Subscribe to multiple Observables (like chaining then() in Promises)

Question

My Angular 2 application has 2 methods (GetCategories() and GetCartItems()) in a service , and both of these methods return Observable

Answer 1

Looks like GetCartItems doens't depend on GetCategories. Then you can use zip:

Observable
    .zip(
        this.appService.GetCategories()
        this.appService.GetCartItems()
    )
    .catch(err => this.toaster.error(err))
    .subscribe(([categories, cartItems]) => {
        this.appService.categories = categories;
        this.appService.cart = cartItems;
    });