {
   }

  ngOnInit() {
      /* get Notifications */
      this.notificationService.getNotifications().subscribe(data => this.notifications = data);
}