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 2: Variables

When you define a variable on a timeline, that variable is accessible

from all the other frames of that timeline.

Scenario 2: Accessing a value defined later on the same timeline

What happens if we try instead to access a variable before the frame in which it is

assigned a value?

Suppose we add the following code to frame 30 of a movie’s main timeline:

password = "let_me_in";

gotoAndStop(15);

and on frame 15 we add:

trace(password);

When the movie plays, we see the following in the Output window:

undefined

let_me_in

Here’s why: when the movie’s playhead reaches frame 15, Flash displays the value of

password in the Output window. The first time through, password does not exist, so

Flash displays

undefined. However, when the playhead reaches frame 30, password is

created and assigned the value “let_me_in”. Then the playhead is sent back to frame

15 (gotoAndStop(15)), causing frame 15’s code to execute again. This time, even

though

password is defined on a later frame than our trace(password) statement, it is

still part of the same timeline; so, its value exists, and Flash displays it in the Output

window.

Any variable declared on a timeline is available to all the scripts of its

timeline for as long as that timeline exists. However, a variable’s value

is not defined until ...