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xbObjects

ClassZ.prototype.sayMessageZ = function () {

alert(this.messageZ);

};

ClassZ._initialized = true;

}

Note that two lines inherit the properties (using the

apply()

method), and two lines inherit the meth-

ods (using the

inheritFrom()

) method. As discussed earlier, the order in which the inheritance hap-

pens is important, and it is generally better to always inherit methods in the same order as the properties

(meaning that if properties are inherited from

ClassX

and then

ClassY

, the methods should be inher-

ited in that same order).

The following code tests the multiple inheritance example:

var objZ = new ClassZ();

objZ.sayMessageX(); //outputs “This is X message. “

objZ.sayMessageY(); //outputs “This is Y message.”

objZ.sayMessageZ(); //outputs “This is Z message.”

The previous code calls three methods:

sayMessageX()

, which is inherited from

ClassX

, accesses the

messageX

property, also

inherited from

ClassX

sayMessageY()

, which is inherited from

ClassY

, accesses the

messageY

property, also

inherited from

ClassY

sayMessageZ()

, which is defined in

ClassZ

, accesses the

messageZ

property, also defined in

ClassZ

These three methods should output the appropriate message from the appropriate property, indicating

that the multiple inheritance has succeeded.

xbObjects

Netscape’s DevEdge site (

http://devedge.netscape.com

) contains a lot of useful information and

scripting tools for Web developers. One such tool is xbObjects (available for download from

http://

archive.bclary.com/xbProjects-docs/xbObject/

), written by Bob Clary of Netscape

Communications in 2001, when Netscape 6 (Mozilla 0.6) was first released. It supports all

versions of Mozilla since that time as well other modern browsers (IE, Opera, Safari).

Purpose

The purpose of xbObjects is to provide a stronger object-oriented paradigm to JavaScript, allowing not

only for inheritance but also for overloading of methods and the capability to call superclass methods.

To do this, xbObjects requires a number of steps be followed.

First, you must

the class, and in doing so, define which class to inherit from. This is done using

the following call:

_classes.registerClass(“Subclass_Name”, “Superclass_Name”);

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