The Evolution of JavaScript Modules: A New Era for Node.js

A Brief History of ES Module Support

June 2015 marked a significant milestone with the definition of ES modules in the ES2015 specification. Initially, major browsers added experimental support behind developer flags, and Node.js followed suit with v8.5 in September 2017. By May 2018, browsers began supporting ES modules without flags, paving the way for widespread adoption.

Why ES Module Support Matters for Node.js

With all major browsers already supporting ES modules, it’s essential for Node.js to follow suit. This will enable full-stack developers to write modular, reusable JavaScript for both client and server sides. Moreover, experimental features in Node.js are subject to changes or removal, making it crucial to establish a stable and standardized module system.

Understanding CommonJS and ES Modules

CommonJS modules, currently the de facto standard in Node.js, are defined in normal.js files using module.exports. In contrast, ES modules, introduced in Node v8.5, use the --experimental-modules flag and are defined in.mjs files (or.js files under certain circumstances).

// CommonJS example
module.exports = {
  foo: 'bar'
};

// ES Module example
export const foo = 'bar';

Using CommonJS and ES Modules Together

Developers can work with both types of modules simultaneously, even importing from one to the other. This interoperability ensures a seamless transition to a future without CommonJS.

// Importing a CommonJS module in an ES Module
import cjsModule from './cjs-module.js';
console.log(cjsModule.foo); // outputs "bar"

// Importing an ES Module in a CommonJS module
const esModule = require('./es-module.mjs');
console.log(esModule.foo); // outputs "bar"

The Future of Modular JavaScript

As Node.js moves towards full support for ES modules, several key features are being developed, including:

• Loaders
• Code coverage
• Pluggable loaders
• Runtime loaders
• The “exports” object in package.json, allowing packages to provide “pretty” entry points for different components

Dual ESM/CommonJS Packages and the Path Forward

To ensure a backwards-compatible, developer-friendly path to migrate from CommonJS to ES modules, dual-mode support is essential. This will enable npm packages to contain both CJS and ES modules, making it easier for developers to ship packages with two separate implementations.

ES Modules vs. CommonJS: The Future Ahead

While ES modules are poised to eventually replace CommonJS modules in Node.js, the exact timeline remains unclear. One thing is certain, however: Node developers have worked tirelessly to ensure a seamless transition, striking a balance between interoperability and avoiding unnecessary dual-mode APIs.