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 12: Objects and Classes

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In ECMA-262, JavaScript, and ActionScript, the constructor property

is written to a class’s prototype (as

Class.prototype.constructor),

where instances of the class can retrieve it via the prototype chain.

However, ActionScript also adds a

constructor property directly to

instances (as

instanceName.constructor) effectively obscuring Class.

prototype.constructor. ActionScript’s nonstandard implementation is

considered a bug by Macromedia—the ECMA-262 standard requires

that an instance retrieve its constructor via

Class.prototype.

constructor

. In a future version of Flash, Macromedia will likely fix

this bug (that is, in the future

constructor will no longer be written

directly to instances). We’ll see how writing a

constructor property to

individual instances affects inheritance in the next section.

Advanced Issues with Standard SuperClass Assignment

As we’ve seen, the standard means for establishing a class’s superclass is:

SubClass.prototype = new SuperClass( );

When using the new operator to establish inheritance, some developers have encoun-

tered minor problems, discussed in detail next. To sidestep these problems, some

developers use the following unofficial technique, ...