What are JavaScript modules?

Modules allow you to split code into separate files and import/export functionality.

ES6 Modules (ESM):

Exporting:

// math.js
export const PI = 3.14159;
export function add(a, b) {
  return a + b;
}
// Default export
export default function multiply(a, b) {
  return a * b;
}

Importing:

// main.js
import multiply, { PI, add } from "./math.js";
import * as math from "./math.js";
console.log(PI); // 3.14159
console.log(add(2, 3)); // 5
console.log(multiply(4, 5)); // 20

CommonJS (Node.js):

// Exporting
module.exports = { add, PI };
// Importing
const { add, PI } = require("./math");

Benefits:
- Code organization
- Reusability
- Namespace management
- Dependency management
- Tree shaking (dead code elimination)