Dual Publish

• Tested on projects with 16M downloads per month.
• CI tests show it working with Node.js, browsers, React Native,
  bundlers (webpack, Parcel, Rollup, or esbuild) and CDNs (like jspm).
• Does not change line numbers in stacktrace and keeps sources readable.
• No build step. No need for separated src/ and dist/ directories in the repository. You will be able to test a branch by installing a version from GitHub: npm i example@you/example#fix.
• Multiple files support. Your users will be able to import separated files via import { nanoid } from 'nanoid/async'.
• Cleans npm package from development configs before publishing.
• Supports process.env.NODE_ENV for development checks, which you would want to remove in a production JS bundle.

You write CommonJS in your npm library sources:

// index.js
module.exports = { lib }

npx dual-publish compiles your library when publishing to npm:

// index.js
export { lib }

// index.cjs
module.exports = { lib }

// package.json
{
  …
  "type": "module",
  "module": "index.js",
  "main": "index.cjs",
  "exports": {
    "require": "./index.cjs",
    "import": "./index.js"
  }
}

Now your library can be imported natively as ESM or CommonJS:

// CommonJS
let { lib } = require('lib')

// ESM in Node.js, webpack, Parcel, and Rollup
import { lib } from 'lib'

// ESM in browser
import { lib } from 'https://cdn.jsdelivr.net/npm/lib/index.js'