Event-Based AsynchronousCode Execution (ActionScript: The Definitive Guide)

10.2. Event-Based AsynchronousCode Execution

Some code does not execute in a predictable sequence. Instead, it executes when the ActionScript interpreter notices that one of a predetermined set of events has occurred. Many events involve some action by the user, such as clicking the mouse or pressing a key. Just as the playhead entering a new frame executes synchronous code attached to the frame, events can cause event-based code to execute. Event-based code (code that executes in response to an event) is said to be executed asynchronously because the triggering of events can occur at arbitrary times.

Synchronous programming requires us to dictate, in advance, the timing of our code's execution. Asynchronous programming, on the other hand, gives us the ability to react dynamically to events as they occur. Asynchronous code execution is critical to ActionScript and to interactivity itself.

This chapter explores asynchronous (event-based) programming in Flash and catalogs the different events supported by ActionScript.