Deep Dive Into The RxJs mergeMap Operator: How Does it Work?

The mergeMap operator in RxJS is a powerful and commonly used operator for transforming the items emitted by an observable into other observables, and then flattening those observables into a single observable sequence. It's often referred to as a "flatMap" operator as well.

Here’s a deep dive into how mergeMap works:

Basic Syntax:

import { of } from 'rxjs';
import { mergeMap } from 'rxjs/operators';

const source = of('a', 'b', 'c');

source.pipe(
  mergeMap(value => /* Observable or Promise */)
).subscribe(result => console.log(result));

How it Works:

Mapping Function:

• For each item emitted by the source observable (source in the example), the mergeMap operator applies a mapping function.
• The mapping function takes the current value emitted by the source observable and returns a new observable or a promise.

Flattening:

• mergeMap then subscribes to the observable or waits for the promise to resolve.
• If the mapping function returns an observable, mergeMap flattens it by merging its emissions into the output observable.
• If the mapping function returns a…