stack/v1/packages/mosaic/framework/skills/antfu/references/library-development.md

name, description

name	description
library-development	Building and publishing TypeScript libraries with tsdown. Use when creating npm packages, configuring library bundling, or setting up package.json exports.

Library Development

Aspect	Choice
Bundler	tsdown
Output	Pure ESM only (no CJS)
DTS	Generated via tsdown
Exports	Auto-generated via tsdown

tsdown Configuration

Use tsdown with these options enabled:

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

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

Option	Value	Purpose
format	['esm']	Pure ESM, no CommonJS
dts	true	Generate .d.ts files
exports	true	Auto-update exports field in package.json

Multiple Entry Points

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

The exports: true option auto-generates the exports field in package.json when running tsdown.

---

package.json

Required fields for pure ESM library:

{
  "type": "module",
  "main": "./dist/index.mjs",
  "module": "./dist/index.mjs",
  "types": "./dist/index.d.mts",
  "files": ["dist"],
  "scripts": {
    "build": "tsdown",
    "prepack": "pnpm build",
    "test": "vitest",
    "release": "bumpp -r"
  }
}

The exports field is managed by tsdown when exports: true.

prepack Script

For each public package, add "prepack": "pnpm build" to scripts. This ensures the package is automatically built before publishing (e.g., when running npm publish or pnpm publish). This prevents accidentally publishing stale or missing build artifacts.