Dojo: The Definitive Guide

Multiply Inheriting with Mixins

The previous section introduced how Dojo simulates class-based inheritance and pointed out some critical issues involving JavaScript's finer points that are central to developing with Dojo. Although the primary example demonstrated single inheritance in which a Shape superclass provided the basis for a Circle subclass, Dojo also provides a limited form of multiple inheritance.

The process of defining inheritance relationships by weaving together Function objects in this way is referred to as prototype chaining because it's through JavaScript's Object.prototype property that the hierarchy is defined. (Recall that Example 10-2 illustrated this concept within the boilerplate of manually defining an inheritance relationship between a shape and a circle.)

Dojo simulates class-based inheritance by building upon the concept of prototype chaining to establish the hierarchy for single inheritance contexts. However, employing multiple-inheritance relationships is a little bit different because JavaScript limits Function objects to having only one built-in prototype property.

As you might imagine, there are a number of approaches that could be used to circumvent this issue. The approach that Dojo uses is to leverage prototype chaining so that you define a single prototypical ancestor that is the basis for prototype chaining—but at the same time, allowing you to provide other mixins that get injected into the prototypal ancestor. In other words, a class can have ...