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🟢 Node.js — Node.js — fs, http, path, process, npm modules

Node.js runs JavaScript on the server using Chrome's V8 engine. It provides built-in modules for file system, HTTP, networking, and process management. Non-blocking I/O makes it ideal for API servers and real-time applications.

📋 Methods & APIs

Name	Signature / Syntax	Description
require	const fs = require('fs')	Import CommonJS module (legacy Node)
import	import fs from 'fs/promises'	Import ES module (add type:module to package.json)
fs.readFile	fs.readFile(path, 'utf8', callback)	Read file asynchronously (callback)
fs.readFileSync	fs.readFileSync(path, 'utf8') → string	Read file synchronously
fs.writeFile	fs.writeFile(path, data, callback)	Write file asynchronously
fs.promises.readFile	await fs.promises.readFile(path, 'utf8')	Read file with async/await
fs.promises.writeFile	await fs.promises.writeFile(path, data)	Write file with async/await
fs.promises.readdir	await fs.promises.readdir(dir)	List directory contents
fs.promises.mkdir	await fs.promises.mkdir(dir, {recursive:true})	Create directory
fs.promises.stat	await fs.promises.stat(path)	Get file metadata
path.join	path.join(dir, 'sub', 'file.txt')	Join path components (OS-aware)
path.resolve	path.resolve('./relative')	Resolve to absolute path
path.dirname	path.dirname('/foo/bar.txt') → '/foo'	Directory part of path
path.basename	path.basename('/foo/bar.txt') → 'bar.txt'	Filename part of path
path.extname	path.extname('file.js') → '.js'	Extension part of path
http.createServer	http.createServer((req,res) => {})	Create HTTP server
req.url / req.method	req.url → string / req.method → string	Request URL and HTTP method
res.writeHead	res.writeHead(200, {'Content-Type':'text/html'})	Set status and headers
res.end	res.end(body)	Send response and close connection
process.env	process.env.PORT \|\| 3000	Access environment variables
process.argv	process.argv[2]	Command-line arguments
process.cwd	process.cwd() → string	Current working directory
process.exit	process.exit(0)	Exit Node process
console.log/error	console.log() / console.error()	Log to stdout / stderr
__dirname	__dirname	Directory of current module (CommonJS)
__filename	__filename	Path of current module (CommonJS)
Buffer	Buffer.from('hello') / Buffer.alloc(n)	Work with binary data
EventEmitter	const ee = new EventEmitter()	Publish-subscribe pattern
stream.Readable	new Readable({ read() {} })	Create readable stream
stream.pipeline	pipeline(readable, writable, cb)	Safely pipe streams

💡 Example

Run with node script.js or save as HTML and open in browser.

// Node.js HTTP Server + File System
// Save as server.js and run: node server.js
const http  = require('http');
const fs    = require('fs').promises;
const path  = require('path');
const url   = require('url');

const PORT = process.env.PORT || 8080;
const DATA_FILE = path.join(__dirname, 'data.json');

// Initialize data file
async function initData() {
  try { await fs.access(DATA_FILE); }
  catch { await fs.writeFile(DATA_FILE, JSON.stringify({ students: [] })); }
}

// Simple router
const routes = {
  'GET /': async (req, res) => {
    res.writeHead(200, { 'Content-Type': 'text/html' });
    res.end(`
      <h1>MyWebUniversity API</h1>
      <ul>
        <li>GET  /students</li>
        <li>POST /students  (JSON body)</li>
        <li>GET  /health</li>
      </ul>`);
  },
  'GET /health': async (req, res) => {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ status: 'ok', uptime: process.uptime().toFixed(1) }));
  },
  'GET /students': async (req, res) => {
    const raw  = await fs.readFile(DATA_FILE, 'utf8');
    const data = JSON.parse(raw);
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify(data.students));
  },
  'POST /students': async (req, res) => {
    let body = '';
    for await (const chunk of req) body += chunk;
    const student = JSON.parse(body);
    const raw  = await fs.readFile(DATA_FILE, 'utf8');
    const data = JSON.parse(raw);
    data.students.push({ id: Date.now(), ...student });
    await fs.writeFile(DATA_FILE, JSON.stringify(data, null, 2));
    res.writeHead(201, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ ok: true, count: data.students.length }));
  },
};

const server = http.createServer(async (req, res) => {
  const { pathname } = url.parse(req.url);
  const key = `\${req.method} \${pathname}`;
  const handler = routes[key];
  if (handler) {
    try { await handler(req, res); }
    catch (e) {
      res.writeHead(500, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify({ error: e.message }));
    }
  } else {
    res.writeHead(404); res.end(JSON.stringify({ error: 'Not found' }));
  }
});

initData().then(() => {
  server.listen(PORT, () => console.log(`Server running on http://localhost:\${PORT}`));
});
// node server.js
// curl http://localhost:8080/health
// curl -X POST http://localhost:8080/students -H 'Content-Type:application/json' -d '{"name":"Alice","score":95}'

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