switchMapTo

signature: switchMapTo(innerObservable: Observable, resultSelector: function(outerValue, innerValue, outerIndex, innerIndex): any): Observable

Map to same inner observable, complete previous inner observable.

💡 If you need to consider the emitted value from the source, try switchMap!

Ultimate RxJS

Examples

Example 1: Restart countdown on click, until countdown completes one time

( StackBlitz )

// RxJS v6+
import { interval, fromEvent } from 'rxjs';
import {
switchMapTo,
scan,
startWith,
takeWhile,
finalize
} from 'rxjs/operators';
const COUNTDOWN_TIME = 10;
// reference
const countdownElem = document.getElementById('countdown');
// streams
const click$ = fromEvent(document, 'click');
const countdown$ = interval(1000).pipe(
scan((acc, _) => --acc, COUNTDOWN_TIME),
startWith(COUNTDOWN_TIME)
);
click$
.pipe(
switchMapTo(countdown$),
takeWhile(val => val >= 0),
finalize(() => (countdownElem.innerHTML = "We're done here!"))
)
.subscribe((val: any) => (countdownElem.innerHTML = val));

Additional Resources

📁 Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/switchMapTo.ts