@reactivex/rxjs/dist/cjs/src/observable/MulticastObservable.ts

Reactive Extensions for modern JavaScript

import {Observable} from '../Observable';
import {Subscriber} from '../Subscriber';
import {Subscription} from '../Subscription';
import {ConnectableObservable} from '../observable/ConnectableObservable';

export class MulticastObservable<T> extends Observable<T> {
  constructor(protected source: Observable<T>,
              private connectable: ConnectableObservable<T>,
              private selector: (source: Observable<T>) => Observable<T>) {
    super();
  }

  protected _subscribe(subscriber: Subscriber<T>): Subscription {
    const {selector, connectable} = this;

    const subscription = selector(connectable).subscribe(subscriber);
    subscription.add(connectable.connect());
    return subscription;
  }
}