Node.js: Server-Side JavaScript

Node.js Fundamentals

Node.js runs JavaScript outside the browser. Built on V8 with an event-driven, non-blocking I/O model — excellent for scalable network applications and CLI tools.

// Node.js globals:
console.log(__dirname);    // current directory
console.log(__filename);   // current file path
console.log(process.env.NODE_ENV);  // environment
console.log(process.argv); // CLI arguments

// Built-in modules:
const os = require("os");
const path = require("path");
const http = require("http");

console.log(process.version);    // Node version
console.log(os.platform());      // "linux"/"win32"/"darwin"
console.log(os.cpus().length);   // CPU count
console.log(os.freemem() / 1e9 + " GB free");

// Simple HTTP server:
const server = http.createServer((req, res) => {
  if (req.url === "/") {
    res.writeHead(200, { "Content-Type": "text/html" });
    res.end("<h1>Hello from Node.js!</h1>");
  } else if (req.url === "/api") {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(JSON.stringify({ ok: true, timestamp: Date.now() }));
  } else {
    res.writeHead(404);
    res.end("Not Found");
  }
});

server.listen(3000, () => console.log("Server on :3000"));