# 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`](/learn-rxjs/operators/transformation/switchmap.md)!

***

### Examples

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

( [StackBlitz](https://stackblitz.com/edit/typescript-r97ngc?file=index.ts) )

```js
// 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

* [switchMapTo](https://rxjs.dev/api/operators/switchMapTo) 📰 - Official docs

***

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


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