es6/observable/ForkJoinObservable.js
import { Observable } from '../Observable';
import { EmptyObservable } from './EmptyObservable';
import { isArray } from '../util/isArray';
import { subscribeToResult } from '../util/subscribeToResult';
import { OuterSubscriber } from '../OuterSubscriber';
/**
* We need this JSDoc comment for affecting ESDoc.
* @extends {Ignored}
* @hide true
*/
export class ForkJoinObservable extends Observable {
constructor(sources, resultSelector) {
super();
this.sources = sources;
this.resultSelector = resultSelector;
}
/* tslint:enable:max-line-length */
/**
* Joins last values emitted by passed Observables.
*
* <span class="informal">Wait for Observables to complete and then combine last values they emitted.</span>
*
* <img src="./img/forkJoin.png" width="100%">
*
* `forkJoin` is an operator that takes any number of Observables which can be passed either as an array
* or directly as arguments. If no input Observables are provided, resulting stream will complete
* immediately.
*
* `forkJoin` will wait for all passed Observables to complete and then it will emit an array with last
* values from corresponding Observables. So if you pass `n` Observables to the operator, resulting
* array will have `n` values, where first value is the last thing emitted by the first Observable,
* second value is the last thing emitted by the second Observable and so on. 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 lifecycle of passed Observables, but also throughout it, try out {@link combineLatest}
* or {@link zip} instead.
*
* In order for resulting array to have the same length as the number of input Observables, whenever any of
* that 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 as well,
* unless at any point some other Observable completes without emitting value, which brings us back to
* the previous case. Overall, in order for `forkJoin` to emit a value, all Observables passed as arguments
* have to emit something at least once and complete.
*
* If any input Observable errors at some point, `forkJoin` will error as well and all other Observables
* will be immediately unsubscribed.
*
* Optionally `forkJoin` accepts project function, that will be called with values which normally
* would land in emitted array. Whatever is returned by project function, will appear in output
* Observable instead. This means that default project can be thought of as a function that takes
* all its arguments and puts them into an array. Note that project function will be called only
* when output Observable is supposed to emit a result.
*
* @example <caption>Use forkJoin with operator emitting immediately</caption>
* const observable = Rx.Observable.forkJoin(
* Rx.Observable.of(1, 2, 3, 4),
* Rx.Observable.of(5, 6, 7, 8)
* );
* observable.subscribe(
* value => console.log(value),
* err => {},
* () => console.log('This is how it ends!')
* );
*
* // Logs:
* // [4, 8]
* // "This is how it ends!"
*
*
* @example <caption>Use forkJoin with operator emitting after some time</caption>
* const observable = Rx.Observable.forkJoin(
* Rx.Observable.interval(1000).take(3), // emit 0, 1, 2 every second and complete
* Rx.Observable.interval(500).take(4) // emit 0, 1, 2, 3 every half a second and complete
* );
* observable.subscribe(
* value => console.log(value),
* err => {},
* () => console.log('This is how it ends!')
* );
*
* // Logs:
* // [2, 3] after 3 seconds
* // "This is how it ends!" immediately after
*
*
* @example <caption>Use forkJoin with project function</caption>
* const observable = Rx.Observable.forkJoin(
* Rx.Observable.interval(1000).take(3), // emit 0, 1, 2 every second and complete
* Rx.Observable.interval(500).take(4), // emit 0, 1, 2, 3 every half a second and complete
* (n, m) => n + m
* );
* observable.subscribe(
* value => console.log(value),
* err => {},
* () => console.log('This is how it ends!')
* );
*
* // Logs:
* // 5 after 3 seconds
* // "This is how it ends!" immediately after
*
* @see {@link combineLatest}
* @see {@link zip}
*
* @param {...SubscribableOrPromise} sources 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.
* @static true
* @name forkJoin
* @owner Observable
*/
static create(...sources) {
if (sources === null || arguments.length === 0) {
return new EmptyObservable();
}
let resultSelector = null;
if (typeof sources[sources.length - 1] === 'function') {
resultSelector = sources.pop();
}
// if the first and only other argument besides the resultSelector is an array
// assume it's been called with `forkJoin([obs1, obs2, obs3], resultSelector)`
if (sources.length === 1 && isArray(sources[0])) {
sources = sources[0];
}
if (sources.length === 0) {
return new EmptyObservable();
}
return new ForkJoinObservable(sources, resultSelector);
}
_subscribe(subscriber) {
return new ForkJoinSubscriber(subscriber, this.sources, this.resultSelector);
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class ForkJoinSubscriber extends OuterSubscriber {
constructor(destination, sources, resultSelector) {
super(destination);
this.sources = sources;
this.resultSelector = resultSelector;
this.completed = 0;
this.haveValues = 0;
const len = sources.length;
this.total = len;
this.values = new Array(len);
for (let i = 0; i < len; i++) {
const source = sources[i];
const innerSubscription = subscribeToResult(this, source, null, i);
if (innerSubscription) {
innerSubscription.outerIndex = i;
this.add(innerSubscription);
}
}
}
notifyNext(outerValue, innerValue, outerIndex, innerIndex, innerSub) {
this.values[outerIndex] = innerValue;
if (!innerSub._hasValue) {
innerSub._hasValue = true;
this.haveValues++;
}
}
notifyComplete(innerSub) {
const destination = this.destination;
const { haveValues, resultSelector, values } = this;
const len = values.length;
if (!innerSub._hasValue) {
destination.complete();
return;
}
this.completed++;
if (this.completed !== len) {
return;
}
if (haveValues === len) {
const value = resultSelector ? resultSelector.apply(this, values) : values;
destination.next(value);
}
destination.complete();
}
}
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