.AS File Format

Introduction

ActionScript 2.0 is the language of Macromedia Flash MX 2004 (2003) and Flash 8 (2005), and of Adobe Flash CS3 and CS4, which still offered it beside ActionScript 3.0; Flash CS5 and CS6 could still compile it. Flex 1.0 and 1.5 used it too. It added classes, interfaces, packages and type annotations to the ActionScript of Flash MX, following the class syntax proposed for ECMAScript 4 at the time. The compiler checks the types, then turns the classes into the same prototype-based code that ActionScript 1.0 would have used, so the result runs in Flash Player 6 and later.

What changed for .as files is how they are found and what they hold. Each file holds exactly one class or interface, named after the file, and the compiler finds it on its own through the classpath when code uses the name: no #include is needed. Folders stand for packages, so the class com.example.ui.Counter is the file com/example/ui/Counter.as. Scripts in the FLA, frame code and button and clip handlers, are still written as before, now with type annotations if wanted, and loose-code .as files can still be included. An .as file dropped on any page opens in the explorer as text.

A typical file

A class for a movie clip symbol whose linkage settings name it as the symbol’s ActionScript 2.0 class. The file is com/example/ui/Counter.as, in a folder on the classpath.

import mx.utils.Delegate;

class com.example.ui.Counter extends MovieClip {
    private var count:Number = 0;
    private var label_txt:TextField;   // instances placed in the symbol
    private var plus_btn:Button;

    public function Counter() {
        plus_btn.onRelease = Delegate.create(this, increment);
        update();
    }

    public function get value():Number {
        return count;
    }

    private function increment():Void {
        count++;
        update();
    }

    private function update():Void {
        label_txt.text = String(count);
    }
}

The language at a glance

Flash MX 2004, Flash 8 and later

Each later version only added to ActionScript 2.0, so they are one format:

• Flash MX 2004 (Flash Player 7) brought the language itself, exceptions, the Error, MovieClipLoader, ContextMenu, PrintJob and TextField.StyleSheet classes, and the version 2 components with mx.events.EventDispatcher. Its 7.2 update added mx.utils.Delegate.
• Flash 8 (Flash Player 8) added the flash.display, flash.filters, flash.geom, flash.net, flash.external and flash.text packages, blend modes, bitmap caching and setTimeout.
• Flash CS3 and CS4 added nothing to the language. Flash Player 9 and 10 run ActionScript 2.0 in the same virtual machine as before, and add only a few properties, such as MovieClip.forceSmoothing.

Telling it apart

An .as file has no signature, so the language is told from the code. The explorer reads the text, skips comments, white space and import lines, and takes a file whose code is a class or interface declaration at the top level, perhaps after dynamic or intrinsic, as ActionScript 2.0. A file that starts with a package block is ActionScript 3.0 instead, and loose code is ActionScript 1.0.

The class name gives the package and so the folder the file belongs in: class com.example.ui.Counter should be Counter.as in com/example/ui. An ActionScript 3.0 file puts the same name in two places, package com.example.ui { public class Counter, and its members carry public, protected or internal where ActionScript 2.0 has only public and private.

Variants

• ActionScript 1.0 – loose code pulled in by #include, with prototype-based objects (Flash 5 and Flash MX)
• ActionScript 2.0 – one class or interface per file, found through the classpath, compiled for AVM1 (Flash MX 2004 to Flash CS4)
• ActionScript 3.0 – a package block with one public definition, compiled for the AVM2 (Flash CS3, Flex 2 and later)

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