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Node.js Basics

Run JavaScript on the server/CLI with Node.js. Access file system, processes, and network APIs.

Modules

Use ESM (recommended) with "type": "module" or .mjs; CJS remains common in legacy code.

// ESM
import { readFile } from 'node:fs/promises'
const text = await readFile('file.txt', 'utf8')

// CJS
const fs = require('fs')
const text2 = fs.readFileSync('file.txt', 'utf8')

fs and path

import { readFile, writeFile, mkdir } from 'node:fs/promises'
import { join } from 'node:path'
await mkdir('out', { recursive: true })
await writeFile(join('out', 'data.txt'), 'hello')

process

Environment, args, exit codes.

process.env.NODE_ENV
process.argv.slice(2)
process.exit(0)

CLI scripting

Use shebang and make executable.

#!/usr/bin/env node
console.log('Hello from Node')

HTTP (built-in)

import http from 'node:http'
http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' })
  res.end('ok')
}).listen(3000)

Prefer frameworks like Express/Fastify for apps.

Summary

  • Prefer ESM; use fs/path/process for I/O and env
  • Build CLIs with shebang and process.argv; use built‑in HTTP or frameworks
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