ActionScript for Flash MX: The Definitive Guide, Second Edition

This is the Title of the Book, eMatter Edition

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Chapter 9

CHAPTER 9

Functions

I’m almost giddy to tell you about functions because they’re such a powerful part of

ActionScript. A function is simply a chunk of code that can be reused throughout a

program. Not only do functions lend enormous flexibility and convenience to our

scripts, they also give us control over Flash movie elements. I can hardly imagine

programming without functions—they ease performing common operations, from

sorting words to calculating the distance between two movie clips. We’ll introduce

functions in this chapter before learning how to create complex, powerful programs

using functions with objects in Chapter 12.

We’ll focus first on the simplest functions to understand—custom functions—the

functions we create in our scripts, as distinguished from the built-in functions pro-

vided with ActionScript.

The ECMA-262 specification refers to custom functions as program

functions and built-in functions as internal functions. We use the collo-

quial name in both cases rather than the formal specification’s termi-

nology.

By learning to create your own functions, you’ll become familiar with these funda-

mentals:

Function declaration or function definition

Creating functions for future use in our scripts.

Function invocation

Causing functions to execute. In other words,