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Describe the Node.js module system. What are CommonJS and ES Modules?

Q: Describe the Node.js module system. What are CommonJS and ES Modules?

**TL;DR.** Node ships **two** module systems. **CommonJS (CJS)** uses require() / module.exports , loads **synchronously** at runtime, and is dynamic. **ES Modules (ESM)** use import / export , are **statically analyzed** before execution, support **top-level await** and tree-shaking, and are the JavaScript standard. Node decides per file via extension and the package "type" field. CommonJS require / module.exports synchronous, dynamic .cjs or "type":"commonjs" <text class='d-sub'

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This question covers a foundational aspect of Node.js application structure and dependency management.

modulescommonjses modulesdependencies

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Same module, both systems

// CommonJS
const fs = require('node:fs');
module.exports = { ready: true };

// ES Module
import fs from 'node:fs';
export const ready = true;
const mod = await import('./dynamic.js');  // dynamic import works in both

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