rxjs/src/internal/operators/share.ts

Reactive Extensions for modern JavaScript

import { Observable } from '../Observable';
import { multicast } from './multicast';
import { refCount } from './refCount';
import { Subject } from '../Subject';

import { MonoTypeOperatorFunction } from '../types';

function shareSubjectFactory() {
  return new Subject<any>();
}

/**
 * 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
 * ```typescript
 * 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 {Observable<T>} An Observable that upon connection causes the source Observable to emit items to its Observers.
 */
export function share<T>(): MonoTypeOperatorFunction<T> {
  return (source: Observable<T>) => refCount()(multicast(shareSubjectFactory)(source)) as Observable<T>;
}