ts-library_skill

Overview

This skill helps authors build production-ready TypeScript libraries with practical patterns for project setup, exports, build tooling, API design, testing, and releases. It distills conventions used by 20+ high-quality ecosystem libraries so you can adopt ESM-first, dual-format, and type-safe workflows quickly. Use it to standardize tooling and avoid common pitfalls when publishing packages.

How this skill works

The skill inspects common library concerns: package exports, tsconfig and module resolution, build tool choice (tsdown or unbuild), output formats, and test configuration. It recommends concrete file layouts, export maps, and build pipelines, and provides API design patterns (builder, factory, plugin) plus advanced type inference techniques. It also outlines CI/release workflows and test setups for reliable releases.

When to use it

• Starting a new TypeScript library (single package or monorepo)
• Configuring package.json exports for both CJS and ESM consumers
• Choosing a build toolchain (tsdown for typical libraries, unbuild for complex needs)
• Designing type-safe public APIs and advanced type inference
• Setting up vitest-based testing and automated release CI

Best practices

• Prefer ESM-first sources with dual outputs (ESM and CJS) and clear export maps
• Use moduleResolution: "Bundler" and strict tsconfig options for predictable types
• Keep runtime abstractions minimal; expose tree-shakeable APIs and mark sideEffects: false
• Choose tsdown for most builds; switch to unbuild when rollups, polyfills, or multiple targets are required
• Provide smart defaults and runtime environment detection rather than forcing user config

Example use cases

• Create a library that publishes both .mjs and .cjs builds while keeping accurate type declarations
• Design a plugin API with a factory pattern to preserve inference and extensibility
• Set up CI to run vitest, type checks, and automated release on tags
• Migrate an older CJS package to ESM-first while maintaining compatibility for consumers
• Structure a monorepo with consistent tsconfigs and per-package export maps