Returns the current value of the service
Attaches the given callback to the "change" event.
Function that will be called when the value of the service changes.
Detaches the given callback from the "change" event.
Function that was attached to the "change" event by the {@link aattach} method.
Deletes this subscription
Represents a subscription to a service. This interface allows getting the current value of the service and getting notifications on when the value is changed.