Master TypeScript Advanced Types for Robust Code

This skill provides guidance for TypeScript's advanced type system - generics, conditional types, mapped types, template literal types, and utility types - aimed at building robust, type-safe applications rather than relying on any or loose typing. Generics let a component or function stay reusable while still constraining its input/output shapes; conditional types let a type's shape depend on another type (useful for complex inference logic); mapped types transform an existing type into a new one field-by-field (the basis of many built-in utility types); template literal types constrain string-valued types to specific patterns; and utility types (built-in or custom) package common transformations - like making fields optional, readonly, or picking a subset - into reusable building blocks. The source itself is a high-level overview pointing to a companion resources/implementation-playbook.md for the detailed patterns and worked examples; the skill's role is to recognize when a task calls for this category of type-system work and apply the relevant best practices.

Use this skill when building type-safe libraries or frameworks, creating reusable generic components, implementing complex type inference logic, designing type-safe API clients, building form validation systems with compile-time guarantees, creating strongly-typed configuration objects, implementing type-safe state management, or migrating a JavaScript codebase to TypeScript and wanting to take advantage of its advanced type features rather than a minimal any-heavy port.

It is not the right skill for tasks unrelated to TypeScript's advanced type system, or for projects that need a different domain or tool entirely - basic TypeScript usage without generics, conditional types, or mapped types falls outside its specific focus.

Input is a TypeScript codebase or design problem that calls for advanced typing - a generic library API, a conditional type for inferring return shapes, a mapped type for transforming an existing interface, or a template literal type for constrained string patterns. Output is type-safe TypeScript code applying the appropriate advanced type feature, validated against the stated goal before being considered complete.

Points to a companion reference (resources/implementation-playbook.md) for detailed patterns and examples beyond what's summarized here.

TypeScript developers building type-safe libraries, frameworks, API clients, or migrating JavaScript codebases who need to reach for generics, conditional types, mapped types, or utility types rather than defaulting to loose or any typing.