1.1. What's New in ActionScript 3.0?

If you’re familiar with ActionScript or you’re learning it based on experience with another programming language, you may want to know what ActionScript 3.0 has to offer. Although the third major version of the Flash Platform’s primary scripting language contains much that will be familiar to users of prior versions, it’s probably best to think of ActionScript 3.0 as entirely new, for a few simple reasons.

First, a few things are quite different, such as how events are handled and the way assets are displayed. Second, subtle changes run throughout the language. (These are usually small concerns, such as a slight change in the name of a property, but if you are used to ActionScript 2.0, for example, old habits can die hard.) Most importantly, ActionScript 3.0 has been rewritten from the ground up and uses a different code base than prior versions of the language. This optimization provides relatively dramatic performance increases, but it means that ActionScript 3.0 code cannot be mixed with prior versions of the language in the same file.