Offload CPU-Intensive Tasks with Node.js worker_threads

Problem

Running CPU-intensive operations like image processing or large JSON parsing in Node.js blocks the event loop. Your API stops responding, and all other requests queue up.

Solution

Use the built-in worker_threads module to offload heavy computation to a separate thread.

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

function heavyCalculation(data) {
  let result = 0;
  for (let i = 0; i < data.iterations; i++) {
    result += Math.sqrt(i) * Math.random();
  }
  return result;
}

const result = heavyCalculation(workerData);
parentPort.postMessage(result);

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

function runWorker(data) {
  return new Promise((resolve, reject) => {
    const worker = new Worker('./worker.js', { workerData: data });
    worker.on('message', resolve);
    worker.on('error', reject);
  });
}

app.get('/heavy', async (req, res) => {
  const result = await runWorker({ iterations: 10_000_000 });
  res.json({ result });
  // Other requests continue to be served normally
});

For repeated tasks, use a worker pool to avoid creation overhead:

const os = require('os');
const poolSize = os.cpus().length;
const workers = Array.from({ length: poolSize },
  () => new Worker('./worker.js')
);

Key Points

• worker_threads is built into Node.js — no external dependencies needed
• Pass data via workerData, return results via parentPort.postMessage()
• The main event loop stays unblocked, keeping API responsiveness intact
• Use worker pools for repeated tasks to reduce thread creation overhead