What is an Observable ?

An Observable in Angular and RxJS is a foundational concept used extensively in reactive programming to handle asynchronous operations and data streams. It is a core primitive representing a lazy, push-based collection that can emit multiple values over time, allowing developers to handle asynchronous operations more effectively[1].

Characteristics of Observables

• Lazy Execution: Observables are lazy by nature, meaning they do not start emitting values until a subscriber actively subscribes to them[1].
• Push-based: Observables push values to the subscribers as they become available, which is different from pull-based systems where the consumer requests data[1].
• Multiple Values: Unlike Promises, which resolve a single value, Observables can emit multiple values over time, making them suitable for handling streams of data such as user input, HTTP requests, and other continuous data sources[1][4].

Usage in Angular

In Angular, Observables are used to manage asynchronous tasks such as handling user interactions, HTTP requests, and real-time updates. Angular's HTTP module, for example, returns Observables from HTTP method calls, allowing developers to subscribe to these Observables to handle asynchronous HTTP responses[1][19].

Subscription and Unsubscription

To receive values from an Observable, a subscriber must subscribe to it. The subscription remains active until the subscriber decides to unsubscribe, which is crucial for preventing memory leaks, especially in long-lived subscriptions[1].

Example

Here’s a basic example of creating and subscribing to an Observable in Angular using RxJS:

import { Observable } from 'rxjs';

const myObservable = new Observable(observer => {
  observer.next('First value');
  observer.next('Second value');
  setTimeout(() => {
    observer.next('Value after delay');
    observer.complete();
  }, 2000);
});

myObservable.subscribe({
  next: data => console.log('Data:', data),
  error: err => console.log('Error:', err),
  complete: () => cons...