Macromedia FLASH MX USING ACTIONSCRIPT IN FLASH User Manual

Using ActionScript in Flash

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Acknowledgments

Director: Erick Vera

Project Management: Julee Burdekin, Erick Vera

Writing: Jay Armstrong, Jody Bleyle, Mary Burger, Francis Cheng, Jen deHaan, Stephanie Gowin, Phillip Heinz, Shimul Rahim, Samuel R. Neff

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: June 2004

Macromedia, Inc. 600 Townsend St.

San Francisco, CA 94103

INTRODUCTION: Getting Started with ActionScript . . . . . . . . . . . . . . . . . . . . . . . 7

Intended audience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

System requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Using the documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Typographical conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Terms used in this document. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Additional resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

CHAPTER 1: What’s New in Flash MX 2004 ActionScript. . . . . . . . . . . . . . . . . . 11

Updating Flash XML files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

New and changed language elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

New security model and legacy SWF files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Porting existing scripts to Flash Player 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

ActionScript editor changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Debugging changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

New object-oriented programming model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

CHAPTER 2: ActionScript Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Differences between ActionScript and JavaScript . . . . . . . . . . . . . . . . . . . . . . . . . 24

Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

About data types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Assigning data types to elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

About variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Using operators to manipulate values in expressions . . . . . . . . . . . . . . . . . . . . . . . 49

Specifying an object’s path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Using condition statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Using built-in functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Creating functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

CHAPTER 3: Using Best Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Working with FLA files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

General coding conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

ActionScript coding standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Using classes and ActionScript 2.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Behaviors conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Screens conventions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Video conventions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Performance and Flash Player . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

Guidelines for Flash applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Projects and version control guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Guidelines for accessibility in Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Advertising with Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

CHAPTER 4: Writing and Debugging Scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

Controlling when ActionScript runs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Using the Actions panel and Script window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Using the ActionScript editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Unicode support for ActionScript . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

Debugging your scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Using the Output panel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

Updating Flash Player for testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

CHAPTER 5: Handling Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Using event handler methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Using event listeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Using button and movie clip event handlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

Broadcasting events from component instances . . . . . . . . . . . . . . . . . . . . . . . . . . 173

Creating movie clips with button states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

Event handler scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

Scope of the this keyword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

CHAPTER 6: Creating Interaction with ActionScript . . . . . . . . . . . . . . . . . . . . . 179

About events and interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

Controlling SWF file playback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

Creating interactivity and visual effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

Deconstructing a sample script . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

CHAPTER 7: Using the Built-In Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

About classes and instances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Overview of built-in classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

CHAPTER 8: Working with Movie Clips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

About controlling movie clips with ActionScript . . . . . . . . . . . . . . . . . . . . . . . . . 205

Calling multiple methods on a single movie clip . . . . . . . . . . . . . . . . . . . . . . . . . 206

Loading and unloading additional SWF files. . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

Specifying a root Timeline for loaded SWF files . . . . . . . . . . . . . . . . . . . . . . . . . 208

Loading JPEG files into movie clips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

Changing movie clip position and appearance. . . . . . . . . . . . . . . . . . . . . . . . . . . 209

Dragging movie clips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

Creating movie clips at runtime. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

4 Contents

Adding parameters to dynamically created movie clips . . . . . . . . . . . . . . . . . . . . 213

Managing movie clip depths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

Drawing shapes with ActionScript. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

Using movie clips as masks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217

About masking device fonts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Handling movie clip events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Assigning a class to a movie clip symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Initializing class properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

CHAPTER 9: Working with Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

Using the TextField class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

Creating text fields at runtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

Using the TextFormat class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

Formatting text with Cascading Style Sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

Using HTML-formatted text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

Creating scrolling text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

CHAPTER 10: Creating Custom Classes with ActionScript 2.0 . . . . . . . . . . . . . 247

Principles of object-oriented programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248

Using classes: a simple example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250

Creating and using classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

Creating dynamic classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

Using packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260

Creating and using interfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

Instance and class members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263

Implicit getter/setter methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

Understanding the classpath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268

Importing classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

Compiling and exporting classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

Excluding classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

CHAPTER 11: Working with External Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

Sending and loading variables to and from a remote source. . . . . . . . . . . . . . . . . 275

Sending messages to and from Flash Player . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

Flash Player security features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

CHAPTER 12: Working with External Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

Overview of loading external media. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

Loading external SWF and JPEG files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296

Loading external MP3 files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

Reading ID3 tags in MP3 files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

Playing back external FLV files dynamically . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299

Preloading external media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

Contents 5

APPENDIX A: Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305

APPENDIX B: Deprecated Flash 4 operators . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

APPENDIX C: Keyboard Keys and Key Code Values . . . . . . . . . . . . . . . . . . . . . 313

Keys on the numeric keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

Function keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

Other keys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

APPENDIX D: Writing Scripts for Earlier Versions of Flash Player . . . . . . . . . . . 319

About targeting older versions of Flash Player . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

Using Flash MX 2004 to create content for Flash Player 4. . . . . . . . . . . . . . . . . . 320

APPENDIX E: Object-Oriented Programming with ActionScript 1 . . . . . . . . . . . 323

About ActionScript 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

6 Contents

INTRODUCTION

Getting Started with ActionScript

Macromedia Flash MX 2004 and Macromedia Flash MX Professional 2004 are the professional standard authoring tools for producing high-impact web experiences. ActionScript is the language you use to add interactivity to a Flash applications, whether your applications are simple animated movies or more complex rich Internet applications. You don’t have to use ActionScript to use Flash, but if you want to provide basic or complex user interactivity, work with objects other than those built into Flash (such as buttons and movie clips), or otherwise turn a SWF file into a more robust user experience, you’ll probably want to use ActionScript.

Intended audience

This manual assumes that you have already installed Flash MX 2004 or Flash MX Professional 2004 and know how to use it. You should know how to place objects on the Stage and manipulate them in the Flash authoring environment. 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.

System requirements

ActionScript does not have any system requirements in addition to Flash MX 2004 or Flash MX Professional 2004. To use ActionScript 2.0, you must use Flash MX 2004.

The documentation assumes that you are using the default publishing settings for your Flash files: Flash Player 7 and ActionScript 2.0. If you change either of these settings, explanations and code samples shown in the documentation may not work correctly. If you develop applications for earlier versions of Flash Player, see “Porting existing scripts to Flash Player 7” on page 13 or

Appendix D, “Writing Scripts for Earlier Versions of Flash Player,” on page 319.

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, “What’s New in Flash MX 2004 ActionScript,” on page 11 describes features that

are new in ActionScript, changes to the compiler and debugger, and the new programming model for the ActionScript 2.0 language.

• Chapter 2, “ActionScript Basics,” on page 23 describes the terminology and basic concepts

used in the rest of the manual.

• Chapter 3, “Using Best Practices,” on page 65 helps explain the best practices for using Flash

and writing ActionScript.

• Chapter 4, “Writing and Debugging Scripts,” on page 139 describes the ActionScript editor

and debugger within Flash that makes it easier to write code.

• Chapter 5, “Handling Events,” on page 167 discusses a few different ways to handle events:

event handler methods, event listeners, and button and movie clip event handlers.

• Chapter 6, “Creating Interaction with ActionScript,” on page 179 describes some simple ways

in which you can create more interactive applications, including controlling when SWF files play, creating custom pointers, and creating sound controls.

• Chapter 7, “Using the Built-In Classes,” on page 197 lists the built-in classes in ActionScript

and provides a brief overview of how you use them to access powerful features in ActionScript.

• Chapter 8, “Working with Movie Clips,” on page 205 describes movie clips and the

ActionScript you can use to control them.

• Chapter 9, “Working with Text,” on page 221 describes the different ways you can control text

in Flash and include information on text formatting.

• Chapter 10, “Creating Custom Classes with ActionScript 2.0,” on page 247 describes how to

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

• Chapter 11, “Working with External Data,” on page 275 describes how to process data from

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

• Chapter 12, “Working with External Media,” on page 295 describes how to import external

media files such as JPEG, MP3, and other SWF files in your Flash applications.

• Appendix A, “Error Messages,” on page 305 contains a list of error messages that the Flash

compiler can generate.

• Appendix B, “Deprecated Flash 4 operators,” on page 311 lists all the ActionScript operators

and their associativity.

• Appendix C, “Keyboard Keys and Key Code Values,” on page 313 lists all the keys on a

standard keyboard and the corresponding ASCII key code values that are used to identify the keys in ActionScript.

• Appendix D, “Writing Scripts for Earlier Versions of Flash Player,” on page 319 provides

guidelines to help you write scripts that are syntactically correct for the player version you are targeting.

• Appendix E, “Object-Oriented Programming with ActionScript 1” provides information on

using the ActionScript 1 object model to write scripts.

This manual explains how to use the ActionScript language. For information on the language elements themselves, see ActionScript Language Reference Help.

8 Introduction: Getting Started with ActionScript

Before writing your own scripts, you should complete the lessons “Write Scripts with ActionScript” and “Create a Form with Conditional Logic and Send Data,” which provide a hands-on introduction to working with ActionScript. To find these lessons, select Help > How Do I > Quick Tasks.

When you find information about a certain command you want to use, you can look up its entry in ActionScript Language Reference Help.

When you find information about a certain command you want to use, you can look up its entry in Flash ActionScript Language Reference.

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 2, “ActionScript Basics,” on

page 23.

Additional resources

Specific documentation about Flash and related products is available separately.

• For information about the elements that comprise the ActionScript language, see ActionScript

Language Reference Help.

• For information about working in the Flash authoring environment, see Using Flash Help.

• For information about working with components, see Using Components Help.

• For information about creating communication applications with Flash Communication

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

• For information about accessing web services with Flash applications, see Using Flash Remoting.

You can find application FLA files that use common Flash functionality installed with Flash. These applications were designed to introduce new Flash developers to the capabilities of Flash applications as well as show advanced developers how Flash features work in context. On Windows, you can find the applications in \Program Files\Macromedia\Flash MX 2004\ Examples. On the Macintosh, you can find the applications in HD/Applications/Macromedia Flash MX 2004/Examples.

Additional resources 9

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.

10 Introduction: Getting Started with ActionScript

CHAPTER 1

What’s New in Flash MX 2004 ActionScript

Macromedia Flash MX 2004 and Macromedia Flash MX Professional 2004 provide several enhancements that make it easy for you to write robust scripts using the ActionScript language. The new features, which are discussed in this chapter, include new language elements, improved editing and debugging tools (see “ActionScript editor changes” on page 20 and “Debugging

changes” on page 21), and the introduction of a more object-oriented programming model (see “New object-oriented programming model” on page 21).

This chapter also contains an extensive section that you should read carefully if you plan to publish any of your existing Flash MX or earlier files to Flash Player 7 (see “Porting existing

scripts to Flash Player 7” on page 13).

Updating Flash XML files

It is important that you always have the latest Flash XML files installed. Macromedia sometimes introduces features in dot releases (minor releases) of Flash Player. When such a release is available, you should update your version of Flash to get the latest XML files. Otherwise, the Flash MX 2004 compiler might generate errors if you use new properties or methods that were unavailable in the version of Flash Player that came with your Flash installation.

For example, Flash Player 7 (7.0.19.0) contained a new method for the System object,

System.security.loadPolicyFile. To access this method, you must use the Player Updater

installer to update all the Flash Players that are installed with Flash. Otherwise, the Flash MX 2004 compiler displays errors.

Remember that you can install a Player Updater that is one or more major versions ahead of your version of Flash. By doing this, you will get the XML files that you need but shouldn’t have any compiler errors when you publish to older versions of Flash Player. Sometimes new methods or properties are available to older versions, and having the latest XML files minimizes the compiler errors you get when you try to access older methods or properties.

New and changed language elements

This section describes the ActionScript language elements that are new or changed in Flash MX

2004. To use any of these elements in your scripts, you must target Flash Player 7 (the default) when you publish your documents.

• The Array.sort() and Array.sortOn() methods let you add parameters to specify

additional sorting options, such as ascending and descending sorting, whether to consider casesensitivity when sorting, and so on.

• The Button.menu, MovieClip.menu, and TextField.menu properties work with the new

ContextMenu and ContextMenuItem classes to let you associate context menu items with Button, MovieClip, or TextField objects.

• The “ContextMenu class” and “ContextMenuItem class” let you customize the context menu

that appears when a user right-clicks (Windows) or Control-clicks (Macintosh) in Flash Player.

• The “Error class” and the throw and try..catch..finally commands let you implement

more robust exception handling.

• The LoadVars.addRequestHeader() and XML.addRequestHeader() methods add or change

HTTP request headers (such as

Content-Type or SOAPAction) sent with POST actions.

• The MMExecute() function lets you issue Flash JavaScript API commands from ActionScript.

• The Mouse.onMouseWheel event listener is generated when the user scrolls using the mouse

wheel (Windows only).

• The MovieClip.getNextHighestDepth() method lets you create MovieClip instances at

runtime and be guaranteed that their objects render in front of the other objects in a parent movie clip’s z-order space.

• The MovieClip.getInstanceAtDepth() method lets you access dynamically created

MovieClip instances using the depth as a search index.

• The MovieClip.getSWFVersion() method lets you determine which version of Flash Player

is supported by a loaded SWF file.

• The MovieClip.getTextSnapshot() method and the “TextSnapshot object” let you work

with text that is in static text fields in a movie clip.

• The MovieClip._lockroot property lets you specify that a movie clip will act as _root for

any movie clips loaded into it or that the meaning of movie clip is loaded into another movie clip.

_root in a movie clip won’t change if that

• The “MovieClipLoader class” lets you monitor the progress of files as they are loaded into

movie clips.

• The “NetConnection class” and “NetStream class” let you stream local Flash video (FLV) files.

• The “PrintJob class” gives you (and the user) more control over printing from Flash Player.

• The Sound.onID3 event handler provides access to ID3 data associated with a Sound object

that contains an MP3 file.

• The Sound.id3 property provides access to the metadata that is part of an MP3 file.

• The “System class” has new objects and methods, and the “System.capabilities object” has

several new properties.

12 Chapter 1: What’s New in Flash MX 2004 ActionScript

• The TextField.condenseWhite property lets you remove extra white space from HTML text

fields that are rendered in a browser.

• The TextField.mouseWheelEnabled property lets you specify whether a text field’s contents

should scroll when the mouse pointer is positioned over a text field and the user rolls the mouse wheel.

• The “TextField.StyleSheet class” lets you create a style sheet object that contains text

formatting rules such as font size, color, and other formatting styles.

• The TextField.styleSheet property lets you attach a style sheet object to a text field.

• The TextFormat.getTextExtent() method accepts a new parameter, and the object it

returns contains a new member.

• The XML.addRequestHeader() method lets you add or change HTTP request headers (such

Content-Type or SOAPAction) sent with POST actions.

New security model and legacy SWF files

Rules for how Flash Player determines whether two domains are the same have changed in Flash Player 7. In addition, rules that determine whether and how a SWF file served from an HTTP domain can access a SWF file or load data from an HTTPS domain have changed. In most cases, these changes won’t affect you unless you are porting your existing SWF files to Flash Player 7.

However, if you have SWF files published for Flash Player 6 or earlier that load data from a file stored on a server, and the calling SWF file is playing in Flash Player 7, the user might see a dialog box that didn’t appear before, asking whether to allow access. You can prevent this dialog box from appearing by implementing a policy file on the site where the data is stored. For more information on this dialog box, see “About compatibility with previous Flash Player security

models” on page 294.

You might also need to implement a policy file if you are using runtime shared libraries. If either the loading or loaded SWF file is published for Flash Player 7 and the loading and loaded files aren’t served from the exact same domain, use a policy file to permit access. For more information on policy files, see “About allowing cross-domain data loading” on page 290.

Porting existing scripts to Flash Player 7

As with any new release, Flash Player 7 supports more ActionScript commands than previous versions of the player; you can use these commands to implement more robust scripts. (See “New

and changed language elements” on page 12.)However, if you used any of these commands in

your existing scripts, the script might not work correctly if you publish it for Flash Player 7.

For example, if you have a script with a function named compile correctly but might not run as expected in Flash Player 7, because class (making it a reserved word) in ActionScript. You can fix your script by renaming the Error function to something else, such as

“Keywords and reserved words” on page 32.

ErrorCondition. For a complete list of reserved words, see

Error, the script might appear to

Error is now a built-in

Porting existing scripts to Flash Player 7 13

Also, Flash Player 7 implements several changes that affect how one SWF file can access another SWF file, how external data can be loaded, and how local settings and data (such as privacy settings and locally persistent shared objects) can be accessed. Finally, the behavior of some existing features has changed.

If you have existing scripts written for Flash Player 6 or earlier that you want to publish for Flash Player 7, you might need to modify the scripts so they conform with the implementation of Flash Player 7 and work as designed. These modifications are discussed in this section under the following headings:

• “ECMA-262 compliance” on page 14

• “Domain-name rules for settings and local data” on page 15

• “Cross-domain and subdomain access between SWF files” on page 15

• “HTTP to HTTPS protocol access between SWF files” on page 18

• “Server-side policy files for permitting access to data” on page 19

ECMA-262 compliance

Several changes were implemented in Flash Player 7 to conform more closely to the ECMA-262 Edition 3 standard (see www.ecma-international.org/publications/standards/Ecma-262.htm). In addition to the class-based programming techniques available in ActionScript 2.0 (see “New

object-oriented programming model” on page 21), other features have been added and certain

behaviors have changed. Also, when publishing for Flash Player 7 and using ActionScript 2.0, you can cast one object type to another. For more information, see “Casting objects” on page 42. These capabilities don’t require you to update existing scripts; however, you might want to use them if you publish your scripts to Flash Player 7 and then continue to revise and enhance them.

Unlike the changes mentioned above, the changes listed in the following table (some of which also improve ECMA compliance) can cause existing scripts to work differently than they did before. If you used these features in existing scripts that you want to publish to Flash Player 7, review the changes to make sure your code still works as intended or to determine whether you need to rewrite your code. In particular, because cases, you should initialize all variables in scripts that you port to Flash Player 7.

undefined is evaluated differently in certain

SWF file published for Flash Player 7 SWF file published for earlier versions of

Flash Player

Case-sensitivity is enforced (variable names that differ only in capitalization are interpreted as being different variables). This change also affects files loaded with with

“Case sensitivity” on page 28.

Evaluating

NaN. myCount +=1;

trace(myCount); // NaN

14 Chapter 1: What’s New in Flash MX 2004 ActionScript

#include and external variables loaded

LoadVars.load(). For more information, see

undefined in a numeric context returns

Case-sensitivity is not supported (variable names that differ only in capitalization are interpreted as being the same variable).

Evaluating undefined in a numeric context returns 0.

myCount +=1; trace(myCount); // 1

SWF file published for Flash Player 7 SWF file published for earlier versions of

Flash Player

When undefined is converted to a string, the result is

undefined. firstname = "Joan ";

lastname = "Flender"; trace(firstname + middlename + lastname); // Joan undefinedFlender

When you convert a string to a Boolean value, the result is

true if the string has a length greater than

zero; the result is

When setting the length of an array, only a valid number string sets the length. For example, "6" works but " 6" or "6xyz" does not.

my_array=new Array(); my_array[" 6"] ="x"; trace(my_array.length); // 0 my_array["6xyz"] ="x"; trace(my_array.length); // 0 my_array["6"] ="x"; trace(my_array.length); // 7

false for an empty string.

When undefined is converted to a string, the result is an empty string ("").

firstname = "Joan "; lastname = "Flender"; trace(firstname + middlename + lastname); // Joan Flender

When you convert a string to a Boolean value, the string is first converted to a number; the result is otherwise.

When setting the length of an array, even a malformed number string sets the length.

my_array=new Array(); my_array[" 6"] ="x"; trace(my_array.length); // 7 my_array["6xyz"] ="x"; trace(my_array.length); // 7 my_array["6"] ="x"; trace(my_array.length); // 7

true if the number is nonzero, false

Domain-name rules for settings and local data

In Flash Player 6, superdomain matching rules are used by default when accessing local settings (such as camera or microphone access permissions) or locally persistent data (shared objects). That is, the settings and data for SWF files hosted at here.xyz.com, there.xyz.com, and xyz.com are shared and are all stored at xyz.com.

In Flash Player 7, exact-domain matching rules are used by default. That is, the settings and data for a file hosted at here.xyz.com are stored at here.xyz.com, the settings and data for a file hosted at there.xyz.com are stored at there.xyz.com, and so on.

A new property,

System.exactSettings, lets you specify which rules to use. This property is

supported for files published for Flash Player 6 or later. For files published for Flash Player 6, the default value is Flash Player 7, the default value is

false, which means superdomain matching rules are used. For files published for

true, which means exact-domain matching rules are used.

If you use settings or persistent local data and want to publish a Flash Player 6 SWF file for Flash Player 7, you might need to set this value to

For more information, see

System.exactSettings in Flash ActionScript Language Reference

false in the ported file.

Help.

Cross-domain and subdomain access between SWF files

When you develop a series of SWF files that communicate with each other—for example, when using

loadMovie(), MovieClip.loadMovie(), MovieClipLoader.LoadClip(), or Local

Connection objects—you might host the SWF files in different domains or in different subdomains of a single superdomain.

Porting existing scripts to Flash Player 7 15

In files published for Flash Player 5 or earlier, there were no restrictions on cross-domain or subdomain access.

In files published for Flash Player 6, you could use the or

System.security.allowDomain() method to specify permitted cross-domain access (for

LocalConnection.allowDomain handler

example, to let a file at someSite.com be accessed by a file at someOtherSite.com), and no command was needed to permit subdomain access (for example, a file at www.someSite.com could be accessed by a file at store.someSite.com).

Files published for Flash Player 7 implement access between SWF files differently from earlier versions in two ways. First, Flash Player 7 implements exact-domain matching rules instead of superdomain matching rules. Therefore, the file being accessed (even if it is published for a Player version earlier than Flash Player 7) must explicitly permit cross-domain or subdomain access; this topic is discussed in this section. Second, a file hosted at a site using a secure protocol (HTTPS) must explicitly permit access from a file hosted at a site using an insecure protocol (HTTP or FTP); this topic is discussed in the next section (see “HTTP to HTTPS protocol access between

SWF files” on page 18).

The following table summarizes domain-matching rules in different versions of Flash Player:

Files published for Cross-domain access between

SWF files

Flash Player 5 or earlier No restrictions No restrictions

Flash Player 6 Superdomain matching No restrictions

Flash Player 7 Exact domain matching

Explicit permission for HTTPShosted files to access HTTP- or FTP-hosted files

Subdomain access between SWF files

Exact domain matching Explicit permission for HTTPShosted files to access HTTP- or FTP-hosted files

Because Flash Player 7 implements exact-domain matching rules instead of superdomain matching rules, you might have to modify existing scripts if you want to access them from files that are published for Flash Player 7. (You can still publish the modified files for Flash Player 6.) If you used any

LocalConnection.allowDomain() or System.security.allowDomain()

statements in your files and specified superdomain sites to permit, you must change your parameters to specify exact domains instead. The following code shows an example of changes you might have to make:

// Flash Player 6 commands in a SWF file at www.anyOldSite.com // to allow access by SWF files that are hosted at www.someSite.com // or at store.someSite.com System.security.allowDomain("someSite.com"); my_lc.allowDomain = function(sendingDomain) {

return(sendingDomain=="someSite.com"); } // Corresponding commands to allow access by SWF files // that are published for Flash Player 7 System.security.allowDomain("www.someSite.com", "store.someSite.com"); my_lc.allowDomain = function(sendingDomain) {

return(sendingDomain=="www.someSite.com" ||

sendingDomain=="store.someSite.com");

}

16 Chapter 1: What’s New in Flash MX 2004 ActionScript

You might also have to add statements such as these to your files if you aren’t currently using them. For example, if your SWF file is hosted at www.someSite.com and you want to allow access by a SWF file published for Flash Player 7 at store.someSite.com, you must add statements such as the following example to the file at www.someSite.com (you can still publish the file at www.someSite.com for Flash Player 6):

System.security.allowDomain("store.someSite.com"); my_lc.allowDomain = function(sendingDomain) {

return(sendingDomain=="store.someSite.com"); }

In addition, consider that if a Flash Player 6 application running within Flash Player 7 tries to access data outside its exact domain, Flash Player 7 domain-matching rules are enforced and the user is prompted to allow or deny access.

To summarize, you might have to modify your files to add or change

allowDomain statements if

you publish files for Flash Player 7 that meet the following conditions:

• You implemented cross-SWF scripting (using loadMovie(), MovieClip.loadMovie(),

MovieClipLoader.LoadClip(), or Local Connection objects).

• The called SWF file (of any version) is not hosted at a site using a secure protocol (HTTPS), or

the calling and called SWF files are both hosted at HTTPS sites. (If only the called SWF file is

HTTPS, see “HTTP to HTTPS protocol access between SWF files” on page 18.)

• The SWF files are not in same domain (for example, one file is at www.domain.com and one is

at store.domain.com).

You must make the following changes:

• If the called SWF file is published for Flash Player 7, include System.security.allowDomain

LocalConnection.allowDomain in the called SWF file, using exact domain-

name matching.

• If the called SWF file is published for Flash Player 6, modify the called file to add or change a

System.security.allowDomain or LocalConnection.allowDomain statement, using exact

domain-name matching, as shown in the code examples earlier in this section. You can publish

the modified file for either Flash Player 6 or 7.

• If the called SWF file is published for Flash Player 5 or earlier, port the called file to

Flash Player 6 or 7 and add a

domain-name matching, as shown in the code examples earlier in this section.

(LocalConnection objects aren’t supported in Flash Player 5 or earlier.)

For more information, see the tech note at www.macromedia.com/support/flash/ts/documents/

security_sandbox.htm.

System.security.allowDomain statement, using exact

Porting existing scripts to Flash Player 7 17

HTTP to HTTPS protocol access between SWF files

As discussed in the previous section, rules for cross-domain and subdomain access have changed in Flash Player 7. In addition to the exact-domain matching rules now being implemented, you must explicitly permit files hosted at sites using a secure protocol (HTTPS) to be accessed by files hosted at sites using an insecure protocol. Depending on whether the called file is published for Flash Player 7 or 6, you must implement either one of the

allowDomain statements (see “Cross-

domain and subdomain access between SWF files” on page 15), or use the new

LocalConnection.allowInsecure Domain or System.security.allowInsecureDomain()

statements.

Warning: Implementing an allowInsecureDomain() statement compromises the security offered by the HTTPS protocol. You should make these changes only if you can’t reorganize your site so that all SWF files are served from the HTTPS protocol.

The following code shows an example of the changes you might have to make:

// Commands in a Flash Player 6 SWF file at https://www.someSite.com // to allow access by Flash Player 7 SWF files that are hosted // at http://www.someSite.com or at http://www.someOtherSite.com System.security.allowDomain("someOtherSite.com"); my_lc.allowDomain = function(sendingDomain) {

return(sendingDomain=="someOtherSite.com"); } // Corresponding commands in a Flash Player 7 SWF file // to allow access by Flash Player 7 SWF files that are hosted // at http://www.someSite.com or at http://www.someOtherSite.com System.security.allowInsecureDomain("www.someSite.com",

"www.someOtherSite.com"); my_lc.allowInsecureDomain = function(sendingDomain) {

return(sendingDomain=="www.someSite.com" ||

sendingDomain=="www.someOtherSite.com");

}

You might also have to add statements such as these to your files if you aren’t currently using them. A modification might be necessary even if both files are in same domain (for example, a file in http://www.domain.com is calling a file in https://www.domain.com).

To summarize, you might have to modify your files to add or change statements if you publish files for Flash Player 7 that meet the following conditions:

• You implemented cross-SWF scripting (using loadMovie(), MovieClip.loadMovie(),

MovieClipLoader.LoadClip(), or Local Connection objects).

• The calling file is not hosted using an HTTPS protocol, and the called file is HTTPS.

You must make the following changes:

• If the called file is published for Flash Player 7, include

System.security.allowInsecureDomain or LocalConnection.allowInsecureDomain in

the called file, using exact domain-name matching, as shown in the code examples earlier in

this section. This statement is required even if the calling and called SWF files are in

same domain.

18 Chapter 1: What’s New in Flash MX 2004 ActionScript

• If the called file is published for Flash Player 6 or earlier, and both the calling and called files

are in same domain (for example, a file in http://www.domain.com is calling a file in https://

www.domain.com), no modification is needed.

• If the called file is published for Flash Player 6, the files are not in same domain, and you don’t

want to port the called file to Flash Player 7, modify the called file to add or change a

System.security.allowDomain or LocalConnection.allowDomain statement, using exact

domain-name matching, as shown in the code examples earlier in this section.

• If the called file is published for Flash Player 6 and you want to port the called file to Flash

Player 7, include

LocalConnection.allowInsecureDomain in the called file, using exact domain-name

matching, as shown in the code examples earlier in this section. This statement is required even

if both files are in same domain.

System.security.allowInsecureDomain or

• If the called file is published for Flash Player 5 or earlier, and both files are not in the same

domain, you can do one of two things. You can either port the called file to Flash Player 6 and

add or change a

matching, as shown in the code examples earlier in this section, or you can port the called file

to Flash Player 7, and include a

called file, using exact domain-name matching, as shown in the code examples earlier in

this section.

Server-side policy files for permitting access to data

A Flash document can load data from an external source by using one of the following data loading calls:

LoadVars.sendAndLoad(), loadVariables(), loadVariablesNum(), MovieClip.loadVariables()

(

NetServices.createGatewayConnection). Also, a SWF file can import runtime shared

libraries (RSLs), or assets defined in another SWF file, at runtime. By default, the data or RSL must reside in the same domain as the SWF file that is loading that external data or media.

System.security.allowDomain statement, using exact domain-name

System.security.allowInsecureDomain statement in the

XML.load(), XML.sendAndLoad(), LoadVars.load(),

, XMLSocket.connect(), and Macromedia Flash Remoting

To make data and assets in runtime shared libraries available to SWF files in different domains, you should use a cross-domain policy file. A cross-domain policy file is an XML file that provides a way for the server to indicate that its data and documents are available to SWF files served from certain domains, or from all domains. Any SWF file that is served from a domain specified by the server’s policy file is permitted to access data or RSLs from that server.

If you are loading external data, you should create policy files even if you don’t plan to port any files to Flash Player 7. If you are using RSLs, you should create policy files if either the calling or called file is published for Flash Player 7.

For more information, see “About allowing cross-domain data loading” on page 290.

Porting existing scripts to Flash Player 7 19

ActionScript editor changes

The ActionScript editor has been updated in several ways to make it more robust and easier to use. These changes are summarized in this section.

Word wrapping You can now use the Options pop-up menu in the Script pane, Debugger

panel, and Output panel to enable or disable word wrapping. You can also toggle word wrapping using the pop-up menu on the Actions panel. The keyboard shortcut is Control+Shift+W (Windows) or Command+Shift+W (Macintosh).

Viewing context-sensitive help When your pointer is positioned over an ActionScript

language element in the Actions toolbox or in the Script pane, you can use the View Help item in the context menu to display a help page about that element.

Importing scripts When you select Import Script from the pop-up menu in the Actions panel,

the imported script is copied into the script at the insertion point in your code file. In previous versions of Flash, importing a script overwrote the contents of the existing script.

Single-click breakpoints To add a debugging breakpoint before a line of code in the Debugger

panel or the Script pane on the Actions panel, you can click in the left margin. In previous versions of Flash, clicking in the left margin selected a line of code. The new way to select a line of code is to Control-click (Windows) or Command-click (Macintosh).

Normal and expert modes no longer in Actions panel In previous versions of Flash, you could

work in the Actions panel either in normal mode, in which you filled in options and parameters to create code, or in expert mode, in which you added commands directly into the Script pane. In Flash MX 2004 and Flash MX Professional 2004, you can work in the Actions panel only by adding commands directly to the Script pane. You can still drag commands from the Actions toolbox into the Script pane or use the Add (+) button above the Script pane to add commands to a script.

Pinning multiple scripts You can pin multiple scripts within a FLA file along the bottom of the

Script pane in the Actions panel. In previous versions of Flash, you could pin only one script at a time.

Script navigator The left side of the Actions panel now contains two panes: the Actions toolbox

and a new Script navigator. The Script navigator is a visual representation of the structure of your FLA file; you can navigate through your FLA file here to locate ActionScript code.

Integrated Script window for editing external files (Flash Professional only) You can use the

ActionScript editor in a Script window (separate from the Actions panel) to write and edit external script files. Syntax coloring, code hinting, and other preferences are supported in the Script window, and the Actions toolbox is also available. To display the Script window, use File > New, and select the type of external file you want to edit. You can have multiple external files open at the same time; filenames appear on tabs across the top of the Script window. (The tabs appear only in Windows.)

20 Chapter 1: What’s New in Flash MX 2004 ActionScript

Debugging changes

This section describes changes that improve your ability to debug your scripts.

Output window changed to Output panel You can now move and dock the Output panel in

the same way as any other panel in Flash.

Improved error reporting at compile time In addition to providing more robust exception

handling, ActionScript 2.0 provides several new compile-time errors. For more information, see

Appendix A, “Error Messages,” on page 305.

Improved exception handling The Error class and the throw and try..catch..finally

commands let you implement more robust exception handling.

New object-oriented programming model

The ActionScript language has grown and developed since its introduction several years ago. With each new release of Flash, additional keywords, objects, methods, and other language elements have been added to the language. However, unlike earlier releases of Flash, Flash MX 2004 and Flash MX Professional 2004 introduce several new language elements that implement objectoriented programming in a more standard way than before. Because these language elements represent a significant enhancement to the core ActionScript language, they represent a new version of ActionScript: ActionScript 2.0.

ActionScript 2.0 is not a new language. Rather, it comprises a core set of language elements that make it easier to develop object-oriented programs. With the introduction of keywords such as

class, interface, extends, and implements, ActionScript syntax is now easier to learn for

programmers who are familiar with other languages. New programmers can learn more standard terminology that they can apply to other object-oriented languages they might study in the future.

The object-oriented programming (OOP) features in ActionScript 2.0 are based on the ECMAScript 4 Draft Proposal currently in development by ECMA TC39-TG1 (see

www.mozilla.org/js/language/es4/index.html). Because the ECMA-4 proposal is not yet a

standard, and because it is still changing, ActionScript 2.0 does not conform exactly to this specification.

ActionScript 2.0 supports all the standard elements of the ActionScript language; it lets you write scripts that more closely adhere to standards used in other object-oriented languages, such as Java. ActionScript 2.0 should be of interest primarily to intermediate or advanced Flash developers who are building applications that require the implementation of classes and subclasses. ActionScript 2.0 also lets you declare the object type of a variable when you create it (see “Strict

data typing” on page 41) and provides significantly improved compiler errors (see Appendix A, “Error Messages,” on page 305).

The following list shows the language elements that are new in ActionScript 2.0:

• class

• extends

• implements

New object-oriented programming model 21

• interface

• dynamic

• static

• public

• private

• get

• set

• import

Key facts about ActionScript 2.0 include the following points:

• Scripts that use ActionScript 2.0 to define classes or interfaces must be stored as external script

files, with a single class defined in each script; that is, classes and interfaces cannot be defined

in the Actions panel.

• You can import individual class files implicitly (by storing them in a location specified by

global or document-specific search paths and then using them in a script) or explicitly (by

using the

by using wildcards.

import command); you can import packages (collections of class files in a directory)

• Applications developed with ActionScript 2.0 are supported by Flash Player 6 and later.

Caution: The default publish setting for new files created in Flash MX 2004 is ActionScript 2.0. If you plan to modify an existing FLA file to use ActionScript 2.0 syntax, ensure that the FLA file specifies ActionScript 2.0 in its publish settings. If it does not, your file will compile incorrectly, although Flash will not generate compiler errors.

For more information on using ActionScript 2.0 to write object-oriented programs in Flash, see

Chapter 10, “Creating Custom Classes with ActionScript 2.0,” on page 247.

Although using ActionScript 2.0 is recommended, you can continue to use ActionScript 1 syntax, especially if you are doing more traditional Flash work such as simple animation that doesn’t require user interaction.

22 Chapter 1: What’s New in Flash MX 2004 ActionScript

CHAPTER 2

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 Flash ActionScript Language Reference. Applying the basics of ActionScript in a way that creates elegant programs can be a challenge for users who are new to ActionScript. For more information on how to apply the rules described in this section, see “Using Best Practices” on page 65.

This section contains the following topics:

• “Differences between ActionScript and JavaScript” on page 24

• “Terminology” on page 24

• “Syntax” on page 28

• “About data types” on page 34

• “Assigning data types to elements” on page 39

• “About variables” on page 44

• “Using operators to manipulate values in expressions” on page 49

• “Specifying an object’s path” on page 57

• “Using condition statements” on page 58

• “Using built-in functions” on page 60

• “Creating functions” on page 61

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.

• ActionScript 2.0, the latest version of the ActionScript language, 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.

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 Actions panel).

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.

24 Chapter 2: ActionScript Basics

class keyword in an external script file (not in a script you are writing in the

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 34.

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

generated when a movie clip loads, the playhead enters a frame, 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. (There are also two event handlers,

on() and onClipEvent(), that you can assign directly to buttons and movie

clips.) In the Actions toolbox, each ActionScript object that has event handler methods or event listeners has a subcategory called Events or 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 “Handling Events” on page 167.

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

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

+ is an operator.

x + 2, x and 2 are

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

more information, see “Creating functions” on page 61.

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

character must be a letter, underscore ( letter, number, underscore, or dollar sign. For example,

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

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

firstName is the name of a variable.

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.

Terminology 25

Instance names are unique names that let you target instances you create, or movie clip and

button instances on the Stage. 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();

You use the Property inspector to assign instance names to instances on the Stage. For example, a master symbol in the library could be called the SWF file could have the instance names following code sets a variable called

score inside each movie clip instance by using

counter and the two instances of that symbol in

scorePlayer1_mc and scorePlayer2_mc. The

instance names:

this.scorePlayer1_mc.score = 0; this.scorePlayer2_mc.score = 0;

You can use strict data typing when creating instances so that code hints (see “Using code hints”

on page 147) appear as you type your code. For more information, see “Strictly typing objects to trigger code hints” on page 145.

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 32.

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.

26 Chapter 2: ActionScript Basics

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.

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

For example, the following

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

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

directory (see “Understanding the classpath” on page 268).

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

if statement

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 name a movie clip instance in the movie clip Property inspector. (The main Timeline always has the name

_root.) 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

stereoControl.volume

volume property of the object named stereoControl:

For more information on target paths, see “Using absolute and relative target paths” in Using Flash.

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 44.

Terminology 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 28

• “Dot syntax” on page 29

• “Slash syntax” on page 30

• “Curly braces” on page 30

• “Semicolons” on page 31

• “Parentheses” on page 31

• “Comments” on page 31

• “Keywords and reserved words” on page 32

• “Constants” on page 34

Case sensitivity

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

When you publish files for Flash Player 7 or later, Flash implements case sensitivity whether you are using ActionScript 1 or ActionScript 2.0. This means that keywords, class names, variables, method names, and so on are all case sensitive. For example:

// In file targeting Flash Player 7 // and either ActionScript 1 or ActionScript 2.0 // // Sets properties of two different objects cat.hilite = true; CAT.hilite = true;

book and Book)

// Creates three different variables var myVar:Number=10; var myvar:Number=10; var mYvAr:Number=10; // Does not generate an error var array:Array = new Array(); var date:Date = new Date();

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

Case-sensitivity is implemented for external scripts, such as ActionScript 2.0 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.

28 Chapter 2: ActionScript Basics

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.

When syntax coloring is enabled, language elements written with correct capitalization are blue by default. For more information, see “Keywords and reserved words” on page 32 and “Syntax

highlighting” on page 144.

Dot syntax

In ActionScript, a dot (

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

clip. It is also used to identify the target path to a movie clip, variable, function, or object. A dot syntax expression begins with the name of the object or movie clip followed by a dot and ends with the element you want to specify.

For example, the expression

As another example, movie clip variable of the instance

_x movie clip property indicates a movie clip’s x axis position on the Stage. The

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

submit is a variable set in the form movie clip, which is nested inside the

shoppingCart. The expression shoppingCart.form.submit = true sets the submit

form to true.

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

bounce() method of the ball object would be called as follows:

ball.bounce();

Dot syntax also uses three special aliases, _root, _parent, and _global. The alias _root refers to the main Timeline. You can use the the following statement calls the function

_root alias to create an absolute target path. For example,

buildGameBoard() in the movie clip functions on

the main Timeline:

_root.functions.buildGameBoard();

You can use the alias _parent to refer to a movie clip in which the current object is nested. You can also use nested inside the movie clip

animal_mc to stop:

this._parent.stop();

_parent to create a relative target path. For example, if the movie clip dog_mc is

animal_mc, the following statement on the instance dog_mc tells

You can use the alias _global to indicate, without having to use a target path, that an object is available to all Timelines in your document. For example, the following statement defines the function

_global.response = function() {

}

response that is available to all Timelines:

if (myVar <= 19) {

myResponse = "25% discount for 20 or more orders";

} else {

myResponse = "Thanks for your order";

}

For more information, see _parent, _global object, and _root. in Flash ActionScript Language Reference.

Syntax 29

Slash syntax

Slash syntax was used in Flash 3 and 4 to indicate the target path of a movie clip or variable. This syntax is still supported by Flash Player 7, but its use is not recommended, and slash syntax is not supported in ActionScript 2.0. However, if you are creating content intended specifically for Flash Player 4, you must use slash syntax. For more information, see “Using slash syntax”

on page 321.

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. For recommended guidelines on formatting code, see Chapter 3, “Formatting code,” on page 76.

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() {