Programming TypeScript

Chapter 1. Introduction

So, you decided to buy a book about TypeScript. Why?

Maybe it’s because you’re sick of those weird cannot read property blah of undefined JavaScript errors. Or maybe you heard TypeScript can help your code scale better, and wanted to see what all the fuss is about. Or you’re a C# person, and have been thinking of trying out this whole JavaScript thing. Or you’re a functional programmer, and decided it was time to take your chops to the next level. Or your boss was so fed up with your code causing production issues that they gave you this book as a Christmas present (stop me if I’m getting warm).

Whatever your reasons are, what you’ve heard is true. TypeScript is the language that will power the next generation of web apps, mobile apps, NodeJS projects, and Internet of Things (IoT) devices. It will make your programs safer by checking for common mistakes, serve as documentation for yourself and future engineers, make refactoring painless, and make, like, half of your unit tests unnecessary (“What unit tests?”). TypeScript will double your productivity as a programmer, and it will land you a date with that cute barista across the street.

But before you go rushing across the street, let’s unpack all of that a little bit, starting with this: what exactly do I mean when I say “safer”? What I am talking about, of course, is type safety.

Type safety

Using types to prevent programs from doing invalid things.¹

Here are a few examples of things that are invalid: ...