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

// Store a function literal in a variable

var mouseCoords = function () { return [ _xmouse, _ymouse ]; };

// Now we can execute the function

mouseCoords();

Note that because ActionScript does not support JavaScript’s Function( ) construc-

tor, dynamic functions cannot be composed at runtime, as they can in JavaScript.

As we’ll see in Chapter 12, function literals are often used when assigning methods

to classes or objects. For example:

Ball.prototype.startMoving = function ( ) {

// Movement code goes here

};

is the same as:

Ball.prototype.startMoving = startMoving;

function startMoving ( ) {

// Movement code goes here

}

However, there are three subtle differences between function literals and standard

function declarations:

• When assigned as a method, a function literal does not leave an extraneous func-

tion reference defined in the scope of the function declaration. For example, in

the first Ball example (assuming the Ball code is attached to the main timeline), a

function literal is stored in

Ball.prototype.startMoving and no separate func-

tion reference remains defined on

_root. But in the second example, a reference

to startMoving( ) exists both in

Ball.prototype.startMoving and on _root.

• A standard function declaration does not end in a semicolon, whereas a