ASP.NET Core and Angular 2 by 2016

Author:2016
Language: eng
Format: epub
Publisher: Packt Publishing

With these additions, our GUI should be ready; before going further, let's perform a full surface test.

Note

While we don't want to talk too much about Angular 2 and its http class, we should definitely spend a few words talking about its new abstraction pattern based upon observables.

One of the most relevant differences with the previous approach is that observables have a lazy behavior by design, meaning that they won't fire unless there is a valid subscription issued by a .subscribe() function call. This is a major perspective switch from the AngularJS Promises, which would execute right off the bat regardless of how the client code will use their result afterward.

Another important difference involves the .subscribe() function, which will be fired upon completion of the ItemService's add task. In Angular 2, subscriptions are designed to work just like a standard .then() or .complete() function featured in most async-based JavaScript libraries (AngularJS/Promises, JQuery/AJAX, and more), with the key difference that they are also bound to the Observable itself; this means that they won't just trigger once and resolve, but they will be executed each and every time the Observable completes its task(s) until it ceases to exist, unless they get cancelled by calling the .unsubscribe() function method on their Observable.

That said, we can easily notice that these HTTP requests are hardly a good example to demonstrate the advantages of this behavior, as these are observables that will fire only once; we'll see it better when we implement some reactive functionalities such as search with autocomplete and similar stuff.

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