In the inheritance section we looked at one way to extend a class functionality, there is second way using delegation to extend functionality. With delegation, one object will contain a reference to a different object that it will hand off a request to perform the functionality.
The code below shows how to use delegation with the Bird class and Penguin class. The Penguin class has a reference to the Bird class and it delegates the call made to it's walk method over to Bird's walk method.
this.weight = weight;
this.height = height;
this.bird = bird;
const bird =newBird(...);
const penguin =newPenguin(bird);
A good discussion on 'behaviour delegation' can be found here.