SwitchMap

Projects each source value to an Observable which is merged in the output Observable, emitting values only from the most recently projected Observable.

switchMap<T, R, O extends ObservableInput<any>>(project: (value: T, index: number) => O, resultSelector?: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R): OperatorFunction<T, ObservedValueOf<O> | R>

OperatorFunction<T, ObservedValueOf | R>: A function that returns an Observable that emits the result of applying the projection function (and the optional deprecated resultSelector) to each item emitted by the source Observable and taking only the values from the most recently projected inner Observable.

Generate new Observable according to source Observable values

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

const switched = of(1, 2, 3).pipe(switchMap((x: number) => of(x, x ** 2, x ** 3)));
switched.subscribe(x => console.log(x));
// outputs
// 1
// 1
// 1
// 2
// 4
// 8
// ... and so on