ActionScript for Flash MX: The Definitive Guide, Second Edition

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

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Chapter 9: Functions

Built-in Functions

Although we’ve seen how to create user-defined functions, let’s not forget that

ActionScript comes with a bevy of built-in functions (akin to verbs in our language

analogy). We’ve already seen some built-in functions that allow us to manipulate

data. We’ve also touched on functions that control the Flash movie and the user

environment.

For example, to manipulate the playhead of a movie clip, we can call the

gotoAndPlay() function with a frame number as a parameter:

gotoAndPlay(5);

If you are a new programmer, you may be experiencing an epiphany. I hope you have

noticed that you invoke built-in functions using the function-call operator (the

parentheses) and an argument list (the value 5 in this case) just like our custom user-

defined functions! Built-in functions, such as gotoAndPlay(), are used just like the

functions we’ve been declaring ourselves. Custom functions typically do something

that a built-in ActionScript function doesn’t already offer. Like any custom function,

each built-in function has a name, zero or more optional or required arguments, and

a return value (although sometimes the value is

undefined).

Even though Flash has long referred to gotoAndPlay as an “Action,” we now see it in

its true form, as a built-in function. In Chapter ...