/ts-library

name: ts-library
description: Use when authoring TypeScript libraries or npm packages - covers project setup, package.json exports, build tooling (tsdown/unbuild), API design patterns, type inference tricks, testing, and publishing to npm. Use when bundling, configuring dual CJS/ESM output, or setting up release workflows.
license: MIT

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](references/project-setup.md) | | Package exports | [references/package-exports.md](references/package-exports.md) | | tsconfig options | [references/typescript-config.md](references/typescript-config.md) | | Build configuration | [references/build-tooling.md](references/build-tooling.md) | | ESLint config | [references/eslint-config.md](references/eslint-config.md) | | API design patterns | [references/api-design.md](references/api-design.md) | | Type inference tricks | [references/type-patterns.md](references/type-patterns.md) | | Testing setup | [references/testing.md](references/testing.md) | | Release workflow | [references/release.md](references/release.md) | | CI/CD setup | [references/ci-workflows.md](references/ci-workflows.md) |

Loading Files

**Consider loading these reference files based on your task:**

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

New Library Workflow

1. Create project structure → load [references/project-setup.md](references/project-setup.md) 2. Configure `package.json` exports → load [references/package-exports.md](references/package-exports.md) 3. Set up build with tsdown → load [references/build-tooling.md](references/build-tooling.md) 4. Verify build: `pnpm build && pnpm pack --dry-run` — check output includes `.mjs`, `.cjs`, `.d.ts` 5. Add tests → load [references/testing.md](references/testing.md) 6. Configure release → load [references/release.md](references/release.md)

Quick Start

// package.json (minimal)
{
  "name": "my-lib",
  "type": "module",
  "exports": {
    ".": {
      "import": "./dist/index.mjs",
      "require": "./dist/index.cjs"
    }
  },
  "main": "./dist/index.cjs",
  "module": "./dist/index.mjs",
  "types": "./dist/index.d.ts",
  "files": ["dist"]
}

// tsdown.config.ts
import { defineConfig } from 'tsdown'

export default defineConfig({
  entry: ['src/index.ts'],
  format: ['esm', 'cjs'],
  dts: true,
})

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_