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>
Parameters
| project |
A function
that, when applied to an item emitted by the source Observable, returns an
Observable.
|
| resultSelector |
Optional. Default is undefined.
Type: (outerValue: T, innerValue: ObservedValueOf, outerIndex: number, innerIndex: number) => R.
|
Returns
OperatorFunction<T, ObservedValueOf<O> | R>: 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.
Description
Maps each value to an Observable, then flattens all of
these inner Observables.
Returns an Observable that emits items based on applying a function that you
supply to each item emitted by the source Observable, where that function
returns an (so-called "inner") Observable. Each time it observes one of these
inner Observables, the output Observable begins emitting the items emitted by
that inner Observable. When a new inner Observable is emitted, switchMap
stops emitting items from the earlier-emitted inner Observable and begins
emitting items from the new one. It continues to behave like this for
subsequent inner Observables.
Example
Rerun an interval Observable on every click event
import { fromEvent, interval } from 'rxjs';
import { switchMap } from 'rxjs/operators';
const clicks = fromEvent(document, 'click');
const result = clicks.pipe(switchMap((ev) => interval(1000)));
result.subscribe(x => console.log(x));
Overloads
switchMap(project: (value: T, index: number) => O): OperatorFunction<T, ObservedValueOf<O>>
Parameters
| project |
Type: (value: T, index: number) => O.
|
Returns
OperatorFunction<T, ObservedValueOf<O>>
|
switchMap(project: (value: T, index: number) => O, resultSelector: undefined): OperatorFunction<T, ObservedValueOf<O>>
Parameters
| project |
Type: (value: T, index: number) => O.
|
| resultSelector |
Type: undefined.
|
Returns
OperatorFunction<T, ObservedValueOf<O>>
|
switchMap(project: (value: T, index: number) => O, resultSelector: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R): OperatorFunction<T, R>
Parameters
| project |
Type: (value: T, index: number) => O.
|
| resultSelector |
Type: (outerValue: T, innerValue: ObservedValueOf, outerIndex: number, innerIndex: number) => R.
|
Returns
OperatorFunction<T, R>
|