JavaScript

4Classes

WHAT'S IN THIS CHAPTER?

• What is a class?
• Introducing the new class syntax
• Comparing with the older syntax
• Creating subclasses
• Inheriting methods and properties (prototype and static)
• Accessing inherited methods and properties
• Subclassing built-ins
• Computed method names
• Leaving off Object.prototype
• What new.target is and why you'd use it
• More to come in Chapter 18

CODE DOWNLOADS FOR THIS CHAPTER

You can download the code for this chapter at https://thenewtoys.dev/bookcode or https://www.wiley.com/go/javascript-newtoys.

In this chapter you'll learn how class syntax works for creating JavaScript constructors and associated prototype objects. We'll compare and contrast the new syntax with the old, highlight that it's still the same prototypical inheritance JavaScript is famous for, and explore how powerful and simple the new syntax is. You'll see how to create subclasses, including subclasses of built-ins (even ones that can't be subclassed in ES5 and earlier like Array and Error), how super works, and what new.target is for and how to use it.

This chapter doesn't cover features that are coming in ES2020 or ES2021 like public class fields, private class fields, and private methods. See Chapter 18 for coverage of those.

WHAT IS A CLASS?

Before looking at the new syntax, let's address the elephant in the room: JavaScript doesn't really have classes, does it? It just emulates them with prototypes, right?

That's a popular perspective, because people confuse ...