ES Modules (ECMAScript Modules) are JavaScript's native module system. They allow you to organize code into reusable pieces using import and export statements, making code more maintainable and enabling better dependency management.

How do I use ES Modules in the browser?

To use ES Modules in browsers, add type='module' to your script tag: <script type='module' src='app.js'></script> . Modern browsers support ES Modules natively, and module scripts are deferred by default.

What is the difference between ES Modules and CommonJS?

ES Modules use import/export syntax and are part of the JavaScript standard, while CommonJS uses require()/module.exports and was designed for Node.js. ES Modules are statically analyzed, support tree-shaking, and work in both browsers and Node.js.

Do I need a bundler to use ES Modules?

No, modern browsers support ES Modules natively. However, bundlers like Vite, Webpack, or Rollup are often used in production for optimization, compatibility with older browsers, and features like code splitting and minification.

How do I fix 'Cannot use import statement outside a module' error?

Add type='module' to your script tag in HTML, or set 'type': 'module' in your package.json for Node.js. This tells the JavaScript engine to treat your code as an ES Module.

Can I use ES Modules in Node.js?

Yes, Node.js has supported ES Modules since version 12. Use .mjs file extension or set 'type': 'module' in package.json. You can import built-in modules like import { readFile } from 'fs/promises'.

What is dynamic import in ES Modules?

Dynamic import() allows you to load modules on-demand at runtime. It returns a Promise and enables code splitting and lazy loading: const module = await import('./my-module.js').

Do ES Modules need file extensions?

Yes, in browsers file extensions are required: import { util } from './utils.js'. In Node.js, extensions are recommended for ES Modules. TypeScript files (.ts) are transpiled to .js during build.

Can I experiment with the live examples on ESModules.com?

Yes! Every live example includes a one-click 'Edit in CodePen' button. You can modify code, see results instantly, save your experiments, and share with others. All 8 examples work perfectly in CodePen with automatic module inlining for compatibility.

What topics does ESModules.com cover?

ESModules.com covers 31 in-depth pages spanning fundamentals, history and evolution, import attributes, import maps, module resolution, runtimes (Node.js, Deno, Bun), TypeScript integration, testing, frameworks (React, Vue, Svelte, Angular), WebAssembly, publishing packages, Web Workers, performance, debugging, security, migration, patterns, comparisons, tooling, real-world examples, and more.

Is ES Modules the standard for JavaScript in 2026?

Yes. ES Modules (ESM) is the universal standard for JavaScript modules in 2026. All major browsers, Node.js, Deno, and Bun support ESM natively. New features like import attributes and import maps have reached broad adoption, and the ecosystem has largely completed the migration from CommonJS to ESM.

ESModules.com - Master JavaScript ES Modules

Our Mission: Empowering Developers with the Future of JavaScript Modules

JavaScript has evolved. The days of global namespace pollution, complex bundler configurations, and competing module formats are giving way to a standardized, powerful, and native solution: ES Modules. This is the future of writing clean, reusable, and performant code for the web, and ESModules.com is your definitive resource for mastering it.

Our mission is to accelerate the awareness and adoption of this critical technology. We believe that a deep understanding of ES Modules is no longer optional - it's a foundational skill for modern developers committed to continuous learning and building for the long term.

Created By Developers, For Developers

This site isn't just a collection of documentation; it's a living project built from real-world experience. The team at RJL.dev - a group of practicing software engineers and architects - created and actively maintains every piece of content you'll find here. We've navigated the challenges, debugged the tricky edge cases, and optimized the patterns so you can learn from our expertise.

Because we are in the trenches coding every day, we stand behind our content with confidence. We are committed to providing you with:

In-Depth Tutorials

Clear, step-by-step guides that take you from foundational concepts to advanced techniques.

Actionable Best Practices

Go beyond the syntax to learn the patterns and strategies for writing truly maintainable and scalable modular code.

Practical Code Examples

Real-world, copy-paste-ready snippets that solve common problems and illustrate key principles.

Expert Debugging Techniques

Learn how to diagnose and fix module resolution errors, circular dependencies, and other common pitfalls.

Curated Resources

A handpicked collection of the best tools, articles, and documentation from around the web to supplement your learning.

ESModules.com is more than a website; it's our commitment to elevating the JavaScript community. We invite you to dive in, explore the resources, and join us in building the future of the web - one module at a time.

Frequently Asked Questions

Quick answers to common ES Modules questions

require() is a CommonJS function that's not available in ES Module scope. They're different module systems with different semantics:

❌ This won't work:

// In an ES Module file
const fs = require('fs'); // ReferenceError: require is not defined

✅ Use this instead:

// In an ES Module file
import fs from 'fs';

If you need to use CommonJS modules in an ESM context, you can still import them:

import cjsModule from 'some-commonjs-package';

Migration guide from CommonJS to ESM

CORS (Cross-Origin Resource Sharing) errors occur when loading modules from file:// protocol or different origins. Common solutions:

✅ Solution 1: Use a Local Server

Don't open HTML files directly. Use a development server:

# Using Node.js
npx http-server

# Using Python
python -m http.server 8000

# Using VS Code
# Install "Live Server" extension

✅ Solution 2: Use a Modern Dev Tool

Tools like Vite automatically handle CORS:

npm create vite@latest my-project
cd my-project
npm install
npm run dev

✅ Solution 3: Configure Server CORS Headers

If loading from a different domain, configure the server to allow cross-origin requests.

Master JavaScript ES Modules

What You'll Learn

Fundamentals

History & Evolution

In Practice

Runtimes

Advanced Topics

Comparisons

Import Attributes

Import Maps

Tooling & Ecosystem

TypeScript & ESM

Migration Guide

Module Resolution

Common Patterns

Testing with ESM

Performance

Debugging

Security

Frameworks & ESM

WebAssembly & ESM

Publishing Packages

Worker Modules

Real-World Examples

Resources & References

Cheat Sheet

📋 Copy-Paste Templates

Glossary

FAQ

Learn by Doing

6 Live Examples

Edit in CodePen

Real Execution

Our Mission: Empowering Developers with the Future of JavaScript Modules

Created By Developers, For Developers

In-Depth Tutorials

Actionable Best Practices

Practical Code Examples

Expert Debugging Techniques

Curated Resources

Frequently Asked Questions

What's the difference between ES Modules and CommonJS?

Do I need a bundler to use ES Modules?

Why can't I use require() with ES Modules?

Can I experiment with the live examples?

What you can do:

What's the difference between .js and .mjs file extensions?

How do I fix CORS errors with ES Modules?

Can I use ES Modules in older browsers?

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