How to publish a module written in ES6 to NPM?

Question

I was about to publish a module to NPM, when I thought about rewriting it in ES6, to both future-proof it, and learn ES6. I\'ve used Babel to transpile to ES5, and run tests

Answer 1

Node.js 13.2.0+ supports ESM without the experimental flag and there're a few options to publish hybrid (ESM and CommonJS) NPM packages (depending on the level of backward compatibility needed): https://2ality.com/2019/10/hybrid-npm-packages.html

I recommend going the full backward compatibility way to make the usage of your package easier. This could look as follows:

The hybrid package has the following files:

mypkg/
  package.json
  esm/
    entry.js
  commonjs/
    package.json
    entry.js

mypkg/package.json

{
  "type": "module",
  "main": "./commonjs/entry.js",
  "exports": {
    "./esm": "./esm/entry.js"
  },
  "module": "./esm/entry.js",
  ···
}

mypkg/commonjs/package.json

{
  "type": "commonjs"
}

Importing from CommonJS:

const {x} = require('mypkg');

Importing from ESM:

import {x} from 'mypkg/esm';

We did an investigation into ESM support in 05.2019 and found that a lot of libraries were lacking support (hence the recommendation for backward compatibility):

• esm package's support doesn't align with Node's which causes issues
  • "Builtin require cannot sideload .mjs files." https://github.com/standard-things/esm#loading, https://github.com/standard-things/esm/issues/498#issuecomment-403496745
  • "The .mjs file extension should not be the thing developers reach for if they want interop or ease of use. It's available since it's in --experimental-modules but since it's not fully baked I can't commit to any enhancements to it." https://github.com/standard-things/esm/issues/498#issuecomment-403655466
• mocha doesn't have native support for .mjs files
  • Update 2020-01-13: Mocha released experimental support in mocha@7.0.0-esm1
• Many high-profile projects had issues with .mjs files:
  • create-react-app
  • react-apollo
  • graphql-js
  • inferno