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Explain how modules work in Node.js.

Q: Explain how modules work in Node.js.

**TL;DR.** A **module** is a file with its **own scope**: variables are private unless explicitly exported. Node supports two systems — **CommonJS** ( require / module.exports , loaded synchronously) and **ES Modules** ( import / export , statically analyzed). Each file is loaded once and **cached**, so repeated requires return the same instance. math.js const PI = 3.14 (private) exports: add, sub <tex

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Tests understanding of Node.js's modular system.

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Export, import, and caching

// math.js (CommonJS)
const PI = 3.14159;                  // private to the module
function add(a, b) { return a + b; }
module.exports = { add };            // public surface

// app.js
const m1 = require('./math');
const m2 = require('./math');
console.log(m1 === m2);              // true — cached singleton

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