ActionScript for Flash MX: The Definitive Guide, Second Edition

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

Classes and Object-Oriented Programming

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The end of the inheritance chain

All objects descend from the top-level Object class. Hence, all objects inherit the prop-

erties defined in the Object constructor (for example, the toString( ) and valueOf( )

methods). We can, therefore, add new properties to every object in a movie by add-

ing new properties to the Object class. Properties attached to

Object.prototype will

proliferate throughout the entire class hierarchy, including all built-in objects, such as

Array, TextField, and even MovieClip objects. This approach can be used to make a

sort of global variable or function. In the following code, for example, we hardcode

the Stage width and height dimensions into the Object class

prototype. We can then

access that information from any movie clip (this technique was common in Flash 5

movies, although in Flash Player 6, the Stage dimensions are available as

Stage.width

and Stage.height):

Object.prototype.mainstageWidth = 550;

Object.prototype.mainstageHeight = 400;

trace(anyClip.mainstageWidth); // Displays: 550

Object.prototype properties are inherited not only by movie clips, but also by every

object, so even our own custom objects and instances of built-in classes such as

XML, Date, and Sound inherit properties assigned to

Object.prototype ...