Applies an accumulator function over the source Observable where the
accumulator function itself returns an Observable, then each intermediate
Observable returned is merged into the output Observable.
mergeScan<T, R>(accumulator: (acc: R, value: T, index: number) => ObservableInput<R>, seed: R, concurrent: number = Number.POSITIVE_INFINITY): OperatorFunction<T, R>
Parameters
| accumulator |
The accumulator function called on each source value.
|
| seed |
The initial accumulation value.
|
| concurrent |
Optional. Default is Number.POSITIVE_INFINITY.
Maximum number of
input Observables being subscribed to concurrently.
|
Returns
OperatorFunction<T, R>: An observable of the accumulated values.
Description
It's like scan, but the Observables returned
by the accumulator are merged into the outer Observable.
Example
Count the number of click events
import { fromEvent, of } from 'rxjs';
import { mapTo } from 'rxjs/operators';
const click$ = fromEvent(document, 'click');
const one$ = click$.pipe(mapTo(1));
const seed = 0;
const count$ = one$.pipe(
mergeScan((acc, one) => of(acc + one), seed),
);
count$.subscribe(x => console.log(x));
// Results:
1
2
3
4
// ...and so on for each click