JavaScript

18Upcoming Class Features

WHAT'S IN THIS CHAPTER?

• Public class fields
• Private class fields, instance methods, and accessors
• Static class fields and private static methods

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 about upcoming class features that are almost certain to be in ES2021, and which are stable enough (or nearly stable enough) to use with transpilation today (or even without, in some cases, in modern environments): class fields; private fields and methods/accessors; and static fields and private static methods/accessors.

PUBLIC AND PRIVATE CLASS FIELDS, METHODS, AND ACCESSORS

ES2015's class syntax was intentionally just a starting point. Multiple proposals that are likely to be adopted in ES2021 extend it with additional useful features:

• Public field (property) definitions
• Private fields
• Private instance methods and accessors
• Public static fields
• Private static fields
• Private static methods

These make the already-useful¹ class syntax markedly more useful, taking tasks that used to require hiding things in closures, assignments after-the-fact, behind-the-scenes use of WeakMaps, awkward syntax, etc., and making them simple syntax, and potentially improving the ways JavaScript engines can optimize the results as well.

The enhancements are spread across multiple proposals, which may advance at different rates, ...