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 a variable is referenced in a frame script, Flash checks the current movie clip

for the variable. If the variable is not found in the movie clip (or its prototype), Flash

checks for a global variable of that name. If no global variable is found, Flash returns

undefined. When both a movie clip variable and a global variable of the same name

are defined, Flash retrieves the movie clip variable, because it is first in the search

order for the scope chain. Hence, a movie clip variable always overrides a global vari-

able of the same name.

By contrast, the scope chain for code in a nonnested function includes three scopes

(again, read from the bottom up):

• Global object (

_global)

• Enclosing movie clip object

• Local variables

When a variable is referenced from within a function, Flash checks first for a local

variable—defined with the var statement—within the function, as shown in

Example 2-5. If no local variable is found, Flash checks for a movie clip variable in

the movie clip in which the function was defined. (We’ll consider this topic, includ-

ing the behavior for nested functions, more thoroughly in Chapter 9.) If the variable

is not found in that movie clip (or its prototype), Flash checks for a global variable of

the same name. If no global variable is ...