Publish types and build output

TypeScript source is for maintainers. Consumers need JavaScript their runtime can execute plus type declarations (.d.ts files) if they use TypeScript.

For @acme/slugify-title, we author src/index.ts and publish compiled output in dist/.

Build JavaScript and declarations together

tsup.config.ts:

import { defineConfig } from 'tsup'

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

Run:

npm run build
ls dist

You should see files such as:

index.js
index.cjs
index.d.ts
index.js.map

Point exports at those files, not at src/:

{
  "exports": {
    ".": {
      "import": "./dist/index.js",
      "require": "./dist/index.cjs",
      "types": "./dist/index.d.ts"
    }
  }
}

Verify from the consumer fixture

In your TypeScript smoke project:

import { slugifyTitle } from '@acme/slugify-title'

const slug: string = slugifyTitle('Hello World!')

Run npx tsc --noEmit. If types resolve, TypeScript found index.d.ts through the types condition in exports.

Common failure: exports aim at missing files

If you rename a build output but forget package.json, Node fails at runtime and TypeScript fails in the editor. After every build config change, run the consumer fixture again.

Pure JavaScript libraries can skip a compile step and publish src/ directly. The moment you add TypeScript or non-standard syntax, a build step becomes part of the public contract.

Break one path on purpose once

Delete dist/index.d.ts, run the consumer TypeScript check, and read the error:

Could not find a declaration file for module '@acme/slugify-title'

That is what your users see when declarations are missing from the tarball. Add a CI step that fails on that error so it never ships again.

Source maps in dist/ help consumers debug minified or compiled output. They are optional for tiny libraries, but I include them when the compiled JS is hard to read.

Keep tsconfig.json strict enabled for library code. A loose type inside the package becomes a loose type in every project that installs it.

See Build and publish a TypeScript package to npm for a full walkthrough with dual ESM and CJS outputs.