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forkJoin.ts
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forkJoin.ts
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import { Observable } from '../Observable';
import { ObservedValueOf, ObservableInputTuple, ObservableInput } from '../types';
import { argsArgArrayOrObject } from '../util/argsArgArrayOrObject';
import { innerFrom } from './from';
import { popResultSelector } from '../util/args';
import { OperatorSubscriber } from '../operators/OperatorSubscriber';
import { mapOneOrManyArgs } from '../util/mapOneOrManyArgs';
import { createObject } from '../util/createObject';
export function forkJoin(scheduler: null | undefined): Observable<never>;
// forkJoin([a, b, c])
export function forkJoin(sources: readonly []): Observable<never>;
export function forkJoin<A extends readonly unknown[]>(sources: readonly [...ObservableInputTuple<A>]): Observable<A>;
/** @deprecated resultSelector is deprecated, pipe to map instead */
export function forkJoin<A extends readonly unknown[], R>(
sources: readonly [...ObservableInputTuple<A>],
resultSelector: (...values: A) => R
): Observable<R>;
// forkJoin(a, b, c)
/** @deprecated Use the version that takes an array of Observables instead, Details https://rxjs.dev/deprecations/array-argument */
export function forkJoin<A extends readonly unknown[]>(...sources: [...ObservableInputTuple<A>]): Observable<A>;
/** @deprecated resultSelector is deprecated, pipe to map instead */
export function forkJoin<A extends readonly unknown[], R>(
...sourcesAndResultSelector: [...ObservableInputTuple<A>, (...values: A) => R]
): Observable<R>;
// forkJoin({a, b, c})
export function forkJoin(sourcesObject: { [K in any]: never }): Observable<never>;
export function forkJoin<T extends Record<string, ObservableInput<any>>>(
sourcesObject: T
): Observable<{ [K in keyof T]: ObservedValueOf<T[K]> }>;
/**
* Accepts an `Array` of {@link ObservableInput} or a dictionary `Object` of {@link ObservableInput} and returns
* an {@link Observable} that emits either an array of values in the exact same order as the passed array,
* or a dictionary of values in the same shape as the passed dictionary.
*
* <span class="informal">Wait for Observables to complete and then combine last values they emitted;
* complete immediately if an empty array is passed.</span>
*
* ![](forkJoin.png)
*
* `forkJoin` is an operator that takes any number of input observables which can be passed either as an array
* or a dictionary of input observables. If no input observables are provided (e.g. an empty array is passed),
* then the resulting stream will complete immediately.
*
* `forkJoin` will wait for all passed observables to emit and complete and then it will emit an array or an object with last
* values from corresponding observables.
*
* If you pass an array of `n` observables to the operator, then the resulting
* array will have `n` values, where the first value is the last one emitted by the first observable,
* second value is the last one emitted by the second observable and so on.
*
* If you pass a dictionary of observables to the operator, then the resulting
* objects will have the same keys as the dictionary passed, with their last values they have emitted
* located at the corresponding key.
*
* That means `forkJoin` will not emit more than once and it will complete after that. If you need to emit combined
* values not only at the end of the lifecycle of passed observables, but also throughout it, try out {@link combineLatest}
* or {@link zip} instead.
*
* In order for the resulting array to have the same length as the number of input observables, whenever any of
* the given observables completes without emitting any value, `forkJoin` will complete at that moment as well
* and it will not emit anything either, even if it already has some last values from other observables.
* Conversely, if there is an observable that never completes, `forkJoin` will never complete either,
* unless at any point some other observable completes without emitting a value, which brings us back to
* the previous case. Overall, in order for `forkJoin` to emit a value, all given observables
* have to emit something at least once and complete.
*
* If any given observable errors at some point, `forkJoin` will error as well and immediately unsubscribe
* from the other observables.
*
* Optionally `forkJoin` accepts a `resultSelector` function, that will be called with values which normally
* would land in the emitted array. Whatever is returned by the `resultSelector`, will appear in the output
* observable instead. This means that the default `resultSelector` can be thought of as a function that takes
* all its arguments and puts them into an array. Note that the `resultSelector` will be called only
* when `forkJoin` is supposed to emit a result.
*
* ## Examples
*
* ### Use forkJoin with a dictionary of observable inputs
* ```ts
* import { forkJoin, of, timer } from 'rxjs';
*
* const observable = forkJoin({
* foo: of(1, 2, 3, 4),
* bar: Promise.resolve(8),
* baz: timer(4000),
* });
* observable.subscribe({
* next: value => console.log(value),
* complete: () => console.log('This is how it ends!'),
* });
*
* // Logs:
* // { foo: 4, bar: 8, baz: 0 } after 4 seconds
* // "This is how it ends!" immediately after
* ```
*
* ### Use forkJoin with an array of observable inputs
* ```ts
* import { forkJoin, of, timer } from 'rxjs';
*
* const observable = forkJoin([
* of(1, 2, 3, 4),
* Promise.resolve(8),
* timer(4000),
* ]);
* observable.subscribe({
* next: value => console.log(value),
* complete: () => console.log('This is how it ends!'),
* });
*
* // Logs:
* // [4, 8, 0] after 4 seconds
* // "This is how it ends!" immediately after
* ```
*
* @see {@link combineLatest}
* @see {@link zip}
*
* @param {...ObservableInput} args Any number of Observables provided either as an array or as an arguments
* passed directly to the operator.
* @param {function} [project] Function that takes values emitted by input Observables and returns value
* that will appear in resulting Observable instead of default array.
* @return {Observable} Observable emitting either an array of last values emitted by passed Observables
* or value from project function.
*/
export function forkJoin(...args: any[]): Observable<any> {
const resultSelector = popResultSelector(args);
const { args: sources, keys } = argsArgArrayOrObject(args);
const result = new Observable((subscriber) => {
const { length } = sources;
if (!length) {
subscriber.complete();
return;
}
const values = new Array(length);
let remainingCompletions = length;
let remainingEmissions = length;
for (let sourceIndex = 0; sourceIndex < length; sourceIndex++) {
let hasValue = false;
innerFrom(sources[sourceIndex]).subscribe(
new OperatorSubscriber(
subscriber,
(value) => {
if (!hasValue) {
hasValue = true;
remainingEmissions--;
}
values[sourceIndex] = value;
},
() => {
if (!--remainingCompletions || !hasValue) {
if (!remainingEmissions) {
subscriber.next(keys ? createObject(keys, values) : values);
}
subscriber.complete();
}
}
)
);
}
});
return resultSelector ? result.pipe(mapOneOrManyArgs(resultSelector)) : result;
}