The Basic of Observable

Observables provides support for passing messages between publishers and subscribers. So in Angular the observables can used in th eplaces such as event handling, asynchronous programming and handling multiple values

The observer functions are executed only when a consumer subscribes to it. The subscribed consumer then receives notifications until the function completes or until they unsubscribe.

Basic Usage

As a publisher, you create an Observable instance that defines a subscriber function. This is the function that is executed when a consumer calls the subscribe() method. The subscriber function defines how to obtain or generate values or messages to be published.

To execute the observable you have created and begin receiving notifications, you call its subscribe() method, passing an observer. This is a JavaScript object that defines the handlers for the notifications you receive. The subscribe() call returns a Subscription object that has an unsubscribe() method, which you call to stop receiving notifications.

A handler for receiving observable notifications implements the Observer interface. It is an object that defines callback methods to handle the three types of notifications that an observable can send:

Lets create a basic observable using RxJs

Here we created an Observable named 'observable' and calling its subscribe method by passing the observer object. Once it calls the subscrible method the observer will become executed and here it is executed only the first two next functions, In shot we can say its only executed the function before the complete() method. the remaining functions wont executed. Similarly if an error executes then the remaining next functions wont executed.

Here follows the output of above program