Projects each source value to the same Observable which is merged multiple
times in a serialized fashion on the output Observable.
concatMapTo<T, R, O extends ObservableInput<any>>(innerObservable: O, resultSelector?: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R): OperatorFunction<T, ObservedValueOf<O> | R>
Parameters
| innerObservable |
An Observable to replace each value from
the source Observable.
|
| resultSelector |
Optional. Default is undefined.
Type: (outerValue: T, innerValue: ObservedValueOf, outerIndex: number, innerIndex: number) => R.
|
Returns
OperatorFunction<T, ObservedValueOf<O> | R>: An observable of values merged together by joining the
passed observable with itself, one after the other, for each value emitted
from the source.
Description
It's like concatMap, but maps each value
always to the same inner Observable.
Maps each source value to the given Observable innerObservable regardless
of the source value, and then flattens those resulting Observables into one
single Observable, which is the output Observable. Each new innerObservable
instance emitted on the output Observable is concatenated with the previous
innerObservable instance.
Warning: if source values arrive endlessly and faster than their
corresponding inner Observables can complete, it will result in memory issues
as inner Observables amass in an unbounded buffer waiting for their turn to
be subscribed to.
Note: concatMapTo is equivalent to mergeMapTo with concurrency parameter
set to 1.
Example
For each click event, tick every second from 0 to 3, with no concurrency
import { fromEvent, interval } from 'rxjs';
import { concatMapTo, take } from 'rxjs/operators';
const clicks = fromEvent(document, 'click');
const result = clicks.pipe(
concatMapTo(interval(1000).pipe(take(4))),
);
result.subscribe(x => console.log(x));
// Results in the following:
// (results are not concurrent)
// For every click on the "document" it will emit values 0 to 3 spaced
// on a 1000ms interval
// one click = 1000ms-> 0 -1000ms-> 1 -1000ms-> 2 -1000ms-> 3
Overloads
concatMapTo(observable: O): OperatorFunction<T, ObservedValueOf<O>>
Parameters
Returns
OperatorFunction<T, ObservedValueOf<O>>
|
concatMapTo(observable: O, resultSelector: undefined): OperatorFunction<T, ObservedValueOf<O>>
Parameters
| observable |
Type: O.
|
| resultSelector |
Type: undefined.
|
Returns
OperatorFunction<T, ObservedValueOf<O>>
|
concatMapTo(observable: O, resultSelector: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R): OperatorFunction<T, R>
Parameters
| observable |
Type: O.
|
| resultSelector |
Type: (outerValue: T, innerValue: ObservedValueOf, outerIndex: number, innerIndex: number) => R.
|
Returns
OperatorFunction<T, R>
|