ES modules (ESM)

ESM is the modern standard: import and export with static analysis-friendly syntax. New Node projects set "type": "module" in package.json; this playground runs as ESM (.mjs).

Named and default exports

// math.mjs
export function add(a, b) { return a + b; }
export default function multiply(a, b) { return a * b; }

// app.mjs
import multiply, { add } from './math.mjs';

Built-in imports

import fs from 'node:fs/promises';
import { readFile } from 'node:fs/promises';
import path from 'node:path';

The node: prefix clarifies built-ins and avoids npm name collisions.

Dynamic import

const mod = await import('./feature.mjs');

Loads conditionally—useful for lazy loading or optional dependencies.

Important interview questions and answers

1. Q: .mjs vs .js with "type":"module"?
   A: Both run as ESM; .mjs forces ESM even without package.json type; .cjs forces CommonJS.
2. Q: Can you require an ESM module?
   A: Not with sync require—use dynamic import() from CommonJS instead.

Self-check

1. What does the node: prefix indicate?
2. When use dynamic import()?

Tip: Use node: prefix for built-ins (import fs from 'node:fs/promises')—clearer and avoids shadowing npm packages named fs.