Programming TypeScript

Chapter 2. TypeScript: A 10_000 Foot View

Over the next few chapters, I’ll introduce the TypeScript language, give you an overview of how the TypeScript Compiler (TSC) works, and take you on a tour of TypeScript’s features and the patterns you can develop with them. We’ll start with the compiler.

The Compiler

Depending on what programming languages you worked with in the past (that is, before you decided to buy this book and commit to a life of type safety), you’ll have a different understanding of how programs work. The way TypeScript works is unusual compared to other mainstream languages like JavaScript or Java, so it’s important that we’re on the same page before we go any further.

Let’s start broad: programs are files that contain a bunch of text written by you, the programmer. That text is parsed by a special program called a compiler, which transforms it into an abstract syntax tree (AST), a data structure that ignores things like whitespace, comments, and where you stand on the tabs versus spaces debate. The compiler then converts that AST to a lower-level representation called bytecode. You can feed that bytecode into another program called a runtime to evaluate it and get a result. So when you run a program, what you’re really doing is telling the runtime to evaluate the bytecode generated by the compiler from the AST parsed from your source code. The details vary, but for most languages this is an accurate high-level view.

Once again, the steps are:

1. Program is parsed ...