.AS File Format

Introduction

ActionScript 1.0 is the scripting language of Macromedia Flash 5 (2000) and Flash MX (2002), and of Flash Player 5 and 6, which run it. Flash 5 was the first version to call its scripts ActionScript: it replaced the menu-built actions of Flash 4 with a language modelled on ECMA-262, the standard behind JavaScript, with dot syntax, functions and objects. The name ActionScript 1.0 was given to it afterwards, when Flash MX 2004 brought in ActionScript 2.0.

Nearly all ActionScript 1.0 lived inside Flash documents, typed into the Actions panel and attached to frames, buttons and movie clips. An .as file was a way to keep some of that code in a text file, to share it between documents or edit it in another editor: a frame script writes #include "file.as", and the compiler pastes the file’s text in at that point. The file itself has no structure beyond the language: it is a list of statements and function definitions.

The language is dynamically typed. Objects are made by constructor functions and share behaviour through prototypes; there are no classes. Code runs on timelines, in the scope of the movie clip that holds it. This variant covers the language as Flash 5 and Flash MX compile it; later versions of Flash could still publish ActionScript 1.0, and an .as file of loose code written for them is the same kind of file. An .as file dropped on any page opens in the explorer as text.

A typical file

An include file for Flash MX that builds a menu from a library symbol. The FLA’s first frame holds the line #include "menu.as", with no semicolon.

// menu.as: builds the site menu on the timeline that includes it.

var items = ["Home", "Work", "Contact"];

function buildMenu(target, x, y) {
    for (var i = 0; i < items.length; i++) {
        var item = target.attachMovie("menuItem", "item" + i, i);
        item._x = x;
        item._y = y + i * 24;
        item.label_txt.text = items[i];
        item.page = i + 2;
        item.onRelease = function () {
            _root.gotoAndStop(this.page);
        };
    }
}

buildMenu(this, 20, 40);

The language at a glance

Flash 5 and Flash MX

Flash MX only added to the language, so both are one format. What it added, all of it needing Flash Player 6 unless noted:

• the switch statement and the === and !== operators;
• instanceof, super, _global, setInterval and clearInterval;
• #initclip and #endinitclip, and Object.registerClass to give a movie clip symbol its own class;
• event handlers as function properties, such as onPress and onEnterFrame, and listener objects with addListener;
• movie clips made from nothing with createEmptyMovieClip, text fields with createTextField, and the drawing methods;
• new classes: Button, TextField, TextFormat, LoadVars, LocalConnection, SharedObject, Stage, System, Camera, Microphone, NetConnection, NetStream, Video and others;
• Function.call and Function.apply, Object.addProperty, watch and hasOwnProperty;
• Unicode text in the player, and UTF-8 include files.

Telling it apart

An .as file has no signature, so the language is told from the code. The explorer reads the text, skips comments and white space, and looks at what the code is made of: a package block means ActionScript 3.0, and a class or interface declaration at the top level means ActionScript 2.0. Anything else, loose statements and functions, is ActionScript 1.0.

Some signs point to Flash 5 or Flash MX in particular: a first line of //!-- UTF8; slash-syntax paths such as /menu:count; tellTarget, eq or add; and assignments to prototype and __proto__. Type annotations such as var n:Number mean the file was written for the ActionScript 2.0 compiler, even when it holds no class.

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)

Links