Returns an Observable that mirrors the source Observable as long as there is at least one subscriber subscribed to the
given topic. When the subscription count on the given topic drops to zero, the returned Observable completes. If there
is no topic subscription present at the time when subscribing to the Observable, then it completes immediately.
This operator is similar to the RxJS takeUntil operator, but accepts a topic instead of a notifier Observable.
Returns an Observable that mirrors the source Observable as long as there is at least one subscriber subscribed to the given topic. When the subscription count on the given topic drops to zero, the returned Observable completes. If there is no topic subscription present at the time when subscribing to the Observable, then it completes immediately.
This operator is similar to the RxJS takeUntil operator, but accepts a topic instead of a notifier Observable.