The Observable Object

The Observable object

When an Observable object is created, we register an Observer object with the Observable. Then, as the Observable receives items, it calls all its subscribed Observer’s methods. There are three handler methods that the Observable can call:

The next( ) handler

The next() method sends a value to an Observer. A value can be anything a number, a string, an object, etc.

The complete( ) handler

The complete() handler is fired when the Observable has no more items to send to its subscribed Observers.

The error( ) handler

The error() handler is called by the Observable if there is a problem when it is emitting data to the subscribed Observers.

These items that the Observables emit can be varied from a single click event, to a block of JSON data, to a series of messages from a backend push service. The Observable makes a non-blocking connection to its subscribed Observers, which allows items to be sent out over time to the Observer, each time calling the Observer’s next handler until there is either an error or all the items have been sent. It doesn’t matter what the items being sent are – the approach is the same. We create an Observable, register the Observers, and it’s not until the Observer’s Subscribe method is called that the items the Observable is loading will be called. Then, the Observable keeps calling the Observer’s next() handler until all the items have been pushed out by the Observable.

Example: Relationship between the Observable and the Observer

The following code should make the ...