typescript-advanced-types

name	typescript-advanced-types
description	Master TypeScript's advanced type system — generics, conditional types, mapped types, template literals, and utility types — for building type-safe Angular 21.x components, NestJS 11.x APIs, and MCP Builder integrations. Use when implementing complex type inference, type-safe API clients, branded types, DeepPartial/DeepReadonly patterns, or migrating JS to TS.
allowed-tools	Read
metadata	{"triggers":"Generic types, Conditional types, Mapped types, Utility types, Template literal types, Type-safe API client, Type-safe form, DeepPartial, DeepReadonly, Branded types, type inference","related-skills":"nestjs-api, angular-spa, mcp-builder, nestjs-coding-standard, typescript-expert, typescript-pro","domain":"backend","role":"specialist","scope":"implementation","output-format":"code","risk":"safe","source":"antigravity-awesome-skills (community)","date_added":"2026-03-14"}
last-reviewed	2026-03-14

TypeScript Advanced Types

Iron Law: Before applying any type pattern, READ the actual TypeScript file first. Do not suggest type changes from memory — verify the actual code (file:line) before making any claim.

When to Use

• 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

Do Not Use

• The task is unrelated to TypeScript advanced types
• You need a different domain or tool outside this scope (Flutter/Dart, Java, Python)

Core Type Patterns

1. Generics

Create reusable, type-flexible components while maintaining type safety. Use generic constraints (T extends HasLength) to narrow what types are accepted. Supports multiple type parameters, default types, and conditional constraints. See playbook §1 for examples.

2. Conditional Types

Create types that depend on conditions: T extends string ? true : false. Supports infer for extracting type components (e.g., return type, promise type, array element type). Distributive conditional types apply over union members automatically. See playbook §2 for examples.

3. Mapped Types

Transform existing types by iterating over their properties with [P in keyof T]. Supports modifiers (readonly, ?), key remapping via as, and filtering properties by type. Enables patterns like Partial<T>, Readonly<T>, and Getters<T>. See playbook §3 for examples.

4. Template Literal Types

Create string-based types with pattern matching: `on${Capitalize<EventName>}`. Enables type-safe event names, path builders, getter/setter name generation. Built-in helpers: Uppercase, Lowercase, Capitalize, Uncapitalize. See playbook §4 for examples.

5. Utility Types

TypeScript's built-in transformation utilities: Partial<T>, Required<T>, Readonly<T>, Pick<T,K>, Omit<T,K>, Exclude<T,U>, Extract<T,U>, NonNullable<T>, Record<K,T>. Combine with custom mapped types for DeepPartial<T> and DeepReadonly<T>. See playbook §5 and Pattern 4 for examples.

Tech Stack Applicability

Stack	Applicable	Notes
Angular 21.x	Yes	Type-safe forms, component inputs, RxJS operator types, signal types
NestJS 11.x	Yes	Type-safe DTOs, guards, interceptors, Prisma query result types
MCP Builder (TypeScript)	Yes	Type-safe tool definitions, request/response contracts
Flutter / Dart	No	Dart has its own type system — use the flutter-mobile skill
Java / Spring Boot	No	Java generics differ significantly — use the java-spring-api skill
Python / FastAPI	No	Use Pydantic models via the python-dev skill

Resources

resources/implementation-playbook.md contains full patterns, checklists, and code samples covering:

• Core Concepts: Generics, Conditional Types, Mapped Types, Template Literal Types, Utility Types
• Advanced Patterns:
  • Pattern 1: Type-Safe Event Emitter
  • Pattern 2: Type-Safe API Client
  • Pattern 3: Builder Pattern with Type Safety
  • Pattern 4: Deep Readonly / Deep Partial
  • Pattern 5: Type-Safe Form Validation
  • Pattern 6: Discriminated Unions
• Type Inference Techniques: infer keyword, Type Guards, Assertion Functions
• Best Practices: 10 rules including unknown over any, strict mode, type testing
• Common Pitfalls and Performance Considerations

Related Skills

Combine With	When
nestjs-api	Typing NestJS DTOs, guards, interceptors, Prisma result shapes with advanced utility types
angular-spa	Typing Angular reactive forms, component inputs/outputs, RxJS pipe operators
mcp-builder	Defining type-safe tool schemas, strongly-typed request/response contracts for MCP tools