A pragmatic guide for those who already know JavaScript
By Claude Code (Sonnet 4.5)
You're a JavaScript developer. You've shipped features, debugged async nightmares, and probably have strong opinions about semicolons. Now you're here because TypeScript is everywhere, and you're tired of pretending .d.ts files make sense.
This book won't teach you what variables are or how loops work. Instead, it maps the JavaScript you know onto TypeScript's type system, showing you exactly what changes, what stays the same, and where the real power lies.
- JavaScript developers who want to learn TypeScript properly (not just add
anyeverywhere) - Engineers evaluating TypeScript for their team
- Developers who started with TypeScript but want to understand the "why" behind the syntax
- Anyone who's tired of runtime errors that types could have caught
- How TypeScript's type system actually works (and where it doesn't)
- The TypeScript toolchain: compilers, configs, and development workflow
- Practical patterns for functions, objects, and modules
- Generics without the academic overhead
- Advanced type manipulation techniques
- Integrating TypeScript with modern frameworks and libraries
- Migration strategies for existing JavaScript codebases
- Why TypeScript Exists (and why you're here)
- The Type System You Already Know
- Your TypeScript Toolchain
- Functions: Where Things Get Interesting
- Interfaces, Types, and the Art of Shapes
- Generics (or: How I Learned to Stop Worrying and Love <T>)
- Advanced Types and the Compiler's Bag of Tricks
- Classes and OOP (Yes, Really)
- Modules, Namespaces, and Declaration Files
- The TypeScript Ecosystem
- Migrating JavaScript to TypeScript
- TypeScript in the Wild (React, Node, and Beyond)
This book treats you like an adult who can read documentation. Instead of exhaustive API references, it focuses on mental models, practical patterns, and the "gotchas" that only emerge from real-world use.
TypeScript is a tool, not a religion. Sometimes the types help. Sometimes they get in the way. You'll learn when to embrace them and when to tell the compiler to trust you.
Found an error? Have a suggestion? Open an issue or PR. This book is open source because the best technical writing is collaborative.
MIT - See LICENSE file for details
Ready? Let's start with Chapter 1: Why TypeScript Exists.