Introducing Events

What exactly is an event? At its core, an event is an object that represents an occurrence and describes the conditions surrounding that occurrence, including but not limited to, a description of the event, called the event type, and the origin of the event, also known as the event target.

This is by no means a new concept. In the past, ActionScript users have had access to callback functions such as onClipEvent handlers and button actions. ActionScript 2.0 users might have used the elusive and poorly documented mx.events.EventDispatcher class—or perhaps the even more elusive and even less documented ASBroadcaster class. Java users are, no doubt, familiar with the Observer/Observable combo. And all of these use the principles defined in the Observer design pattern. What is new about the event system in ActionScript 3.0 is the way it's implemented across many different areas of the API with a consistent and robust design.