Dojo: The Definitive Guide

One Problem, Many Solutions

In case you're locked into the inheritance paradigm, this section demonstrates multiple approaches to achieving similar results for a simple problem: modeling a circle object. In addition to being a good exercise in demonstrating some out-of-the-box thinking, this section also applies some of the language tools you learned about in Chapter 2.

Typical JavaScript Inheritance

JavaScript programmers have been simulating classes with Function objects for quite a while—sometimes at the expense of abusing the language, other times effectively to solve a particular problem. The inherent nature of a JavaScript Function object is the very mechanism that provides the footing for simulating classes. Namely, it acts as a constructor function that is used in conjunction with the new operator to create object instances, and it provides the template for those object instances that are created.

To illustrate, Example 10-1 provides a short code snippet that approximates a simple Shape class in JavaScript. Note that by convention, classes usually begin with a capital letter.

Tip

For just an added touch of simplicity, the examples in this chapter do not use namespaces for qualifying objects. In general, however, you will want to use namespaces, and we'll pick back up using namespaces in Chapter 12.

Example 10-1. A typical JavaScript class

// Define a class function Shape(centerX, centerY, color) { this.centerX = centerX; this.centerY = centerY; this.color = color; }; // Create ...