The Event Loop is the mechanism that allows Node.js to perform non-blocking I/O operations despite being single-threaded. It continuously checks the call stack and processes callbacks from the event queue.
Node's built-in http module lets you create a web server in just a few lines of code.
// Event Loop phases (simplified):
// 1. timers — setTimeout / setInterval callbacks
// 2. I/O — completed I/O callbacks
// 3. poll — retrieve new I/O events
// 4. check — setImmediate callbacks
// 5. close — close event callbacks
// ---- Your first HTTP server ----
const http = require('http');
const server = http.createServer((req, res) => {
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('Hello, World!\n');
});
const PORT = 3000;
server.listen(PORT, () => {
console.log(`Server running at http://localhost:${PORT}/`);
});
// Visit http://localhost:3000 in your browser.
// Node.js handles each request asynchronously,
// so the server keeps listening for more requests.