CommonJS vs ESM

Learn the difference between CommonJS (require) and ES modules.

CommonJS vs ESM

Node.js has two module systems: CommonJS (old) and ES modules (modern). ESM is recommended in Node.js 22.

In CommonJS, you export with module.exports and import with require. In ESM, you use export and import.

Mixing the two in one project causes errors; you select ESM by setting "type": "module" in package.json. You may see CommonJS in old code, but use ESM in new code.

Which should you choose?

When starting a new project, choosing ESM is recommended. If you add "type": "module" to package.json, all your .js files are treated as ESM.

If you are maintaining an old project that uses require, staying with CommonJS may be the consistent choice. Still, prefer ESM for new additions.

Do not mix the two systems in the same file; it is confusing and leads to errors.

Exercise Write an ESM import

Import the greet function from ./hello.js. Then call console.log with greet('World').

Show example solution

import { greet } from "./hello.js";

console.log(greet("World"));

Test yourself

Import with require

CommonJS: const fs = ____("fs");

Show answer

CommonJS: const fs = require("fs");

What does "type": "module" do?
- Deletes all .js files
- Recognizes only .mjs files
- Disables npm commands
- Treats all .js files as ESM
Show answer

Treats all .js files as ESM — type: module treats .js files as ESM.
Match the module systems

require

CommonJS import
import

ESM import
module.exports

CommonJS export
export

ESM export

Next lesson: Summary - Node.js basics

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