TypeScript Library Development

Patterns for authoring high-quality TypeScript libraries, extracted from studying unocss, shiki, unplugin, vite, vitest, vueuse, zod, trpc, drizzle-orm, and more.

When to Use

• Starting a new TypeScript library (single or monorepo)
• Setting up package.json exports for dual CJS/ESM
• Configuring tsconfig for library development
• Choosing build tools (tsdown, unbuild)
• Designing type-safe APIs (builder, factory, plugin patterns)
• Writing advanced TypeScript types
• Setting up vitest for library testing
• Configuring release workflow and CI

For Nuxt module development: use nuxt-modules skill

Quick Reference

Working on...	Load file
New project setup	references/project-setup.md
Package exports	references/package-exports.md
tsconfig options	references/typescript-config.md
Build configuration	references/build-tooling.md
ESLint config	references/eslint-config.md
API design patterns	references/api-design.md
Type inference tricks	references/type-patterns.md
Testing setup	references/testing.md
Release workflow	references/release.md
CI/CD setup	references/ci-workflows.md

Loading Files

Consider loading these reference files based on your task:

• [ ] references/project-setup.md - if starting a new TypeScript library project
• [ ] references/package-exports.md - if configuring package.json exports or dual CJS/ESM
• [ ] references/typescript-config.md - if setting up or modifying tsconfig.json
• [ ] references/build-tooling.md - if configuring tsdown, unbuild, or build scripts
• [ ] references/eslint-config.md - if setting up ESLint for library development
• [ ] references/api-design.md - if designing public APIs, builder patterns, or plugin systems
• [ ] references/type-patterns.md - if working with advanced TypeScript types or type inference
• [ ] references/testing.md - if setting up vitest or writing tests for library code
• [ ] references/release.md - if configuring release workflow or versioning
• [ ] references/ci-workflows.md - if setting up GitHub Actions or CI/CD pipelines

DO NOT load all files at once. Load only what's relevant to your current task.

Key Principles

• ESM-first: "type": "module" with .mjs outputs
• Dual format: always support both CJS and ESM consumers
• moduleResolution: "Bundler" for modern TypeScript
• tsdown for most builds, unbuild for complex cases
• Smart defaults: detect environment, don't force config
• Tree-shakeable: lazy getters, proper sideEffects: false

Token efficiency: Main skill ~300 tokens, each reference ~800-1200 tokens