Chapter 9. Classes, Constructors, and Prototypes

JavaScript objects were introduced in Chapter 7. That chapter treated each object as a unique set of properties, different from every other object. In many object-oriented programming languages, it is possible to define a class of objects and then create individual objects that are instances of that class. You might define a class named Complex to represent and perform arithmetic on complex numbers, for example. A Complex object would represent a single complex number and would be an instance of that class.

JavaScript does not support true classes the way that languages like Java, C++, and C# do.^[*] Still, however, it is possible to define pseudoclasses in JavaScript. The tools for doing this are constructor functions and prototype objects. This chapter explains constructors and prototypes and includes examples of several JavaScript pseudo-classes and even pseudosubclasses.

^[*] True classes are planned for JavaScript 2.0, however.