ActionScript: The Definitive Guide

Variable Scope

Earlier we learned how to create variables and retrieve their values using variables attached to a single frame of the main timeline of a Flash document. When a document contains multiple frames and multiple movie clip timelines, variable creation and value retrieval becomes a little more complicated.

To illustrate why, let’s consider several scenarios.

Scenario 1

Suppose we were to create a variable, x, in frame 1 of the main timeline. After creating x, we set its value to 10:

var x;
x = 10;

Then, in the next frame (frame 2), we attach the following code:

trace(x);

When we play our movie, does anything appear in the Output window? We created our variable in frame 1, but we’re attempting to retrieve its value in frame 2; does our variable still exist? Yes.

Tip

When you define a variable on a timeline, that variable is accessible from all the other frames of that timeline.

Scenario 2

Suppose we create and set x as we did in Scenario 1, but instead of placing the variable-setting code on frame 1 directly, we place it on a button in frame 1. Then, on frame 2, we attach the same code as before:

trace(x);

Does Scenario 2 also work? Yes. Because x is attached to our button, and our button is attached to the main timeline, our variable is indirectly attached to the main timeline. We may, therefore, access the variable from frame 2 as we did before.

Scenario 3

Suppose we create a variable named secretPassword on frame 1 of the main timeline. When the movie plays, the user must guess ...