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- import { OperatorFunction, ObservableInput, ObservedValueOf, SchedulerLike } from '../types';
- import { operate } from '../util/lift';
- import { mergeInternals } from './mergeInternals';
- /* tslint:disable:max-line-length */
- export function expand<T, O extends ObservableInput<unknown>>(
- project: (value: T, index: number) => O,
- concurrent?: number,
- scheduler?: SchedulerLike
- ): OperatorFunction<T, ObservedValueOf<O>>;
- /**
- * @deprecated The `scheduler` parameter will be removed in v8. If you need to schedule the inner subscription,
- * use `subscribeOn` within the projection function: `expand((value) => fn(value).pipe(subscribeOn(scheduler)))`.
- * Details: Details: https://rxjs.dev/deprecations/scheduler-argument
- */
- export function expand<T, O extends ObservableInput<unknown>>(
- project: (value: T, index: number) => O,
- concurrent: number | undefined,
- scheduler: SchedulerLike
- ): OperatorFunction<T, ObservedValueOf<O>>;
- /* tslint:enable:max-line-length */
- /**
- * Recursively projects each source value to an Observable which is merged in
- * the output Observable.
- *
- * <span class="informal">It's similar to {@link mergeMap}, but applies the
- * projection function to every source value as well as every output value.
- * It's recursive.</span>
- *
- * 
- *
- * 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 Observable, and then merging those resulting Observables and
- * emitting the results of this merger. *Expand* will re-emit on the output
- * Observable every source value. Then, each output value is given to the
- * `project` function which returns an inner Observable to be merged on the
- * output Observable. Those output values resulting from the projection are also
- * given to the `project` function to produce new output values. This is how
- * *expand* behaves recursively.
- *
- * ## Example
- *
- * Start emitting the powers of two on every click, at most 10 of them
- *
- * ```ts
- * import { fromEvent, map, expand, of, delay, take } from 'rxjs';
- *
- * const clicks = fromEvent(document, 'click');
- * const powersOfTwo = clicks.pipe(
- * map(() => 1),
- * expand(x => of(2 * x).pipe(delay(1000))),
- * take(10)
- * );
- * powersOfTwo.subscribe(x => console.log(x));
- * ```
- *
- * @see {@link mergeMap}
- * @see {@link mergeScan}
- *
- * @param project A function that, when applied to an item emitted by the source
- * or the output Observable, returns an Observable.
- * @param concurrent Maximum number of input Observables being subscribed to
- * concurrently.
- * @param scheduler The {@link SchedulerLike} to use for subscribing to
- * each projected inner Observable.
- * @return A function that returns an Observable that emits the source values
- * and also result of applying the projection function to each value emitted on
- * the output Observable and merging the results of the Observables obtained
- * from this transformation.
- */
- export function expand<T, O extends ObservableInput<unknown>>(
- project: (value: T, index: number) => O,
- concurrent = Infinity,
- scheduler?: SchedulerLike
- ): OperatorFunction<T, ObservedValueOf<O>> {
- concurrent = (concurrent || 0) < 1 ? Infinity : concurrent;
- return operate((source, subscriber) =>
- mergeInternals(
- // General merge params
- source,
- subscriber,
- project,
- concurrent,
- // onBeforeNext
- undefined,
- // Expand-specific
- true, // Use expand path
- scheduler // Inner subscription scheduler
- )
- );
- }
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