CommonJS vs. ESM/ECMAScript cheat-sheet

Short comparison of the most common statements in CommonJS vs. ESM/ECMAScript for importing, exporting and in your package.json.

See the table below for a brief comparison on the most used statements that should cover the vast majority of use-cases.

Use-CaseCommonJSESM / ECMAScript
Default import
(NPM module)
const imp = require('module');import imp from 'module';
Default import
(own module)
const imp = require('./myModule');

Note: path is mandatory, file extension is optional
import imp from './myModule.js';

Note: path and file extension are mandatory
Named importconst { namedImp } = require('module');import { namedImp } from 'module';
Import with function
const funcImp = require('module')(myParam);import imp from 'module';
const funcImp = imp(myParam);

Note: ESM doesn’t support invocations
on importing, so two lines of code are needed
Default export
module.exports = function() {/* */}export default function() {/* */}
Named export
(e.g. a function, works also with objects, classes etc.)
module.exports.myFunction = function() {/* */}export function myFunction() {/* */}
Exporting an arrow functionmodule.exports.myFunction = () => {/* */}export const MyFunction = () => {/* */}

Note: the const keyword is needed here
package.json entries
Module type…nothing…
"type": "commonjs"

Note: since CommonJS is the default, normally no type entry is present in package.json
"type": "module"

Note: this tells Node.js to treat all .js files as ES modules without the need to use the .mjs extension which is often preferred
Entry point"main": "index.js""exports": "./index.js"

Note: path and file extension are mandatory

Please note that this cheat-sheet is just an excerpt of all possible module.exports/require and import/export constellations as well as all available package.json options. For more details, refer to the very comprehensive documentation sites:

If you are about to migrate from CommonJS, also check out the article on converting an existing Node.js project to ESM.

Happy coding 😉