An Introduction to Observables for Ionic 2

An Introduction to Observables for Ionic 2

Follow Josh Morony on

Observables are one of those new tricky things you will almost certainly run into at some point when building an application with Ionic 2. They can seem a little weird and overwhelming at first, and you might wonder ”why can’t we just stick to promises?”, but they are quite beautifully implemented. At a basic level, you don’t need to worry about all of the advanced things observables can do or what “reactive programming” is, you will mostly just need to know a few basics like how to subscribe to an observable.

In this video tutorial, I cover the basic concept of observables and how they are relevant to an Ionic 2 application.

Here’s the video:

Video Notes

  • Observables are provided by the RxJS library – they are not specific to Ionic or Angular
  • Observables are somewhat similar to promises, but they can do a lot more
  • Observables can emit multiple values over time, rather than just resolving once
  • You can subscribe to an observable to do things with the data that it emits
  • Observables are “lazy” meaning that they won’t be executed until they are subscribed to
  • Multiple different operations can be applied to observables to modify the observable and return a new one
  • The first observables you will likely run into when building Ionic 2 applications is through the Http service, or through an Ionic Native plugin
  • You can create your own observables, but at a beginner level this will not likely ever be necessary
  • You can create your own observable using the following format:
let myObservable = Observable.create(observer => {
	observer.next("hello");
});

myObservable.subscribe((data) => {
	console.log(data);
});
  • A Subject combines the observer/observable pattern into one easy to use method, which you may prefer to use for simple implementations
  • You can create a Subject with the following code:
let mySubject = new Subject();

        mySubject.subscribe((data) => {
            console.log(data);
        });

        mySubject.next("hello");
Check out my latest videos: