CommonJS vs ES Modules in Node.js: Which Should You Use?

CommonJS vs ES Modules in Node.js: Which Should You Use?

Node.js supports two module systems: CommonJS and ES modules. Here is how they compare and which to choose.

CommonJS

Uses require and module.exports. Synchronous, runtime-loaded, and traditional in Node.js. Most existing Node.js code uses CommonJS.

ES Modules

Uses import and export. Asynchronous, statically analyzable, and the modern JavaScript standard. Supported in Node.js via 'type': 'module' in package.json or .mjs file extensions.

Key Differences

CommonJS is synchronous and loaded at runtime; ES modules are async and statically analyzable. CommonJS allows conditional require; ES module imports must be at the top level. CommonJS uses module.exports; ES modules use export.

When to Use CommonJS

For existing projects that already use it, for libraries that document CommonJS usage, and for maximum ecosystem compatibility, since most npm packages were built for CommonJS.

When to Use ES Modules

For new projects that want the modern standard, for static analysis benefits like tree-shaking, and for consistency with frontend code that uses ES modules.

Mixing Them

Node.js supports interoperability, but mixing is complex. For a clean setup, pick one system per project. If you must mix, use dynamic import() to load ES modules from CommonJS.

The Takeaway

Use CommonJS for existing projects and maximum ecosystem compatibility. Use ES modules for new projects wanting the modern standard and static analysis. Pick one per project; mixing is complex and best avoided.