ActionScript 3.0 overview(1)

ActionScript 3.0 overview

ActionScript 3.0 is a powerful, object-oriented programming language that signifies an important step in the evolution of the capabilities of the Flash Player runtime. The motivation driving ActionScript 3.0 is to create a language ideally suited for rapidly building rich Internet applications, which have become an essential part of the web experience.

Earlier versions of ActionScript offered the power and flexibility required for creating truly engaging online experiences. ActionScript 3.0 now further advances the language, providing superb performance and ease of development to facilitate highly complex applications, large datasets, and object-oriented, reusable code bases. With ActionScript 3.0, developers can achieve excellent productivity and performance with content and applications that target Flash Player.

ActionScript 3.0 is based on ECMAScript, the international standardized programming language for scripting. ActionScript 3.0 is compliant with the ECMAScript Language Specification, Third Edition (ECMA-262). It also contains functionality based on ongoing work on ECMAScript Edition 4, occurring within the ECMA standards body.

ActionScript is executed by the ActionScript Virtual Machine (AVM) built into the Flash Player. AVM1, the virtual machine used to execute legacy ActionScript code, powers Flash Player today and makes possible a wide range of interactive media and rich Internet applications.

However, developers have started to push AVM1 to its limits; their project requirements now demand a major breakthrough. ActionScript 3.0 introduces a new highly optimized ActionScript Virtual Machine, AVM2, which dramatically exceeds the performance possible with AVM1. As a result, ActionScript 3.0 code executes up to 10 times faster than legacy ActionScript code.

The new AVM2 virtual machine is available in Flash Player 9, and will be the primary virtual machine for ActionScript execution going forward. The older AVM1 will continue to be supported by Flash Player for backwards compatibility with existing and legacy content.

There are numerous products that generate content and applications targeted at the Flash Player runtime. Often these products incorporate support for ActionScript to add interactivity and behavior to their output. In the Adobe product family, professional designers and developers might use ActionScript within several tools and servers—such as Flash, Flex, and Flash Media Server—to create content and applications for Flash Player. The Flex product family, including the new Eclipse-based Flex Builder 2 IDE, will be the first product line to access the new capabilities of ActionScript 3.0.

Goals of ActionScript 3.0

We wanted ActionScript 3.0 to deliver an improved, consistent programming model; compliance with industry standards; and performance an order of magnitude greater than what we delivered in the past. Although ActionScript 3.0 represents a new programming model for the runtime, it is one that will be familiar to developers with a basic knowledge of object-oriented programming.

ActionScript 3.0 is designed to address the following goals:

• Safety: The language supports type safety so developers can write unambiguous, easily maintainable code.
• Simplicity: The language is intuitive enough for developers to be able to read and write programs without constantly consulting a reference manual.
• Performance: The language enables developers to write complex programs that perform efficiently and responsively.
• Compatibility: The language provides a short backward and forward compatibility path and a significant overlap with industry standards. ActionScript 3.0 is a dialect of ECMAScript which formalizes the features of ActionScript 2.0, adds the capabilities of ECMAScript for XML (E4X), and unifies the language into a coherent whole.

Features of ActionScript 3.0

ActionScript 3.0 consists of two parts: the core language and the Flash Player API. The core language defines the basic building blocks of the programming language, such as statements, expressions, conditions, loops, and types. The Flash Player API is made up of classes that represent and provide access to Flash Player–specific functionality

ActionScript 3.0 contains a host of powerful new features that can greatly speed the development process. Regular expression support enables a variety of powerful operations on text. ECMAScript for XML (E4X) transforms XML into a native data type, dramatically simplifying XML processing. The new Display List API makes working with visual objects far more straightforward and consistent. The standardized DOM event model cements the way those objects talk and respond to each other at runtime. These are only a few of the many new capabilities of ActionScript 3.0.