typescript-advanced-types

TypeScript Advanced Types

Guidance for mastering TypeScript's advanced type system — generics, conditional types, mapped types, template literal types, utility types, inference, and type guards — for building robust, type-safe applications.

When to Use This Skill

• Building type-safe libraries or frameworks
• Creating reusable generic components
• Implementing complex type inference logic
• Designing type-safe API clients
• Building form validation systems
• Creating strongly-typed configuration objects
• Implementing type-safe state management
• Migrating JavaScript codebases to TypeScript

How to Use

This file is a thin index. Identify which topic the task needs from the decision tree below, then Read the matching references/<topic>.md file for the detailed patterns and code. Load only the references you need; for a broad task you may read several.

Decision Tree

• Need a reusable, type-flexible function/class/component (type parameters, constraints, builders, event emitters)? → references/generics.md
• Need a type that branches on a condition (T extends U ? X : Y, distributive types, API client signatures)? → references/conditional-types.md
• Need to transform an existing type's properties (readonly/partial, key remapping, filtering, deep transforms, form validation shapes)? → references/mapped-types.md
• Need string-based types (event handler names, path strings, Uppercase/Capitalize)? → references/template-literal-types.md
• Need built-in helpers (Partial, Pick, Omit, Record, Exclude), discriminated unions, type testing, best practices, pitfalls, or performance notes? → references/utility-types.md
• Need to extract/infer a type from another (infer keyword, element/promise/parameter types)? → references/inference.md
• Need runtime narrowing (type guards, value is T, asserts value is T)? → references/type-guards.md

Topic Reference Map

Topic	Read this file	Covers
Generics	references/generics.md	Generic functions, constraints, multiple type params, typed event emitter, type-safe builder
Conditional types	references/conditional-types.md	Basic/nested/distributive conditionals, infer return types, type-safe API client
Mapped types	references/mapped-types.md	Readonly/partial/optional, key remapping, property filtering, deep readonly/partial, form validation
Template literal types	references/template-literal-types.md	Template literals, string manipulation, recursive path building
Utility types	references/utility-types.md	Built-in utilities, discriminated unions, type testing, best practices, pitfalls, performance
Inference	references/inference.md	infer keyword — element, promise, and parameter extraction
Type guards	references/type-guards.md	User-defined type guards and assertion functions

Best Practices (summary)

Use unknown over any; prefer interface for object shapes and type for unions; lean on inference; build reusable helper types; use const assertions; prefer type guards over assertions; enable strict mode; test your types. Full list with pitfalls and performance considerations lives in references/utility-types.md.