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prototypeFunction

Here, the subclass and superclass names are passed in as strings, not as pointers to their constructors.

This call must come before the constructor for the given subclass.

You can also call

registerClass()

with only the first argument if the new class doesn’t inherit from

another class.

The second step is to call the

defineClass()

method inside of the constructor, passing in the name of

the class as well as a pointer to what Clary calls a

prototype function

, which is used to initialize all proper-

ties and methods for the object (more on that later). For example:

_classes.registerClass(“ClassA”);

function ClassA(color) {

_classes.defineClass(“ClassA”, prototypeFunction);

function prototypeFunction() {

//...

}

As you can see, the prototype function (aptly named

prototypeFunction()

) is located inside of the

constructor. Its main purpose is to assign all methods to the class when appropriate (it works like

dynamic prototyping in this way).

The next step (that’s three so far) is to create an

init()

method for the class. This method is responsible

for setting up all properties for the class and must accept the same arguments as the constructor itself.

By convention, the

init()

method is always called after the

defineClass()

method is called. For

example:

_classes.registerClass(“ClassA”);

function ClassA(sColor) {

_classes.defineClass(“ClassA”, prototypeFunction);

this.init(sColor);

function prototypeFunction() {

ClassA.prototype.init = function (sColor) {

this.parentMethod(“init”);

this.color = sColor;

};

}

You may have noticed a method named

parentMethod()

being called in the

init()

method. This is

the way that xbObjects allows a class to call a superclass method. The

parentMethod()

accepts any

number of arguments, but the first argument is always the name of the parent class method to call (this

argument must be a string, not a function pointer); all other arguments are passed to the superclass

method.

121

Inheritance

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