MACROMEDIA Flex Reference

Flex ActionScript Language Reference

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Acknowledgments

Project Management: Barbara Herbert, Stephen Gilson

Writing: Jody Bleyle, Mary Burger, Kim Diezel, Stephen Gilson, Stephanie Gowin, Dan Harris, Barbara Herbert, Matt Horn,

Barbara Nelson, Shirley Ong, Michael Peterson, Tim Statler

Managing Editor: Rosana Francescato

Editing: Linda Adler, Mary Ferguson, Mary Kraemer, Noreen Maher, Antonio Padial, Lisa Stanziano, Anne Szabla

Production Management: Patrice O’Neill

Media Design and Production: Adam Barnett, Christopher Basmajian, Aaron Begley, John Francis

Second Edition: November 2004

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3

CONTENTS

INTRODUCTION: Getting Started with ActionScript . . . . . . . . . . . . . . . . . . . . . . . 5

Intended audience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Using the documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Typographical conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Terms used in this document. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Additional resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

PART I: Welcome to ActionScript

CHAPTER 1: ActionScript Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Differences between ActionScript and JavaScript . . . . . . . . . . . . . . . . . . . . . . . . . 10

Unicode support for ActionScript . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

About data types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Assigning data types to elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

About variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Using operators to manipulate values in expressions . . . . . . . . . . . . . . . . . . . . . . . 31

Using condition statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Using built-in functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Creating functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

CHAPTER 2: Creating Custom Classes with ActionScript 2.0 . . . . . . . . . . . . . . . 45

Principles of object-oriented programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Using classes: a simple example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Creating and using classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Creating dynamic classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Using packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Creating and using interfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Instance and class members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Implicit getter/setter methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Understanding the classpath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Importing classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

4 Contents

CHAPTER 3: Working with External Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Sending and loading variables to and from a remote source . . . . . . . . . . . . . . . . . . 67

Sending messages to and from Flash Player . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

PART II: Reference

CHAPTER 4: About the ActionScript Language Reference . . . . . . . . . . . . . . . . . 77

Sample entry for most ActionScript elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Sample entry for classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

CHAPTER 5: ActionScript Core Language Elements. . . . . . . . . . . . . . . . . . . . . . 80

CHAPTER 6: ActionScript Core Classes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

CHAPTER 7: ActionScript for Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490

APPENDIX A: Deprecated Flash 4 operators . . . . . . . . . . . . . . . . . . . . . . . . . . . 809

APPENDIX B: Keyboard Keys and Key Code Values . . . . . . . . . . . . . . . . . . . . . 811

Letters A to Z and standard numbers 0 to 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 811

Keys on the numeric keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813

Function keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813

Other keys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817

INDEX OF LANGUAGE ELEMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823

5

INTRODUCTION

Getting Started with ActionScript

Macromedia Flex developers can use ActionScript to extend the functionality of their Flex

applications. ActionScript is an ECMAScript-based language that provides support for object-

oriented development. You are not required to use ActionScript to use Flex, but it provides flow

control and object manipulation features that are not available in strict MXML.

Intended audience

This manual assumes that you already installed Macromedia Flex and know how to use it. If you

have written programs before, ActionScript will seem familiar. But if you’re new to programming,

ActionScript isn’t hard to learn. It’s easy to start with simple commands and build more

complexity as you progress.

Using the documentation

This manual provides an overview of ActionScript syntax, information on how to use

ActionScript when working with different types of objects, and details on the syntax and usage of

every language element. The following list summarizes the contents of this manual.

• Chapter 1, “ActionScript Basics,” on page 9 describes the terminology and basic concepts used

in the rest of the manual.

• Chapter 2, “Creating Custom Classes with ActionScript 2.0,” on page 45 describes how to

create custom classes and objects for manipulating data in your applications.

• Chapter 3, “Working with External Data,” on page 67 describes how to process data from

external sources using server- or client-side scripts in your applications.

• Chapter 4, “About the ActionScript Language Reference,” on page 77 provides an overview of

the second part of the manual, which describes the elements that comprise the ActionScript

language.

• Chapter 5, “ActionScript Core Language Elements,” on page 80 explains all of the elements of

the ActionScript language that are not related to a particular class or to a particular

Macromedia product.

• Chapter 6, “ActionScript Core Classes,” on page 232 documents all of the classes of the

ActionScript language that are not related to a particular Macromedia product.

6 Introduction: Getting Started with ActionScript

• Chapter 7, “ActionScript for Flash,” on page 490 describe functions, properties, and classes of

Macromedia Flash Player that you can use in a Macromedia Flex application, if appropriate.

• Appendix A, “Deprecated Flash 4 operators,” on page 809 lists all the ActionScript operators

and their associativity.

• Appendix B, “Keyboard Keys and Key Code Values,” on page 811 lists all the keys on a

standard keyboard and the corresponding ASCII key code values that are used to identify the

keys in ActionScript.

Typographical conventions

The following typographical conventions are used in this manual:

• Code font indicates ActionScript code.

• Code font italic indicates an element, such as an ActionScript parameter or object name,

that you replace with your own text when writing a script.

Terms used in this document

The following terms are used in this manual:

• You refers to the developer who is writing a script or application.

• The user refers to the person who is running your scripts and applications.

• Compile time is the time at which you publish, export, test, or debug your document.

• Runtime is the time at which your script is running in Flash Player.

ActionScript terms such as method and object are defined in Chapter 1, “ActionScript Basics,” on

page 9.

Additional resources

Specific documentation about Macromedia Flash and related products is available separately.

• For information about creating communication applications with Flash Communication

Server, see Developing Communications Applications and Managing Flash Communication Server.

• For information about building Flex applications, see Developing Flex Applications.

The Macromedia DevNet website (www.macromedia.com/devnet) is updated regularly with the

latest information on Flash, plus advice from expert users, advanced topics, examples, tips, and

other updates. Check the website often for the latest news on Flash and how to get the most out

of the program.

The Macromedia Flash Support Center (www.macromedia.com/support/flash) provides

TechNotes, documentation updates, and links to additional resources in the Flash community.

PART I

Welcome to ActionScript

This part includes information on using the ActionScript language. For information on the

classes and language elements you can use in your scripts, see Part II, “Reference.”

Chapter 1: ActionScript Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Chapter 2: Creating Custom Classes with ActionScript 2.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Chapter 3: Working with External Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

PART I

9

CHAPTER 1

ActionScript Basics

ActionScript has rules of grammar and punctuation that determine which characters and words

are used to create meaning and in which order they can be written. For example, in English, a

period ends a sentence; in ActionScript, a semicolon ends a statement.

The general rules described in this section apply to all ActionScript. Most ActionScript terms also

have individual requirements; for the rules for a specific term, see its entry in Part II, “Reference.”

Applying the basics of ActionScript in a way that creates elegant programs can be a challenge for

users who are new to ActionScript.

This section contains the following topics:

• “Differences between ActionScript and JavaScript” on page 10

• “Terminology” on page 11

• “Syntax” on page 13

• “About data types” on page 18

• “Assigning data types to elements” on page 23

• “About variables” on page 27

• “Using operators to manipulate values in expressions” on page 31

• “Using condition statements” on page 39

• “Using built-in functions” on page 41

• “Creating functions” on page 41

10 Chapter 1: ActionScript Basics

Differences between ActionScript and JavaScript

ActionScript is similar to the core JavaScript programming language. You don’t need to know

JavaScript to use and learn ActionScript; however, if you know JavaScript, ActionScript will

seem familiar.

This manual does not attempt to teach general programming. There are many resources that

provide more information about general programming concepts and the JavaScript language.

• The European Computers Manufacturers Association (ECMA) document ECMA-262 is

derived from JavaScript and serves as the international standard for the JavaScript language.

ActionScript is based on the ECMA-262 specification. For more information, see www.ecma-

international.org/publications/standards/Ecma-262.htm.

• Netscape DevEdge Online has a JavaScript Developer Central site (http://

developer.netscape.com/tech/javascript/index.html) that contains documentation and articles

useful for understanding ActionScript. The most valuable resource is the Core JavaScript Guide.

• The Java Technology site has tutorials on object-oriented programming (http://java.sun.com/

docs/books/tutorial/java/index.html) that are targeted for the Java language but are useful for

understanding concepts that you can apply to ActionScript.

Some of the differences between ActionScript and JavaScript are described in the following list:

• ActionScript does not support browser-specific objects such as Document, Window,

and Anchor.

• ActionScript does not completely support all the JavaScript built-in objects.

• ActionScript does not support some JavaScript syntax constructs, such as statement labels.

• In ActionScript, the eval() function can perform only variable references.

• ActionScript2.0 supports several features that are not in the ECMA-262 specification, such as

classes and strong typing. Many of these features are modeled after the ECMAScript 4 Draft

Proposal currently in development by ECMA TC39-TG1 (see www.mozilla.org/js/language/

es4/index.html), the standards committee in charge of the evolution of the ECMA-262

specification.

• ActionScript does not support regular expressions using the RegExp object. However,

Macromedia Central does support the RegExp object.

Unicode support for ActionScript

Macromedia Flex supports Unicode text encoding for ActionScript. This means that you can

include text in different languages in an ActionScript file. For example, you can include text in

English, Japanese, and French in the same file. For more information on Unicode support in Flex,

see “Using MXML” in Developing Flex Applications.

Terminology 11

Terminology

As with all scripting languages, ActionScript uses its own terminology. The following list provides

an introduction to important ActionScript terms:

Boolean is a true or false value.

Classes are data types that you can create to define a new type of object. To define a class,

you use the

class keyword in a script file.

Constants are elements that don’t change. For example, the constant Key.TAB always has the

same meaning: it indicates the Tab key on a keyboard. Constants are useful for comparing values.

Constructors are functions that you use to define (initialize) the properties and methods of a

class. By definition, constructors are functions within a class definition that have the same name

as the class. For example, the following code defines a Circle class and implements a

constructor function:

// file Circle.as

class Circle {

private var circumference:Number;

// constructor

function Circle(radius:Number){

this.circumference = 2 * Math.PI * radius;

}

The term constructor is also used when you create (instantiate) an object based on a particular

class. The following statements are calls to the constructor functions for the built-in Array class

and the custom Circle class:

var my_array:Array = new Array();

var my_circle:Circle = new Circle(9);

Data types

describe the kind of information a variable or ActionScript element can contain. The

built-in ActionScript data types are String, Number, Boolean, Object, MovieClip, Function, null,

and undefined. For more information, see “About data types” on page 18.

Events are actions that occur while a SWF file is playing. For example, different events are

generated when a movie clip loads, the user clicks a button or movie clip, or the user types on

the keyboard.

Event handlers are special actions that manage events such as mouseDown or load. There are two

kinds of ActionScript event handlers: event handler methods and event listeners. Some

commands can be used both as event handlers and as event listeners and are included in both

subcategories. For more information on event management, see Developing Flex Applications.

Expressions are any legal combination of ActionScript symbols that represent a value. An

expression consists of operators and operands. For example, in the expression

x + 2, x and 2 are

operands and

+ is an operator.

Functions are blocks of reusable code that can be passed parameters and can return a value. For

more information, see “Creating functions” on page 41.

12 Chapter 1: ActionScript Basics

Identifiers are names used to indicate a variable, property, object, function, or method. The first

character must be a letter, underscore (

_), or dollar sign ($). Each subsequent character must be a

letter, number, underscore, or dollar sign. For example,

firstName is the name of a variable.

Instances are objects that contain all the properties and methods of a particular class. For

example, all arrays are instances of the Array class, so you can use any of the methods or properties

of the Array class with any array instance.

Instance names are unique names that let you target instances you create. For example, in the

following code, “names” and “studentName” are instance names for two objects, an array and a

string:

var names:Array = new Array();

var studentName:String = new String();

Keywords

are reserved words that have special meaning. For example, var is a keyword used to

declare local variables. You cannot use a keyword as an identifier. For example,

var is not a legal

variable name. For a list of keywords, see “Keywords and reserved words” on page 17.

Methods are functions associated with a class. For example, sortOn() is a built-in method

associated with the Array class. You can also create functions that act as methods, either for

objects based on built-in classes or for objects based on classes that you create. For example, in the

following code,

clear() becomes a method of a controller object that you have previously

defined:

function reset(){

this.x_pos = 0;

this.y_pos = 0;

}

controller.clear = reset;

controller.clear();

The following examples show how you create methods of a class:

//ActionScript 1 example

A = new Object();

A.prototype.myMethod = function() {

trace("myMethod");

}

//ActionScript 2 example

class B {

function myMethod() {

trace("myMethod");

}

Objects

are collections of properties and methods; each object has its own name and is an

instance of a particular class. Built-in objects are predefined in the ActionScript language. For

example, the built-in Date class provides information from the system clock.

Operators are terms that calculate a new value from one or more values. For example, the

addition (

+) operator adds two or more values together to produce a new value. The values that

operators manipulate are called operands.

Syntax 13

Parameters (also called arguments) are placeholders that let you pass values to functions.

For example, the following

welcome() function uses two values it receives in the parameters

firstName and hobby:

function welcome(firstName:String, hobby:String):String {

var welcomeText:String = "Hello, " + firstName + ". I see you enjoy " + hobby

+".";

return welcomeText;

}

Packages

are directories that contain one or more class files and reside in a designated classpath

directory (see “Understanding the classpath” on page 64).

Properties are attributes that define an object. For example, length is a property of all arrays that

specifies the number of elements in the array.

Statements are language elements that perform or specify an action. For example, the return

statement returns a result as a value of the function in which it executes. The

if statement

evaluates a condition to determine the next action that should be taken. The

switch statement

creates a branching structure for ActionScript statements.

Target paths are hierarchical addresses of movie clip instance names, variables, and objects in a

SWF file. You can use a target path to direct an action at a movie clip or to get or set the value of

a variable or property. For example, the following statement is the target path to the

volume

property of the object named

stereoControl:

stereoControl.volume

Variables

are identifiers that hold values of any data type. Variables can be created, changed, and

updated. The values they store can be retrieved for use in scripts. In the following example, the

identifiers on the left side of the equal signs are variables:

var x:Number = 5;

var name:String = "Lolo";

var c_color:Color = new Color(mcinstanceName);

For more information on variables, see “About variables” on page 27.

Syntax

As with all scripting languages, ActionScript has syntax rules that you must follow to create scripts

that can compile and run correctly. This section describes the elements that comprise

ActionScript syntax:

• “Case sensitivity” on page 14

• “Dot syntax” on page 14

• “Curly braces” on page 15

• “Semicolons” on page 15

• “Parentheses” on page 16

• “Comments” on page 16

14 Chapter 1: ActionScript Basics

• “Keywords and reserved words” on page 17

• “Constants” on page 18

Case sensitivity

In a case-sensitive programming language, variable names that differ only in case (

book and Book)

are considered different from each other. Therefore, it’s good practice to follow consistent

capitalization conventions, such as those used in this manual, to make it easy to identify names of

functions and variables in ActionScript code.

Keywords, class names, variables, method names, and so on are case sensitive. For example:

// Sets properties of two different objects

cat.hilite = true;

CAT.hilite = true;

// Creates three different variables

var myVar:Number=10;

var myvar:Number=10;

var mYvAr:Number=10;

This change also affects external variables loaded with LoadVars.load().

Case-sensitivity is implemented for external scripts, such as class files, scripts that you import

using the

#include command, and scripts in a FLA file. If you encounter runtime errors and are

exporting to more than one version of Flash Player, you should review both external script files

and scripts in FLA files to confirm that you used consistent capitalization.

Case-sensitivity is implemented on a per-movie basis. If a strict Flash Player 7 application calls a

non-strict Flash Player 6 movie, ActionScript executed in the latter movie is non-strict. For

example, if you use

loadMovie() to load a Flash Player 6 SWF into a Flash Player 7 SWF, the

version 6 SWF remains case-insensitive, while the version 7 SWF is treated as case-sensitive.

Dot syntax

In ActionScript, a dot (

.) is used to access properties or methods belonging to an object. It is also

used to identify the target path to a variable, function, or object. A dot syntax expression begins

with the name of the object followed by a dot and ends with the element you want to specify.

For example, the

_x movie clip property indicates a movie clip’s x axis position. The expression

ball_mc._x refers to the _x property of the movie clip instance ball_mc.

Expressing a method of an object follows the same pattern. For example, the

bounce() method of

the

ball object would be called as follows:

ball.bounce();

For more information, see _parent, _global object, and _root.

Syntax 15

Curly braces

ActionScript event handlers, class definitions, and functions are grouped together into blocks

with curly braces (

{}). You can put the opening brace on the same line as your declaration or on

the next line, as shown in the following examples. To make your code easier to read, it’s a good

idea to choose one format and use it consistently. The following examples show the opening brace

on same line as the declaration:

// Event handler

my_btn.onRelease = function() {

var myDate:Date = new Date();

var currentMonth:Number = myDate.getMonth();

};

// Class Circle.as

class Circle(radius) {

}

// Function

circleArea = function(radius:Number){

return radius * radius * Math.PI;

}

The following examples show code with opening brace on the next line:

//Event handler

my_btn.onRelease = function()

{

var myDate:Date = new Date();

var currentMonth:Number = myDate.getMonth();

};

//Class Square.as

class Square(side)

{

}

//Function

squareArea = function(side:Number)

{

return side * side;

}

Semicolons

An ActionScript statement is terminated with a semicolon (

;), as shown in the following

examples:

var column:Number = passedDate.getDay();

var row:Number = 0;

If you omit the terminating semicolon, Flash still compiles your script successfully. However, it is

good scripting practice to use semicolons because it makes your code more readable.

16 Chapter 1: ActionScript Basics

Semicolons are required within for loops, as shown in the following example:

//For loop that adds numbers 1-10

var sum:Number = 0;

for (var i=1; i<=10; i++) {

sum += i;

}

Parentheses

When you define a function, place any parameters inside parentheses [()]:

function myFunction (name:String, age:Number, reader:Boolean){

// your code here

}

When you call a function, include any parameters passed to the function in parentheses, as

shown in the following example:

myFunction ("Steve", 10, true);

You can also use parentheses to override the ActionScript order of precedence or to make your

ActionScript statements easier to read. (See “Operator precedence and associativity” on page 32.)

You also use parentheses to evaluate an expression on the left side of a dot (.) in dot syntax. For

example, in the following statement, the parentheses cause

new Color(this) to evaluate and

create a Color object:

(new Color(this)).setRGB(0xffffff);

If you don’t use parentheses, you must add a statement to evaluate the expression, as shown in the

following example:

myColor = new Color(this);

myColor.setRGB(0xffffff);

Comments

Using comments to add notes to scripts is highly recommended. Comments are useful for

tracking what you intended and for passing information to other developers if you work in a

collaborative environment or are providing samples. Even a simple script is easier to understand if

you make notes as you create it.

As shown in the following example, to indicate that a line or portion of a line is a comment,

precede the comment with two forward slashes (

//):

my_btn.onRelease = function() {

// create new Date object

var myDate:Date = new Date();

var currentMonth:Number = myDate.getMonth();

// convert month number to month name

var monthName:String = calcMonth(currentMonth);

var year:Number = myDate.getFullYear();

var currentDate:Number = myDate.getDate();

};

Syntax 17

Comments can be any length without affecting the size of the exported file, and they do not need

to follow rules for ActionScript syntax or keywords.

To create a comment block, place

/* at the beginning of the commented lines and */ at the end.

This technique lets you create lengthy comments without adding // at the beginning of each line.

By placing large chunks of script in a comment block, called commenting out a portion of your

script, you can test specific parts of a script. For example, when the following script runs, none of

the code in the comment block is executed:

// The following code runs

var x:Number = 15;

var y:Number = 20;

// The following code doesn’t run

/*

// create new Date object

var myDate:Date = new Date();

var currentMonth:Number = myDate.getMonth();

// convert month number to month name

var monthName:String = calcMonth(currentMonth);

var year:Number = myDate.getFullYear();

var currentDate:Number = myDate.getDate();}

*/

// The code below runs

var name:String = "My name is";

var age:Number = 20;

Keywords and reserved words

ActionScript reserves words for specific use within the language, so you can’t use them

as identifiers, such as variable, function, or label names. The following table lists all

ActionScript keywords:

break case class continue

default delete dynamic else

extends for function get

if implements import in

instanceof interface intrinsic new

private public return set

static switch this typeof

var void while with

18 Chapter 1: ActionScript Basics

Constants

A constant is a property whose value never changes. ActionScript contains predefined constants.

For example, the constants

BACKSPACE, ENTER, SPACE, and TAB are properties of the Key object

and refer to keyboard keys. To test whether the user is pressing the Enter key, you could use the

following statement:

if(Key.getCode() == Key.ENTER) {

alert = "Are you ready to play?";

control_mc.gotoAndStop(5);

}

Flash does not enforce constants; that is, you can’t define your own constants.

About data types

A data type describes a piece of data and the kinds of operations that can be performed on it. That

data is stored in a variable. You use data types when creating variables, object instances, and

function definitions.

ActionScript has the following basic data types that you will probably use frequently in your

applications:

• “String data type” on page 19

• “Number data type” on page 19

• “Boolean data type” on page 20

• “Object data type” on page 21

• “Null data type” on page 22

• “Undefined data type” on page 23

• “Void data type” on page 23

ActionScript also has built-in classes, such as Array and Date, that can be considered complex

data types. If you are an advanced developer, you might create custom classes. Any class that you

define using the

class declaration is also considered a data type.

Variables containing primitive data types behave differently in certain situations than those

containing reference types. (See “Using variables in a program” on page 29.) There are also two

special data types: null and undefined.

When you debug scripts, you might need to determine the data type of an expression or variable

to understand why it is behaving a certain way. You can do this with the

instanceof operator

(see “Determining an item’s data type” on page 26).

You can convert one data type to another using one of the following conversion functions:

Array(), Boolean(), Number(), Object(), String().

In ActionScript 2.0, you can assign data types to variables when you initialize them. The data

types you assign can be any of the built-in types or can represent a custom class that you’ve

created. For more information, see “Strict data typing” on page 24.

For more information on Flex data types, see Developing Flex Applications.

About data types 19

String data type

A string is a sequence of characters such as letters, numbers, and punctuation marks. You enter

strings in an ActionScript statement by enclosing them in single (') or double (") quotation

marks.

A common way that you use the string type is to assign a string to a variable. For example, in the

following statement,

"L7" is a string assigned to the variable favoriteBand_str:

var favoriteBand_str:String = "L7";

You can use the addition (+) operator to concatenate, or join, two strings. ActionScript treats

spaces at the beginning or end of a string as a literal part of the string. The following expression

includes a space after the comma:

var greeting_str:String = "Welcome, " + firstName;

To include a quotation mark in a string, precede it with a backslash character (\). This is called

escaping a character. There are other characters that cannot be represented in ActionScript except

by special escape sequences. The following table provides all the ActionScript escape characters:

Strings in ActionScript are immutable, the same as Java. Any operation that modifies a string

returns a new string.

The String class is a built-in ActionScript class.

Number data type

The number data type is a double-precision floating-point number. The minimum value of a

number object is approximately 5e-324. The maximum is approximately 1.79E+308.

You can manipulate numbers using the arithmetic operators addition (

+), subtraction (-),

multiplication (

*), division (/), modulo (%), increment (++), and decrement (--). For more

information, see “Numeric operators” on page 33.

Escape sequence Character

\b

Backspace character (ASCII 8)

\f

Form-feed character (ASCII 12)

\n

Line-feed character (ASCII 10)

\r

Carriage return character (ASCII 13)

\t

Tab character (ASCII 9)

\"

Double quotation mark

\'

Single quotation mark

\\

Backslash

\000 - \377

A byte specified in octal

\x00 - \xFF

A byte specified in hexadecimal

\u0000 - \uFFFF

A 16-bit Unicode character specified in hexadecimal

20 Chapter 1: ActionScript Basics

You can also use methods of the built-in Math and Number classes to manipulate numbers. For

more information on the methods and properties of these classes, see the “Math class” and

“Number class” entries.

The following example uses the

sqrt() (square root) method of the Math class to return the

square root of the number 100:

Math.sqrt(100);

The following example traces a random integer between 10 and 17 (inclusive):

var bottles:Number = 0;

bottles = 10 + Math.floor(Math.random()*7);

trace("There are " + bottles + " bottles");

The following example finds the percent of the intro_mc movie clip loaded and represents it as

an integer:

var percentLoaded:Number = Math.round((intro_mc.getBytesLoaded()/

intro_mc.getBytesTotal())*100);

Boolean data type

A Boolean value is one that is either

true or false. ActionScript also converts the values true

and

false to 1 and 0 when appropriate. Boolean values are most often used with logical

operators in ActionScript statements that make comparisons to control the flow of a script.

The following example checks that users enter values into two TextInput component instances.

Two Boolean variables are created,

userNameEntered and isPasswordCorrect, and if both

variables evaluate to

true, a welcome message is assigned to the titleMessage String variable.

//Add two TextInput components and one Button component on the Stage

//Strict data type the three component instances

var userName_ti:mx.controls.TextInput;

var password_ti:mx.controls.TextInput;

var submit_button:mx.controls.Button;

//Create a listener object, which is used with the Button component

//When the Button is clicked, checks for a user name and password

var btnListener:Object = new Object();

btnListener.click = function(evt:Object) {

//checks that the user enters at least one character in the TextInput

//instances and returns a Boolean true/false.

var userNameEntered:Boolean = (userName_ti.text.length>0);

var isPasswordCorrect:Boolean = (password_ti.text == "vertigo");

if (userNameEntered && isPasswordCorrect) {

var titleMessage:String = "Welcome "+userName_ti.text+"!";

}

};

submit_button.addEventListener("click", btnListener);

For more information, see “Using built-in functions” on page 41 and “Logical operators”

on page 36.

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