Dojo: The Definitive Guide

JavaScript Object Utilities

Three of Base's language utilities facilitate operations you may need to routinely perform on objects: mixin, extend, and clone.

Tip

Dojo uses mixin and extend in its dojo.declare implementation, which is the toolkit's mechanism for simulating class-based inheritance. dojo.declare is covered extensively in Chapter 10.

Mixins

JavaScript allows you to approximate lightweight classes by housing a collection of properties and methods inside a constructor function. You may then create object instances of these classes by invoking the constructor function with the new operator. As you might expect, it can sometimes be quite convenient to add additional properties to an object, whether it be to make something dynamic happen on-the-fly or as part of a well crafted design that maximizes code reuse. Either way, mixin provides a compact way of handling the implementation details for you.

Tip

In terms of object-oriented design with JavaScript, you'll see mixin used extensively throughout the toolkit to reuse blocks of code.

The API for using the toolkit's mixin functions entails providing an indeterminate number of objects, where the first objects gets the other objects mixed into it:

dojo.mixin(/*Object*/ o, /*Object*/ o, ...) //Returns Object

Here's an example of mixin:

function Man( ) { this.x = 10; } function Myth( ) { this.y = 20; } function Legend( ) { this.z = 30; } var theMan = new Man; var theMyth = new Myth; var theLegend = new Legend; function ManMythLegend( ) {} ...