ActionScript for Flash MX: The Definitive Guide, Second Edition

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

Variable Scope

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Determining the Type Manually

Automatic datatyping and conversion can be convenient, but, as Example 2-2 and

Example 2-3 illustrate, they may also produce unexpected results. Before performing

commands that operate on mixed datatypes, you may wish to determine a variable’s

datatype using the typeof operator:

productName = "Macromedia Flash"; // String value

trace(typeof productName); // Displays: "string"

Once we know a variable’s type, we can proceed conditionally. Here, for example,

we check whether a variable is a number before proceeding:

if (typeof age = = "number") {

// okay to carry on

} else {

trace ("Age isn't a number"); // Display an error message

}

For full details on the typeof operator, see Chapter 5.

Variable Scope

Earlier we learned how to create variables and retrieve their values. But all our vari-

ables were attached to a single frame of the main timeline of a Flash document.

When a document contains multiple frames and multiple movie clip timelines, vari-

able creation and value retrieval becomes a little more complicated.

Timeline Variables

To illustrate the use of timeline variables, let’s consider two simple scenarios.

Scenario 1: Accessing a value defined earlier on the same timeline

What happens when we define a variable in one frame of a timeline ...