Practical Modern JavaScript

Chapter 3. Classes, Symbols, Objects, and Decorators

Now that we’ve covered the basic improvements to the syntax, we’re in good shape to take aim at a few other additions to the language: classes and symbols. Classes provide syntax to represent prototypal inheritance under the traditional class-based programming paradigm. Symbols are a new primitive value type in JavaScript, like strings, Booleans, and numbers. They can be used for defining protocols, and in this chapter we’ll investigate what that means. When we’re done with classes and symbols, we’ll discuss a few new static methods added to the Object built-in in ES6.

3.1 Classes

JavaScript is a prototype-based language, and classes are mostly syntactic sugar on top of prototypal inheritance. The fundamental difference between prototypal inheritance and classes is that classes can extend other classes, making it possible for us to extend the Array built-in—something that was very convoluted before ES6.

The class keyword acts, then, as a device that makes JavaScript more inviting to programmers coming from other paradigms, who might not be all that familiar with prototype chains.

3.1.1 Class Fundamentals

When learning about new language features, it’s always a good idea to look at existing constructs first, and then see how the new feature improves those use cases. We’ll start by looking at a simple prototype-based JavaScript constructor and then compare that with the newer classes syntax in ES6.

The following ...