ActionScript is an ECMAScript-based programming language used for scripting Adobe Flash movies and applications. Since both ActionScript and JavaScript are based on the same ECMAScript syntax, fluency in one theoretically translates easily to the other. However, while JavaScript's DOM is browser window-, document- and form-centric, the ActionScript DOM is movie-centric, which may include animations, audio, text and event handling.

ActionScript first appeared in its current syntax with the release of Flash 5, which was the first thoroughly programmable version of Flash. This ActionScript release was named ActionScript 1.0. Flash 6 (MX) then further broadened the utility of the programming environment by adding a number of built-in functions and allowing better programmatic control of movie elements. Flash 7 (MX 2004) introduced ActionScript 2.0, which added strong typing and class-based programming features such as explicit class declarations, inheritance, interfaces, and Strict Data Typing. ActionScript 1.0 and 2.0 share the same compiled form within Flash SWFs.

Timeline

Flash Lite 1.0 and 1.1: Flash Lite is the Flash technology specifically developed for mobile phones and consumer electronics devices. Flash Lite 1.1 supports Flash 4 ActionScript.
Flash Lite 2.1: Added support for Flash 7 ActionScript 2.0.
Flash Player 2: First version with scripting support, actions included gotoAndPlay, gotoAndStop, nextFrame and nextScene for timeline control.
Flash Player 3: Expanded basic scripting support with the ability to load external SWFs (loadMovie).
Flash Player 4: First player with a full scripting implementation (called Actions). The scripting was a slash based syntax and contained support for loops, conditionals, variables and other basic language constructs.
Flash Player 5: Included the first version of true ActionScript. Used Prototype-based programming based on ECMAScript, and allowed full Procedural programming and Object-Oriented programming.
Flash Player 6: Added an event handling model, and support for switch.
Flash Player 7: Flash Player 7 offered some new features such as CSS text and performance improvements. Macromedia Flash compilers released alongside Flash Player 7 also support ActionScript 2.0, a Class programming language based on the ECMAScript 4 Netscape Proposal. However, ActionScript 2.0 can cross compile to ActionScript 1.0 byte-code, so it can be run by FlashPlayer 6.
Flash Player 8: Further extended ActionScript 2.0 by adding new class libraries with APIs for controlling bitmap data at run-time, and file-upload.
Flash Player 9 (initially called 8.5): Added ActionScript 3.0 with the advent of a new virtual machine, called AVM2 (ActionScript Virtual Machine 2), which coexists with the previous AVM1 needed to support legacy content. Performance increases were a major objective for this release of the player including a new JIT compilation. This is the first release of the player to be titled Adobe Flash Player.

from : en.wikipedia.org