JavaScript: The Definitive Guide, Fourth Edition

Object-Oriented JavaScript

Although JavaScript supports a data type we call an object, it does not have a formal notion of a class. This makes it quite different from classic object-oriented languages such as C++ and Java. The common conception about object-oriented programming languages is that they are strongly typed and support class-based inheritance. By these criteria, it is easy to dismiss JavaScript as not being a true object-oriented language. On the other hand, we’ve seen that JavaScript makes heavy use of objects and that it has its own type of prototype-based inheritance. JavaScript is a true object-oriented language. It draws inspiration from a number of other (relatively obscure) object-oriented languages that use prototype-based inheritance instead of class-based inheritance.

Although JavaScript is not a class-based object-oriented language, it does a good job of simulating the features of class-based languages such as Java and C++. I’ve been using the term class informally throughout this chapter. This section more formally explores the parallels between JavaScript and true class-based inheritance languages such as Java and C++.^[30]

Let’s start by defining some basic terminology. An object, as we’ve already seen, is a data structure that contains various pieces of named data and may also contain various methods to operate on those pieces of data. An object groups related values and methods into a single convenient package, which generally makes programming easier ...