Reactive Programming Basics

RxJs-Observables.md

RxJS

Creating Observables

The create operator in the Rx.Observable object takes a callback that accepts an Observer as a parameter. That function defines how the Observable will emit values

var observable = Rx.Observable.create(function(observer) { 
	observer.onNext('Sergio');
   observer.onNext('Tyrone');
   observer.onNext('Choiman');
   observer.onCompleted(); // We are done 
});

Observers listen to Observables

Whenever an event happens in an Observable, it calls the related method in all of its Observers

Observers have three methods:

• onNext The equivalent of Update in the Observer pattern. It is called when the Observable emits a new value. Notice how the name reflects the fact that we’re subscribed to sequences, not only to discrete values.

• onCompleted Signals that there is no more data available. After onCompleted is called, further calls to onNext will have no effect.

• onError Called when an error occurs in the Observable. After it is called, further calls to onNext will have no effect.

Creating Observers

The create method in the Rx.Observer object takes functions for the onNext, onCompleted, and onError cases and returns an Observer instance. These three functions are optional, and you can decide which ones to include.

var observer = Rx.Observer.create(function onNext(x) { 
	  console.log('Next: ' + x); 
	}, function onError(err) { 
	  console.log('Error: ' + err); 
	}, function onCompleted() { 
	  console.log('Completed'); 
});