Professional JavaScript for Web Developers, 4th Edition

5Basic Reference Types

WHAT'S IN THIS CHAPTER?

• Working with objects
• Understanding basic JavaScript data types
• Working with primitives and primitive wrappers

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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.

NOTE   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 chapter.

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:

let now = new Date();

This code creates a new instance of the Date reference type and stores it in the variable now ...