Professional, JavaScript® for Web Developers, Second Edition

Chapter 5. Reference Types

A reference value (object) is an instance of a specific reference type. In ECMAScript, reference types are structures used to group data and functionality together and are often incorrectly called classes. Although technically an object-oriented language, ECMAScript lacks some basic constructs that have traditionally been associated with object-oriented programming, including classes and interfaces. Reference types are also sometimes called object definitions, because they describe the properties and methods that objects should have.

Even though reference types are similar to classes, the two concepts are not equivalent. To avoid any confusion, the term class is not used in the rest of this book.

Again, objects are considered to be instances of a particular reference type. New objects are created by using the new operator followed by a constructor. A constructor is simply a function whose purpose is to create a new object. Consider the following line of code:

var person = new Object();

This code creates a new instance of the Object reference type and stores it in the variable person. The constructor being used is Object(), which creates a simple object with only the default properties and methods. ECMAScript provides a number of native reference types, such as Object, to help developers with common computing tasks.

The Object Type

Up to this point, most of the reference-value examples have used the Object type, which is one of the most often-used types in ECMAScript. ...