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share.ts
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share.ts
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import { Subject } from '../Subject';
import { MonoTypeOperatorFunction, OperatorFunction, SubjectLike } from '../types';
import { SafeSubscriber } from '../Subscriber';
import { from } from '../observable/from';
import { operate } from '../util/lift';
export interface ShareConfig<T> {
/**
* The factory used to create the subject that will connect the source observable to
* multicast consumers.
*/
connector?: () => SubjectLike<T>;
/**
* If true, the resulting observable will reset internal state on error from source and return to a "cold" state. This
* allows the resulting observable to be "retried" in the event of an error.
* If false, when an error comes from the source it will push the error into the connecting subject, and the subject
* will remain the connecting subject, meaning the resulting observable will not go "cold" again, and subsequent retries
* or resubscriptions will resubscribe to that same subject. In all cases, RxJS subjects will emit the same error again, however
* {@link ReplaySubject} will also push its buffered values before pushing the error.
*/
resetOnError?: boolean;
/**
* If true, the resulting observable will reset internal state on completion from source and return to a "cold" state. This
* allows the resulting observable to be "repeated" after it is done.
* If false, when the source completes, it will push the completion through the connecting subject, and the subject
* will remain the connecting subject, meaning the resulting observable will not go "cold" again, and subsequent repeats
* or resubscriptions will resubscribe to that same subject.
*/
resetOnComplete?: boolean;
/**
* If true, when the number of subscribers to the resulting observable reaches zero due to those subscribers unsubscribing, the
* internal state will be reset and the resulting observable will return to a "cold" state. This means that the next
* time the resulting observable is subscribed to, a new subject will be created and the source will be subscribed to
* again.
* If false, when the number of subscribers to the resulting observable reaches zero due to unsubscription, the subject
* will remain connected to the source, and new subscriptions to the result will be connected through that same subject.
*/
resetOnRefCountZero?: boolean;
}
export function share<T>(): MonoTypeOperatorFunction<T>;
export function share<T>(options: ShareConfig<T>): MonoTypeOperatorFunction<T>;
/**
* Returns a new Observable that multicasts (shares) the original Observable. As long as there is at least one
* Subscriber this Observable will be subscribed and emitting data. When all subscribers have unsubscribed it will
* unsubscribe from the source Observable. Because the Observable is multicasting it makes the stream `hot`.
* This is an alias for `multicast(() => new Subject()), refCount()`.
*
* ![](share.png)
*
* ## Example
* Generate new multicast Observable from the source Observable value
* ```ts
* import { interval } from 'rxjs';
* import { share, map } from 'rxjs/operators';
*
* const source = interval(1000)
* .pipe(
* map((x: number) => {
* console.log('Processing: ', x);
* return x*x;
* }),
* share()
* );
*
* source.subscribe(x => console.log('subscription 1: ', x));
* source.subscribe(x => console.log('subscription 1: ', x));
*
* // Logs:
* // Processing: 0
* // subscription 1: 0
* // subscription 1: 0
* // Processing: 1
* // subscription 1: 1
* // subscription 1: 1
* // Processing: 2
* // subscription 1: 4
* // subscription 1: 4
* // Processing: 3
* // subscription 1: 9
* // subscription 1: 9
* // ... and so on
* ```
*
* @see {@link api/index/function/interval}
* @see {@link map}
*
* @return A function that returns an Observable that mirrors the source.
*/
export function share<T>(options?: ShareConfig<T>): OperatorFunction<T, T> {
options = options || {};
const { connector = () => new Subject<T>(), resetOnComplete = true, resetOnError = true, resetOnRefCountZero = true } = options;
let connection: SafeSubscriber<T> | null = null;
let subject: SubjectLike<T> | null = null;
let refCount = 0;
let hasCompleted = false;
let hasErrored = false;
// Used to reset the internal state to a "cold"
// state, as though it had never been subscribed to.
const reset = () => {
connection = subject = null;
hasCompleted = hasErrored = false;
};
return operate((source, subscriber) => {
refCount++;
// Create the subject if we don't have one yet.
subject = subject ?? connector();
// The following line adds the subscription to the subscriber passed.
// Basically, `subscriber === subject.subscribe(subscriber)` is `true`.
subject.subscribe(subscriber);
if (!connection) {
// We need to create a subscriber here - rather than pass an observer and
// assign the returned subscription to connection - because it's possible
// for reentrant subscriptions to the shared observable to occur and in
// those situations we want connection to be already-assigned so that we
// don't create another connection to the source.
connection = new SafeSubscriber({
next: (value: T) => subject!.next(value),
error: (err: any) => {
hasErrored = true;
// We need to capture the subject before
// we reset (if we need to reset).
const dest = subject!;
if (resetOnError) {
reset();
}
dest.error(err);
},
complete: () => {
hasCompleted = true;
const dest = subject!;
// We need to capture the subject before
// we reset (if we need to reset).
if (resetOnComplete) {
reset();
}
dest.complete();
},
});
from(source).subscribe(connection);
}
// This is also added to `subscriber`, technically.
return () => {
refCount--;
// If we're resetting on refCount === 0, and it's 0, we only want to do
// that on "unsubscribe", really. Resetting on error or completion is a different
// configuration.
if (resetOnRefCountZero && !refCount && !hasErrored && !hasCompleted) {
// We need to capture the connection before
// we reset (if we need to reset).
const conn = connection;
reset();
conn?.unsubscribe();
}
};
});
}