work.suroh.tk/node_modules/rxjs/_esm5/operator/expand.js

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2019-12-02 12:22:45 +00:00
/** PURE_IMPORTS_START .._operators_expand PURE_IMPORTS_END */
import { expand as higherOrder } from '../operators/expand';
/* 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>
*
* <img src="./img/expand.png" width="100%">
*
* 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 <caption>Start emitting the powers of two on every click, at most 10 of them</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var powersOfTwo = clicks
* .mapTo(1)
* .expand(x => Rx.Observable.of(2 * x).delay(1000))
* .take(10);
* powersOfTwo.subscribe(x => console.log(x));
*
* @see {@link mergeMap}
* @see {@link mergeScan}
*
* @param {function(value: T, index: number) => Observable} project A function
* that, when applied to an item emitted by the source or the output Observable,
* returns an Observable.
* @param {number} [concurrent=Number.POSITIVE_INFINITY] Maximum number of input
* Observables being subscribed to concurrently.
* @param {Scheduler} [scheduler=null] The IScheduler to use for subscribing to
* each projected inner Observable.
* @return {Observable} An Observable that emits the source values and also
* result of applying the projection function to each value emitted on the
* output Observable and and merging the results of the Observables obtained
* from this transformation.
* @method expand
* @owner Observable
*/
export function expand(project, concurrent, scheduler) {
if (concurrent === void 0) {
concurrent = Number.POSITIVE_INFINITY;
}
if (scheduler === void 0) {
scheduler = undefined;
}
concurrent = (concurrent || 0) < 1 ? Number.POSITIVE_INFINITY : concurrent;
return higherOrder(project, concurrent, scheduler)(this);
}
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