ts-library

Define an exports map with types, import, and require conditions pointing to .d.mts, .mjs, and .cjs files, keeping types first. Also set main, module, and types as fallbacks, and mark sideEffects as false for tree-shaking.

tsdown is recommended for most libraries because it is fast and simple, with dts generation and glob entries. unbuild suits complex builds, Nuxt modules, and cases needing automatic externals handling.

Use Bundler for libraries consumed by bundlers like Vite or webpack, since it allows extensionless imports and supports the exports field. Use Node16 or NodeNext for Node.js-only libraries requiring explicit .js extensions.

Use OIDC trusted publishing: grant id-token write permission, run on Node.js 24 or later, add registry-url to setup-node, include a repository field in package.json, and publish with the --provenance flag after configuring the trusted publisher on npmjs.com.

Type resolution fails when declaration files are missing, condition order is wrong, or moduleResolution mismatches. Validate the package with publint and @arethetypeswrong/cli, and enable dts generation in your build config.

Enable vitest typecheck and write expectTypeOf assertions in test-d files. For multi-version coverage, add a CI matrix that installs typescript at versions like 5.0 through 5.8 and runs typecheck for each.