work.suroh.tk/node_modules/rxjs/_esm2015/operators/concatMap.js

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2.9 KiB
JavaScript

import { mergeMap } from './mergeMap';
/* tslint:enable:max-line-length */
/**
* Projects each source value to an Observable which is merged in the output
* Observable, in a serialized fashion waiting for each one to complete before
* merging the next.
*
* <span class="informal">Maps each value to an Observable, then flattens all of
* these inner Observables using {@link concatAll}.</span>
*
* <img src="./img/concatMap.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 (so-called "inner") Observable. Each new inner Observable is
* concatenated with the previous inner Observable.
*
* __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: `concatMap` is equivalent to `mergeMap` with concurrency parameter set
* to `1`.
*
* @example <caption>For each click event, tick every second from 0 to 3, with no concurrency</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var result = clicks.concatMap(ev => Rx.Observable.interval(1000).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
*
* @see {@link concat}
* @see {@link concatAll}
* @see {@link concatMapTo}
* @see {@link exhaustMap}
* @see {@link mergeMap}
* @see {@link switchMap}
*
* @param {function(value: T, ?index: number): ObservableInput} project A function
* that, when applied to an item emitted by the source Observable, returns an
* Observable.
* @param {function(outerValue: T, innerValue: I, outerIndex: number, innerIndex: number): any} [resultSelector]
* A function to produce the value on the output Observable based on the values
* and the indices of the source (outer) emission and the inner Observable
* emission. The arguments passed to this function are:
* - `outerValue`: the value that came from the source
* - `innerValue`: the value that came from the projected Observable
* - `outerIndex`: the "index" of the value that came from the source
* - `innerIndex`: the "index" of the value from the projected Observable
* @return {Observable} An Observable that emits the result of applying the
* projection function (and the optional `resultSelector`) to each item emitted
* by the source Observable and taking values from each projected inner
* Observable sequentially.
* @method concatMap
* @owner Observable
*/
export function concatMap(project, resultSelector) {
return mergeMap(project, resultSelector, 1);
}
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