TypeScript Comprehensive Guide – Table of Contents

1. Introduction to TypeScript

• What is TypeScript?
• Why TypeScript? Benefits over JavaScript
• TypeScript vs JavaScript
• Setting Up a TypeScript Project
• Running & Compiling TypeScript (tsc)

2. Basic Types and Type Inference, Annotations & Assertions

Basic Types

• string, number, boolean
• any, unknown, void, never
• Arrays and Tuples
• Enums
• Literal Types
• Type Aliases

Type Inference & Type Assertions

• Type Inference
• Type Annotations
• Type Assertions (Casting)
• Type Casting as vs angle-bracket syntax

3. Functions, Objects and Classes in TypeScript

Functions in TypeScript

• Function Types
• Optional & Default Parameters
• Rest Parameters
• Function Overloads
• this in Functions
• Arrow Functions
• Function Return Types
• Anonymous & Callback Functions

Objects & Interfaces

• Object Type Annotations
• Creating and Using Interfaces
• Optional and Readonly Properties
• Index Signatures
• Interface vs Type Alias
• Extending Interfaces
• Union & Intersection Types
• Nested Interfaces & Types
• Interface Merging
• Type Aliases for Functions & Objects
• Discriminated Unions

Classes in TypeScript

• Class Syntax
• Constructors & Access Modifiers (public, private, protected)
• Readonly & Static Members
• Getters and Setters
• Implementing Interfaces
• Inheritance and super()
• Abstract Classes
• Generics in Classes
• Parameter Properties
• Mixin in TypeScript

4. Advanced Types

• Union and Intersection Types
• Discriminated Unions
• Type Guards
• keyof, typeof, in Operators
• Mapped Types
• Conditional Types
• Template Literal Types

5. Generics

• Generic Functions
• Generic Interfaces & Types
• Constraints with Generics (extends)
• Default Type Parameters
• Utility Types (Partial, Required, Readonly, Record, etc.)

6. Modules and Namespaces

• ES Modules in TypeScript
• Import / Export Syntax
• Module Resolution
• Using TypeScript with Node.js / Deno
• Legacy Namespaces

7. Declaration Files

• What are .d.ts files?
• Writing Custom Type Declarations
• Using DefinitelyTyped (@types)
• Ambient Declarations

8. TypeScript and JavaScript Interop

• Type Checking JavaScript Files
• allowJs and checkJs
• Using JSDoc for Typing JS
• Migrating from JS to TS

9. Tooling & Configuration

• tsconfig.json Explained
• Strict Mode Options
• Useful Compiler Options
• Source Maps & Output Targets
• Integrating with Babel, Webpack, Vite

10. Working with Third-Party Libraries

• Typing External Libraries
• Using @types Packages
• Handling Untyped Modules
• Type Safety in APIs (like axios, fetch, etc.)

11. React + TypeScript

• Typing Functional Components
• Typing Props and State
• React Hooks with TypeScript
• Custom Hooks with Generics
• Context API with TypeScript

12. Node.js + TypeScript

• Setting up Node.js with TS
• Typing Express Apps
• Typing File System, Path, Process APIs
• Writing CLI Apps with TS

13. Advanced Topics

• Decorators in TypeScript
• TypeScript Compiler API
• AST Parsing and Transformation
• Performance Considerations

14. Best Practices

• Avoiding any
• Favoring unknown and never
• Structuring TypeScript Projects
• Consistent Naming Conventions
• Linting with ESLint + TypeScript

15. Testing in TypeScript

• TypeScript with Jest / Vitest
• Typing Mocks and Stubs
• Using ts-jest or other compilers

16. Troubleshooting and Debugging

• Common Type Errors
• Debugging with Source Maps
• Using VSCode IntelliSense
• Fixing Type Mismatches

17. Appendix

• Glossary of TypeScript Terms
• Cheatsheet of Common Types
• Useful Resources & Docs
• Community and Support