The YUI Global Object: Compose Classes of Objects with augment
In this example, a class has been created then augmented with
EventTarget to provide custom event functionality.
Click the Send button to send the instance of the new class a request.
Using augment
Instantiate YUI
The example: Any class can be an EventTarget
This example creates a custom class, then augments it with
EventTarget (functionality included in the YUI Event Utility). Using the
packaged functionality of EventTarget, the code for
Foo is able to focus on the functionality unique to its
purpose.
Composition, not inheritance
If Foo were a part of a class hierarchy, it would be improper
to include EventTarget in the inheritance chain, because its custom event
functionality is not an intrinsic characteristic but rather an ancillary, generic
capability that many classes share.
Unlike extended classes, the relationship between a class and
the classes augmenting it is not an indication of type hierarchy. The intent
of augment is to aid in extracting nonessential behaviors or
behaviors shared by many classes, allowing for a composition-style class
architecture.
This may appear similar to multiple inheritance, but it's not.
augment simply adds the public methods and members from one class
prototype to another class prototype. Instances of the augmented class will
not pass instanceof tests for the class(es) which augmented
it.