Multiply Defense - HTML5 Game Development - page 126

The code creates a new object with the given parameter as the prototype. We defined the
RectShape funcion as a constructor. That makes the RectShape prototype a new object
along with the Container prototype. The following igure shows the prototype relaionship
when we create a new RectShape instance:
The following Mozilla Developer Network aricle shows an example of class inheritance using
Object.create :
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/
Global_Objects/Object/create
There is one more step to make the inheritance work. The Container object has its
own constructor to iniialize its logic. We need to call the parent deiniion funcion or
"constructor" in an object-oriented programming term inside our custom RectShape
class as follows:
createjs.Container.call(this);
We haven't changed the namespace, so we need the createjs namespace whenever we
refer to the Container class. In JavaScript, class is a concept. In reality, Container is a
funcion object. So we can invoke the Container funcion to iniialize it. This has the same
effect of calling super() in other class-based, object-oriented programming languages.
The following essay provides an introducion to applying the object-oriented programming
technique in JavaScript:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Introduction_
to_Object-Oriented_JavaScript
In summary, the following simplified code block shows how we can define a new class that
extends an exising one:
function RectShape(arguments){
createjs.Container.call(this); // calling super