Programming TypeScript

Chapter 5. Classes and Interfaces

If you’re like most programmers coming from an object-oriented programming language, classes are your bread and butter. Classes are how you organize and think about your code, and they serve as your primary unit of encapsulation. You’ll be pleased to learn that TypeScript classes borrow heavily from C#, and support things like visibility modifiers, property initializers, polymorphism, decorators, and interfaces. But because TypeScript classes compile down to regular JavaScript classes, you can also express JavaScript idioms like mixins in a typesafe way.

Some of TypeScript’s class features, like property initializers and decorators, are supported by JavaScript classes too,¹ and so generate runtime code. Other features, like visibility modifiers, interfaces, and generics, are TypeScript-only features that just exist at compile time, and don’t generate any code when you compile your application to JavaScript.

In this chapter I’ll guide you through an extended example of how we work with classes in TypeScript, so that you can gain some intuition not only for TypeScript’s object-oriented language features, but for how and why we use them. Try to follow along, entering the code in your code editor as we go.

Classes and Inheritance

We’re going to build a chess engine. Our engine will model a game of chess and provide an API for two players to take turns making moves.

We’ll start by sketching out the types:

// Represents a chess game
class Game {}