ActionScript for Flash MX: The Definitive Guide, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 9: Functions

How do you know where to define your functions? If the function is

going to be used just for a single movie clip, define it on the movie clip

of interest. If the function is going to be used by multiple movie clips,

define it on the main timeline as a global function. We’ll discuss code

organization when we study object-oriented programming in

Chapter 12.

Function Life Span

A function defined on a movie clip timeline is lost when that clip is removed from

the Stage. An attempt to invoke a function that was defined in a clip that no longer

exists will fail silently. In Flash 5, defining a function on the main movie timeline is

the best way to ensure the function’s permanence, because the main timeline per-

sists throughout the movie. As of Flash 6, the most permanent location for a func-

tion is on the

_global object, as described in the previous section.

Note that functions in a frame’s script are initialized and become available when the

playhead first enters the frame containing the script. Therefore, we can use a func-

tion invocation before the declaration of the function, as long as both are in the same

keyframe’s script. For example:

// Invoke the tellTime() function before its declaration statement

tellTime();

// Declare the tellTime() function

function tellTime ...