Dojo: The Definitive Guide

Simulating Classes with Dojo

Now that you've had a moment to ponder some of the various inheritance possibilities, it's time to introduce the toolkit's fundamental construct for declaring classes and simulating rich inheritance hierarchies. Dojo keeps it simple by tucking away all of the implementation details involved with class declarations and inheritance behind an elegant little function in Base called dojo.declare. This function is easy to remember because you're loosely declaring a class with it. Table 10-1 shows the brief API.

Table 10-1. dojo.declare API

Name	Comment
dojo.declare (/*String*/ className, /*Function|Function[]*/ superclass, /*Object*/ props)	Provides a compact way of declaring a constructor function. The className provides the name of the constructor function that is created, superclass is either a single Function object ancestor or an Array of Function object ancestors that are mixed in, and props provides an object whose properties are copied into the constructor function's prototype.

Tip

As you might suspect, declare builds upon the patterns provided by functions like extend, mixin, and delegate to provide an even richer abstraction than any one of those patterns could offer individually.

Example 10-5 illustrates how you could use dojo.declare to accomplish an inheritance hierarchy between a shape and circle. For now, consider this example as just an isolated bit of motivation. We'll discuss the finer points momentarily.

Example 10-5. Simulating class-based inheritance ...