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From Ruby to TypeScript

A Ruby Programmer's Guide to Learning TypeScript

From Ruby to TypeScript
This book is 100% completeLast updated on 2026-11-01
Joel Bryan Juliano

This book is built on one idea: the fastest way for a Rubyist to learn TypeScript is to map every TypeScript concept back to Ruby. Each chapter starts with Ruby code you already understand, then shows the TypeScript equivalent. You’re not learning from scratch — you’re translating.

Take everything you know about Ruby — classes, hashes, exceptions, enumerable methods, blocks — and translate it directly to TypeScript. No fluff, no abstract theory, just runnable Ruby-to-TypeScript comparisons with hands-on exercises.

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About

About

About the Book

Learning a new programming language is hard. Learning one that adds a whole type system on top of JavaScript — while also introducing async/await, a new module system, and a different runtime — is harder.

From Ruby to TypeScript skips the abstract theory and teaches TypeScript the way a Rubyist actually learns: by mapping every TypeScript concept back to Ruby. console.log replaces puts. Template literals replace string interpolation. interface replaces duck typing. async/await replaces threads and fibers. try/catch replaces begin/rescue. And types — the biggest mental shift — are introduced step by step, with Ruby analogies at every turn.

Each chapter starts with Ruby code you already understand, then shows the TypeScript equivalent — complete, runnable, and explained line by line. You'll build types, classes, interfaces, async pipelines, and generics from the ground up, with hands-on exercises at every step.

TypeScript has become the lingua franca of modern web development. React, Next.js, Angular, Vue, Deno, Bun, VS Code — all built with TypeScript. Companies like Airbnb, Shopify, Slack, and Microsoft run it in production at scale. It has been battle-tested and proven — a mature, powerful language to build your career on.

Updated for TypeScript 5.x, this edition covers strict mode, ES modules, async/await, discriminated unions, utility types, generics, Zod validation, and the modern toolchain (tsx, ts-node, vitest) — everything you need to write production TypeScript in 2026.

This book was written with a Rubyist in mind. Every learning metaphor is based on Ruby. If you know Ruby and want to add TypeScript to your toolkit — for full-stack development, backend services, or your next career move — this is the book.

Take the Course

Want to go further? The companion course turns this book into a guided learning path with chapter quizzes, a final exam and a certificate of completion: From Ruby to TypeScript: The Course

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Author

About the Author

Joel Bryan Juliano

Hi, I'm Joel.

I am Dutch-Filipino Software Engineer with 20+ years of experience.

And with over 20 years in the game, I’ve seen it all and loved every minute of it.

My journey has taken me through a variety of industries, from sports streaming to cybersecurity, both in the private sector and for the Dutch government, and everything in between.

Along the way, I’ve picked up a diverse set of skills and experiences, in which I document into books.

Contents

Table of Contents

Preface

Introduction

  1. Who This Book Is For
  2. How to Use This Book
  3. What This Book Is Not
  4. A Note on Runtime
  5. About the Author

Chapter 1: Getting Started

  1. Installing Node.js and a TypeScript Runner
  2. Your First TypeScript Program
  3. Template Literals: String Interpolation
  4. Variables: const and let
  5. Type Annotations (Your First Taste)
  6. Functions
  7. Arrow Functions
  8. The Entry Point
  9. tsconfig.json: Project Configuration
  10. Chapter Exercises
  11. Summary

Chapter 2: Types & Type Annotations

  1. The Basic Types
  2. Type Annotations
  3. Type Inference
  4. null and undefined
  5. Union Types
  6. Literal Types and Enums
  7. Type Aliases
  8. any and unknown
  9. Type Assertions
  10. Chapter Exercises
  11. Summary

Chapter 3: Arrays, Tuples & Iteration

  1. Typed Arrays
  2. Mixed-Type Arrays
  3. Tuples
  4. readonly Arrays and Tuples
  5. Iteration: for…of (The Each Replacement)
  6. forEach: Each with an Index
  7. Traditional for Loop (C-Style)
  8. map: Transform Every Element
  9. filter: Select Elements
  10. reduce: Aggregate Values
  11. some and every: Predicate Checks
  12. Spread and Rest: The Splat Operator
  13. Chapter Exercises
  14. Summary

Chapter 4: Objects, Records & Maps

  1. Object Types: The Hash Replacement
  2. Optional Properties
  3. Index Signatures: Hash-Like Objects
  4. Record: Typed Hash
  5. Map: When Keys Are Dynamic
  6. Set: Unique Collections
  7. Object Destructuring: Hash Splat
  8. Spread: Merging Objects
  9. readonly Properties
  10. Chapter Exercises
  11. Summary

Chapter 5: Functions Deep Dive

  1. Function Declarations vs Arrow Functions
  2. Typed Parameters and Return Types
  3. Optional and Default Parameters
  4. Rest Parameters: Ruby’s Splat
  5. Callbacks and Function Types
  6. Void and Never Return Types
  7. Function Overloads
  8. Chapter Exercises
  9. Summary

Chapter 6: Classes

  1. A Ruby Class, Translated
  2. Access Modifiers: public, private, protected
  3. JavaScript Private Fields (#)
  4. Parameter Properties (Shorthand)
  5. Inheritance: extends
  6. Abstract Classes
  7. Getters and Setters
  8. this and Arrow Functions
  9. Chapter Exercises
  10. Summary

Chapter 7: Interfaces & Type Aliases

  1. Interfaces: The Basics
  2. interface vs type
  3. Extending Interfaces
  4. Optional and readonly Properties in Interfaces
  5. Index Signatures in Interfaces
  6. Structural Typing in Practice
  7. When Interfaces Feel Like Ruby Modules
  8. Chapter Exercises
  9. Summary

Chapter 8: Modules & Package Management

  1. import and export: The New require
  2. Named Exports vs Default Exports
  3. Re-exports and Barrel Files
  4. package.json: The Gemfile
  5. npm, Yarn, and pnpm
  6. node_modules and the Magic of Resolution
  7. Your First TypeScript Project (Walkthrough)
  8. tsconfig.json Paths: Module Aliases
  9. Installing Type Definitions
  10. Chapter Exercises
  11. Summary

Chapter 9: Error Handling

  1. try/catch/finally: The Direct Mapping
  2. Typed Catch with instanceof
  3. Custom Error Classes
  4. The TypeScript Way: Errors as Values
  5. Strict Null Checks: Eliminating NoMethodError on nil
  6. Optional Chaining: Safe Navigation
  7. Nullish Coalescing: The || Alternative
  8. Chapter Exercises
  9. Summary

Chapter 10: Async Programming

  1. The Event Loop
  2. Callbacks and Callback Hell
  3. Promises: The Foundation
  4. async/await: Write Async Code That Looks Synchronous
  5. The async Main Function
  6. Async Iteration
  7. Ruby Threads vs TypeScript Promises
  8. Chapter Exercises
  9. Summary

Chapter 11: JSON & Type Narrowing

  1. JSON.stringify: Value to JSON
  2. JSON.parse: JSON to Value (and the any Problem)
  3. Type Assertions: Trust Me
  4. Type Guards: Prove It at Runtime
  5. Zod: Schema Validation
  6. Discriminated Unions: The JSON Pattern
  7. Working with Unknown JSON Shapes
  8. Chapter Exercises
  9. Summary

Chapter 12: Generics & Utility Types

  1. The Problem Generics Solve
  2. Generic Functions
  3. Generic Interfaces and Types
  4. Generic Constraints
  5. Built-in Utility Types
  6. Generics vs Duck Typing
  7. Chapter Exercises
  8. Summary

Appendix A: Ruby ↔ TypeScript Quick Reference

  1. Syntax & Structure
  2. Variables & Types
  3. Data Structures
  4. Functions & Methods
  5. Error Handling
  6. Concurrency & Async
  7. Modules & Packages
  8. Common Patterns
  9. TypeScript CLI Cheat Sheet
  10. File Layout

Appendix B: Exercise Answers

  1. Chapter 1
  2. Chapter 2
  3. Chapter 3
  4. Chapter 4
  5. Chapter 5
  6. Chapter 8
  7. Chapter 9
  8. Chapter 10
  9. Chapter 11
  10. Chapter 12

Glossary

Acknowledgements

Credits

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