advanced-types_skill

Overview

This skill teaches advanced TypeScript type features including generics, conditional types, mapped types, and utility types. It focuses on practical patterns for building robust, type-safe APIs and libraries. You will learn how to model complex data, infer types, and perform type-level computation to reduce runtime errors.

How this skill works

The skill inspects and explains advanced type constructs with examples and patterns: generic functions and classes, conditional and distributive types, key remapping in mapped types, and built-in utility types. It shows how to compose and extend types, create custom utilities, and apply type-level programming techniques such as branded or opaque types. Each concept includes constraints, common pitfalls, and idiomatic usage.

When to use it

• When you need precise compile-time modeling of complex data structures
• When building reusable libraries or public APIs that require strong type guarantees
• When reducing runtime checks by moving validation to the type system
• When creating helper utility types to simplify repetitive typings
• When optimizing developer DX with better autocompletion and error messages

Best practices

• Prefer simple, readable types; only escalate to complex conditional or recursive types when necessary
• Use constraints and default type parameters to guide generic usage and provide sensible fallbacks
• Favor built-in utility types (Partial, Pick, Record) before reinventing equivalents
• Document nontrivial type-level behavior and provide runtime guards for safety when types are complex
• Limit deeply recursive or highly distributive types to avoid compiler performance regressions

Example use cases

• Create a typed API client that infers response shapes and maps endpoints to return types
• Build a form library that derives input props from a schema using mapped and conditional types
• Define branded or opaque types to prevent accidental mixing of distinct ID types (e.g., UserId vs OrderId)
• Implement advanced helpers like DeepReadonly, Merge, or PickByValue for library utilities
• Write variadic tuple utilities to type-safe middleware chains or argument transforms