InternalReadonlyidInit input
ReadonlyloadReadonly InternalsourceUsed to store the current source id and make sure removeSource is only called once.
A callback method that performs custom clean-up, invoked immediately before a directive, pipe, or service instance is destroyed.
A callback method that is invoked immediately after the default change detector has checked the directive's data-bound properties for the first time, and before any of the view or content children have been checked. It is invoked only once when the directive is instantiated.
A composition object for the source components