Defining Classes
Lets get back to defining the House class. Starting with the class constructor we have the following.

House = function(){

this.floors = 4;

this.siding = "Red";

};

This is the definition for creating house instances which, by default, will each be created with two properties, floors and siding with the values 4 and “Red” respectively. As classes go, this one’s fairly simple. In fact it’s simply constructor for creating instances that serve as containers for 2 pieces of information. Some functionality can be added to house instances by adding a simple method in the function constructor. Then, each house instance will have access to this method much like each array has access to its method push.

House = function(){

this.floors = 4;

this.siding = "Red";

this.outputSiding = function(){

trace(this.siding);

};

};

 

// create an instance of the House class

myHouse = new House();

myHouse.outputSiding(); // traces "Red"

In these kinds of methods, when defined in the constructor like this (which isn’t common – something to be discussed later), be sure to assign the function to the this reference as this is the object being created. That is, after all, the object you want to use the method with. Inside the method function definition, this will also still correctly reference the new object instance as the this object is the object doing the calling of the method.

Like any other function, class constructors can also take function parameters so that you can send values into the constructor call helping you uniquely define each instance created. For example, we can make the siding of the house class customizable by passing it in as a parameter in the function call.

// class definition

House = function(siding){

this.floors = 4;

this.siding = siding;

this.outputSiding = function(){

trace(this.siding);

};

};

 

// create an instance of the House class to have blue siding

myHouse = new House("Blue");

Here, myHouse has a siding value of "Blue." Note that Flash is able to distinguish the difference of the instance’s siding variable and the passed siding variable through the use of this. The this keyword indicates the difference between values in the created object and values from the local scope of the function (or the timeline even). Here, siding was used for both the argument variable and and instance’s property though it is not necessary. Feel free to use separate variable names for each if you please.

If now, say you want the siding to be optional, you could also allow for that in the constructor function definition. You would just have to check to see if a siding value was passed. If it was passed, assign the siding value to that passed siding, otherwise use a default as defined by you. This version of the House class assigns the siding of the new House instance to be the passed siding value if it was passed and is not undefined. Otherwise, it sets the siding to be "Red."

// class definition

House = function(siding){

this.floors = 4;

if (siding != undefined){

this.siding = siding;

}else{

this.siding = "Red";

}

this.outputSiding = function(){

trace(this.siding);

};

};

 

// create an instance of the House class to have blue siding

myHouse = new House("Blue");

// create an instance of the House class to have red siding

myHouse = new House();

Don't, however, feel obligated to make all properties used in your constructors optional this way. Often these passed values are required. Besides, it's less work on you having to check to see whether they're defined or not to see whether they need to be assigned which value, and who needs that? For the House class constructor, we can leave siding optional, but for the floors property, we can make that a required parameter when creating a new house instance. Not every (if any) house made needs to be a whopping 4 stories high. Users of the House constructor will just need to know to make sure they specify how many floors they want their house to be when they make a new House.

// revised class definition

House = function(floors, siding){

this.floors = floors;

if (siding != undefined){

this.siding = siding;

}else{

this.siding = "Red";

}

this.outputSiding = function(){

trace(this.siding);

};

};

And with that you have a fairly complete, though simple, class definition complete with properties and a method which will be copied into each instance of a house created.

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