JavaScript: The Definitive Guide, 6th Edition

Object-Oriented Techniques in JavaScript

So far in this chapter we’ve covered the architectural fundamentals of classes in JavaScript: the importance of the prototype object, its connections to the constructor function, how the instanceof operator works, and so on. In this section we switch gears and demonstrate a number of practical (though not fundamental) techniques for programming with JavaScript classes. We begin with two nontrivial example classes that are interesting in their own right but also serve as starting points for the discussions that follow.

Example: A Set Class

A set is a data structure that represents an unordered collection of values, with no duplicates. The fundamental operations on sets are adding values and testing whether a value is a member of the set, and sets are generally implemented so that these operations are fast. JavaScript’s objects are basically sets of property names, with values associated with each name. It is trivial, therefore, to use an object as a set of strings. Example 9-6 implements a more general Set class in JavaScript. It works by mapping any JavaScript value to a unique string, and then using that string as a property name. Objects and functions do not have a concise and reliably unique string representation, so the Set class must define an identifying property on any object or function stored in the set.

Example 9-6. Set.js: An arbitrary set of values

function Set() {          // This is the constructor
    this.values = {};     // The properties of ...