how to use the flatmap function from the rxjs library in javascript

The flatMap function in rxjs is used to flatten and merge a higher-order observable. It can be used to transform the values emitted by an observable, and then merge the resulting observables.

Here's an example usage of flatMap:

index.tsx
import { of } from 'rxjs';
import { flatMap } from 'rxjs/operators';

const letters$ = of('a', 'b', 'c');

letters$
  .pipe(
    flatMap((letter) => of(`${letter.toUpperCase()}1`, `${letter.toUpperCase()}2`))
  )
  .subscribe((value) => console.log(value));

// Output:
// A1
// A2
// B1
// B2
// C1
// C2
306 chars
19 lines

In this code snippet, we start by creating an observable letters$ that emits a, b, and c. We then use the flatMap operator to transform each of those letters into an observable that emits two values: the uppercase letter followed by either 1 or 2.

Finally, we use the subscribe method to log each of the emitted values.