Great question! Node.js is indeed single-threaded in terms of its main event loop, but it’s designed to handle concurrency in a clever and efficient way. Here's how it pulls that off:

Event Loop & Non-Blocking I/O

• Event-driven architecture: Node.js uses an event loop to manage asynchronous operations. Instead of waiting for tasks like file reads or network requests to complete, it registers callbacks and moves on.
• Non-blocking I/O: Most of Node’s core APIs (like fs, http, etc.) are non-blocking, meaning they delegate work to the system and continue executing other code.

Worker Threads & libuv

• libuv under the hood: Node.js uses the libuv library to handle asynchronous operations. It has a thread pool (usually 4 threads by default) for tasks that are too heavy for the event loop, like file system operations or DNS lookups.
• Worker Threads module: For true parallelism, Node.js introduced the worker_threads module. You can spawn separate threads to handle CPU-intensive tasks without blocking the main thread.

const { Worker } = require('worker_threads');

new Worker('./heavyTask.js'); // Runs in a separate thread

Clustering for Scaling

• Cluster module: If you want to take advantage of multi-core systems, you can use the cluster module to spawn multiple Node.js processes that share the same server port.

const cluster = require('cluster');

const os = require('os');

if (cluster.isMaster) {

  os.cpus().forEach(() => cluster.fork());

} else {

  require('./server'); // Each worker runs the server

}

Async/Await & Promises

• Modern syntax: With async/await, writing asynchronous code feels synchronous, making it easier to manage complex flows without blocking the thread.

async function fetchData() {

  const data = await fetch('https://api.example.com');

  return data.json();

}