About ES Modules in Node.js

What are ES Modules in Node.js?

In Node.js, the term "ES Modules" refers to a standardized way of organizing and managing JavaScript code using the import and export statements introduced in ECMAScript 2015 (also known as ES6).

ES Modules allow developers to split their code into smaller, more reusable pieces, and then import and use those pieces in other parts of their application. They can be used to import functions, objects, and other values from external modules, as well as to export values from the current module to be used by other modules.

From the official Node.js documentation, ES Modules are:

ECMAScript modules are the official standard format to package JavaScript code for reuse. Modules are defined using a variety of import and export statements.

Node.js has two module systems:

CommonJS modules - CJS
ECMAScript modules - ESM

CommonJS modules are simply not ES Modules! It imports and exports JavaScript code using the require() and module.exports statements.

From Node.js V14.0.0, ES Modules are stable. However, they do not default modules in Node.js. The default modules are still CommonJS modules. So, How can we use ES Modules in Node.js?

`How` can we use ES Modules in Node.js?

We can tell Node.js to use the ECMAScript modules loader via:

Rename .js file extension to .mjs file extension.
Set the package.json "type" field to "module" - "type": "module"
Set the --input-type=module flag when running Node CLI

Basic example

ES module exports a function:

// addTwo.mjs
const addTwo = (num) => {
  return num + 2;
}

export { addTwo };

// app.mjs
import { addTwo } from './addTwo.mjs';

// Prints: 6
console.log(addTwo(4));

'./addTwo.mjs' is actually exporting an object that contains a property named addTwo. When importing this module, we are using destructuring assignment feture to access the addTwo property.

Why we are moving to ES Modules?

This blog post explains the benefits of ES Modules clearly!

Compatibility with new packages
More readable code and better performance
TypeScript also uses ESM syntax by default

If you are using an older version of Node.js or a runtime that does not support ESM, you may not be able to use ESM packages directly. However, many ESM packages provide a CommonJS version of their package that can be used with the require() function and the module.exports object, which is supported by most JavaScript runtimes.

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