ESLint rules for migrating projects from CommonJS to ESM

migratingRules.md

ESLint rules

The ESM standard is considered stable in NodeJS and well supported by a lot of modern JavaScript tools.

ESLint does a good job validating and fixing ESM code (as long as you don't use top-level await, coming in ESLint v8). Make sure to enable the latest ECMA features in the ESLint config.

• .eslint.json

{
  "env": {
    "es2021": true,
    "node": true
  },
  "parserOptions": {
    "sourceType": "module"
  }
}

---

Rules that can be helpful for anyone who wants to migrate a project from CommonJS to ESM now:

eslint-plugin-node

ESLint Plugin	Rule	Source	Description	Fixable
node	no-missing-import	🔗	disallow import declarations which import non-existence modules	-
node	no-extraneous-import	🔗	disallow import declarations which import extraneous modules	-
node	no-sync	🔗	disallow synchronous methods	-
node	file-extension-in-import	🔗	enforce the style of file extensions in import declarations	Yes

eslint-plugin-import

ESLint Plugin	Rule	Source	Description	Fixable
import	extensions	🔗	Ensure consistent use of file extension within the import path.	-
import	no-unresolved	🔗	Ensure imports point to a file/module that can be resolved.	-
import	no-useless-path-segments	🔗	Prevent unnecessary path segments in import and require statements.	Yes
import	no-extraneous-dependencies	🔗	Forbid the use of extraneous packages.	-
import	no-commonjs	🔗	Report CommonJS require calls and module.exports or exports.*.	-

eslint-plugin-unicorn

ESLint Plugin	Rule	Source	Description	Fixable
unicorn	prefer-module	🔗	Prefer JavaScript modules (ESM) over CommonJS.	Yes
unicorn	prefer-node-protocol	🔗	Prefer using the node: protocol when importing Node.js builtin modules.	Yes
unicorn	prefer-top-level-await	🔗	Prefer top-level await over top-level promises and async function calls.	Suggest

Read more

• sindresorhus - Pure ESM package
• sindresorhus - Get Ready For ESM
• Node documentation - ECMAScript modules

Thank you very much for this very useful info! 👍

It is very helpful 👍

I've created a wrapper CLI of ESLint + rules.
This tool has built-in rules which are based on this article.

npx eslint-cjs-to-esm "./src/**/*.{js,ts}" --fix

• eslint-cjs-to-esm