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TypeScript

Quick reference for TypeScript types, interfaces, and advanced features

10 min read
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Basic Types

Primitive Types

TypeScript basic primitive types and type annotations

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💡 Use unknown instead of any when possible
📌 const assertions create readonly literal types
✅ Enable strictNullChecks for better null safety

Type Aliases & Unions

Create custom type aliases and union types for flexibility

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💡 Use discriminated unions for exhaustive checks
⚡ Type aliases improve code readability
📌 Template literal types for string manipulation

Functions

Function Types

Type annotations for functions and their parameters

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💡 Use optional parameters instead of overloads when possible
📌 Arrow functions preserve lexical this
✅ Always type function parameters

Function Overloading

Define multiple function signatures for different parameter types

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⚠️ Overload signatures must be compatible with implementation
💡 Order overloads from most specific to least specific
📌 Consider union types instead of overloads

Interfaces & Classes

Interfaces

Define object shapes and contracts for type checking

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💡 Interfaces can be extended and merged
📌 Use interfaces for object shapes
✅ Prefer interfaces over type aliases for objects

Classes

Object-oriented programming with TypeScript classes

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💡 Use parameter properties to reduce boilerplate
🔒 Private fields start with # in modern TS
📌 Abstract classes cannot be instantiated

Inheritance

Class inheritance and method overriding in TypeScript

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💡 Use super() to call parent constructor
📌 Protected members accessible in derived classes
✅ Mixins provide multiple inheritance pattern

Generics

Generic Functions

Create reusable functions that work with multiple types

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💡 TypeScript often infers generic types automatically
📌 Use constraints to limit generic types
✅ Generics make code reusable and type-safe

Generic Classes & Interfaces

Build flexible classes and interfaces with generic types

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💡 Generic classes create type-safe data structures
📌 Static methods can have their own generic parameters
✅ Use generic constraints for type safety

Advanced Types

Utility Types

Built-in TypeScript utility types for type transformations

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💡 Utility types reduce boilerplate code
⚡ Combine utility types for complex transformations
📌 Most utility types work with generics

Type Guards

Runtime checks that narrow types within conditional blocks

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💡 Type guards narrow types in conditional branches
📌 Custom type guards use "is" syntax
✅ Assertion functions throw or narrow types

Mapped & Conditional Types

Transform and conditionally create types based on other types

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💡 Mapped types transform properties of existing types
⚡ Conditional types enable type-level programming
📌 infer keyword extracts types in conditions

Modules & Namespaces

Imports & Exports

ES6 module syntax for importing and exporting code

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💡 Use type-only imports for better tree-shaking
📌 Dynamic imports for code splitting
✅ Re-export to create public API

Declaration Files

Type declarations for JavaScript libraries and modules

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💡 Use @types packages for library types
📌 .d.ts files contain only type declarations
✅ Declare modules for assets and untyped packages

TSConfig Reference

Compiler Options Reference

Complete reference of TypeScript compiler options with descriptions and values

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💡 Start with strict: true and adjust as needed
📌 Use paths for clean import aliases
⚡ skipLibCheck speeds up compilation significantly
✅ Different project types need different configs