This flag indicates whether the observable is asynchronous. Any observable that accepts promise returns may be asynchronous but this information is not available at runtime unless you specify here, typically via AsyncObservable.
True if there is at least one observer registered.
Notify observers.
Rest
...args: TDetermine whether an observer is registered.
Remove an observer.
Add an observer.
Add an observer that emits once then is unregistered.
An Observable that explicitly supports asynchronous observers.