What is an Observer ?

An Observer in the context of Angular and RxJS is an interface that represents a consumer of push-based notifications delivered by an Observable. It is essentially a set of callback methods that define how to handle the data or events received from an Observable. These callback methods include:

• next: This method is called to deliver the next value from the Observable. It is invoked whenever the Observable emits a new piece of data.
• error: This method is called when the Observable encounters an error condition. It handles any errors that occur during the Observable execution.
• complete: This method is called when the Observable successfully completes its sequence of data emissions.

Here is a basic structure of an Observer:

interface Observer<T> {
  next: (value: T) => void;
  error: (err: any) => void;
  complete: () => void;
}

When subscribing to an Observable, you can pass an Observer to handle the data, errors, and completion notifications. For example:

const myObservable = new Observable(subscriber => {
  subsc...