What are Worker Threads in Node.js? | Node.js Interview Questions

What You'll Learn

What worker threads are
When to use them
How to implement

What are Worker Threads?

Worker Threads allow running JavaScript in parallel threads, useful for CPU-intensive tasks without blocking the main thread.

Worker Threads vs Cluster

Feature	Worker Threads	Cluster
Memory	Shared (SharedArrayBuffer)	Separate
Use case	CPU-intensive tasks	Scaling HTTP servers
Communication	postMessage, shared memory	IPC

Basic Example

code.jsJavaScript

// main.js
const { Worker } = require('worker_threads');

const worker = new Worker('./worker.js', {
  workerData: { num: 42 }
});

worker.on('message', (result) => {
  console.log('Result:', result);
});

worker.on('error', (err) => {
  console.error('Worker error:', err);
});

worker.on('exit', (code) => {
  console.log('Worker exited with code:', code);
});

code.jsJavaScript

// worker.js
const { parentPort, workerData } = require('worker_threads');

// CPU-intensive calculation
function fibonacci(n) {
  if (n <= 1) return n;
  return fibonacci(n - 1) + fibonacci(n - 2);
}

const result = fibonacci(workerData.num);
parentPort.postMessage(result);

Shared Memory

code.jsJavaScript

// main.js
const { Worker } = require('worker_threads');

const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);

const worker = new Worker('./worker.js', {
  workerData: { sharedBuffer }
});

// worker.js
const { workerData } = require('worker_threads');
const sharedArray = new Int32Array(workerData.sharedBuffer);
Atomics.add(sharedArray, 0, 1);