52 lines
2.4 KiB
JavaScript
52 lines
2.4 KiB
JavaScript
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import { expand as higherOrder } from '../operators/expand';
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/* tslint:enable:max-line-length */
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/**
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* Recursively projects each source value to an Observable which is merged in
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* the output Observable.
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*
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* <span class="informal">It's similar to {@link mergeMap}, but applies the
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* projection function to every source value as well as every output value.
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* It's recursive.</span>
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*
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* <img src="./img/expand.png" width="100%">
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*
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* Returns an Observable that emits items based on applying a function that you
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* supply to each item emitted by the source Observable, where that function
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* returns an Observable, and then merging those resulting Observables and
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* emitting the results of this merger. *Expand* will re-emit on the output
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* Observable every source value. Then, each output value is given to the
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* `project` function which returns an inner Observable to be merged on the
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* output Observable. Those output values resulting from the projection are also
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* given to the `project` function to produce new output values. This is how
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* *expand* behaves recursively.
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*
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* @example <caption>Start emitting the powers of two on every click, at most 10 of them</caption>
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* var clicks = Rx.Observable.fromEvent(document, 'click');
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* var powersOfTwo = clicks
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* .mapTo(1)
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* .expand(x => Rx.Observable.of(2 * x).delay(1000))
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* .take(10);
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* powersOfTwo.subscribe(x => console.log(x));
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*
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* @see {@link mergeMap}
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* @see {@link mergeScan}
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*
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* @param {function(value: T, index: number) => Observable} project A function
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* that, when applied to an item emitted by the source or the output Observable,
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* returns an Observable.
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* @param {number} [concurrent=Number.POSITIVE_INFINITY] Maximum number of input
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* Observables being subscribed to concurrently.
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* @param {Scheduler} [scheduler=null] The IScheduler to use for subscribing to
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* each projected inner Observable.
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* @return {Observable} An Observable that emits the source values and also
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* result of applying the projection function to each value emitted on the
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* output Observable and and merging the results of the Observables obtained
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* from this transformation.
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* @method expand
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* @owner Observable
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*/
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export function expand(project, concurrent = Number.POSITIVE_INFINITY, scheduler = undefined) {
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concurrent = (concurrent || 0) < 1 ? Number.POSITIVE_INFINITY : concurrent;
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return higherOrder(project, concurrent, scheduler)(this);
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}
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//# sourceMappingURL=expand.js.map
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