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Hectal

TypeScript · JavaScript with types, checked before it runs

Learn TypeScript properly,
from your first type to TypeScript 7.

Start from why TypeScript exists: you need only some JavaScript, and every word is explained in plain English. You will learn annotations and inference, functions, objects and interfaces, unions and narrowing, enums and tuples, classes and decorators, generics, keyof, mapped, conditional and template literal types, utility types and type-level patterns, modules and declaration files, every important tsconfig option, TypeScript with the DOM and with React, real project tooling, and how the checker thinks. Every example is checked by the real TypeScript compiler in your browser and verified against TypeScript 7, so the errors you see are exactly what tsc prints, and every phase ends with exercises the compiler checks for you.

Start from zero The full roadmap
Phases
18
Topics
109
Hours
44
Diagrams
100
Exercises
720

By the end you can

What this course makes you able to do

  • Type everyday JavaScript: values, functions, objects, arrays and classes, and read every tsc error
  • Model data with unions, discriminated unions and narrowing so impossible states can't be written
  • Write generic functions and types, and build your own utility types with keyof, mapped, conditional and template literal types
  • Set up real projects: tsconfig and strictness, modules and declaration files, Node, Vite and TypeScript 7
  • Type the DOM, async code, API data and React components safely
  • Answer advanced TypeScript interview questions and solve type challenges live

Beginner → Advanced

The curriculum, by level

Beginner
  1. 0Start Here: Why TypeScript4 topics · ~80 min
  2. 1Basic Types and Annotations7 topics · ~2 h
  3. 2Functions7 topics · ~3 h
  4. 3Type Aliases and Interfaces6 topics · ~2 h
  5. 4Unions, Literals and Narrowing7 topics · ~3 h
  6. 5Arrays, Tuples, Enums and Special Types6 topics · ~3 h
Intermediate
  1. 6Classes and Object-Oriented TypeScript8 topics · ~3 h
  2. 7Generics7 topics · ~3 h
  3. 8Type Operators5 topics · ~2 h
  4. 11Modules and Declaration Files6 topics · ~2 h
  5. 12The Compiler and tsconfig6 topics · ~2 h
  6. 13TypeScript in the Browser: DOM and Async6 topics · ~2 h
  7. 14TypeScript with React6 topics · ~2 h
  8. 15TypeScript in Real Projects6 topics · ~3 h
Advanced
  1. 9Conditional and Template Literal Types5 topics · ~2 h
  2. 10Utility Types and Type-Level Patterns6 topics · ~2 h
  3. 16Advanced TypeScript6 topics · ~2 h
  4. 17Interviews and Capstone5 topics · ~3 h

Where should I start?

Pick a path for your goal

Complete beginner

You know some JavaScript and no TypeScript. Start here: every word is explained.

  1. 10 · Start Here: Why TypeScript
  2. 21 · Basic Types and Annotations
  3. 32 · Functions
  4. 43 · Type Aliases and Interfaces
  5. 54 · Unions, Literals and Narrowing
  6. 65 · Arrays, Tuples, Enums and Special Types

Job-ready TypeScript developer

You can type basic code and want what teams expect day to day.

  1. 16 · Classes and Object-Oriented TypeScript
  2. 27 · Generics
  3. 311 · Modules and Declaration Files
  4. 412 · The Compiler and tsconfig
  5. 513 · TypeScript in the Browser: DOM and Async
  6. 614 · TypeScript with React
  7. 715 · TypeScript in Real Projects

Advanced types and interviews

You use TypeScript daily and want type-level skills and interview depth.

  1. 18 · Type Operators
  2. 29 · Conditional and Template Literal Types
  3. 310 · Utility Types and Type-Level Patterns
  4. 416 · Advanced TypeScript
  5. 517 · Interviews and Capstone