About initialization

For the initial values for variables, assign a default value or allow the value of undefined, as the following class example shows. When you initialize properties inline, the expression on the right side of an assignment must be a compile-time constant. That is, the expression cannot refer to anything that is set or defined at runtime. Compile-time constants include string literals, numbers, Boolean values, null, and undefined, as well as constructor functions for the following top-level classes: Array, Boolean, Number, Object, and String. This class sets the initial values of m_username and m_password to empty strings:

class User {
    private var m_username:String = "";
    private var m_password:String = "";
    function User(username:String, password:String) {
        this.m_username = username;
        this.m_password = password;
    }
}

Delete variables or make variables null when you no longer need them. Setting variables to null can still enhance performance. This process is commonly called garbage collection. Deleting variables helps optimize memory use during runtime, because unneeded assets are removed from the SWF file. It is better to delete variables than to set them to null. For more information on performance, see Optimizing your code.

For information on naming variables, see Naming variables. For more information on deleting objects, see delete statement in ActionScript 2.0 Language Reference.

One of the easiest ways to initialize code by using ActionScript 2.0 is to use classes. You can encapsulate all your initialization for an instance within the class's constructor function, or abstract it into a separate method, which you would explicitly call after the variable is created, as the following code shows:

class Product {
    function Product() {
        var prodXml:XML = new XML();
        prodXml.ignoreWhite = true;
        prodXml.onLoad = function(success:Boolean) {
            if (success) {
                trace("loaded");
            } else {
                trace("error loading XML");
            }
        };
        prodXml.load("products.xml");
    }
}

The following code could be the first function call in the application, and the only one you make for initialization. Frame 1 of a FLA file that is loading XML might use code that is similar to the following ActionScript:

if (init == undefined) {
    var prodXml:XML = new XML();
    prodXml.ignoreWhite = true;
    prodXml.onLoad = function(success:Boolean) {
        if (success) {
            trace("loaded");
        } else {
            trace("error loading XML");
        }
    };
    prodXml.load("products.xml");
    init = true;
}