Optionaltarget: {}Remove a single observer.
the observable to observe
the observer function
Optionaltarget: {}if the observer was bound in on this must match the bound target
Add an observer.
the observable to observe
the observer function
Optionaltarget: {}optional "this" to bind the observer
A collection of observers managed as a unit. This makes it convenient to deregister multiple observers when an object closes.