worker_threads

Learn CPU-heavy tasks with worker_threads.

What is worker_threads?

The Node.js event loop is single-threaded; heavy CPU work can block the whole process. The worker_threads module lets you create true parallel threads. Unlike cluster, workers are not separate processes but parallel threads inside the same process, and they can share memory.

The module is built in: you import it with require("worker_threads"). It is ideal for CPU-heavy work (image processing, cryptography, big calculations). For I/O work the event loop is already enough.

isMainThread and parentPort

The worker_threads module exposes two key properties. isMainThread returns true in the main thread and false in a worker. parentPort gives the worker a port to message the parent; it is null in the main thread.

A typical pattern: the main thread starts a worker with new Worker(...); the worker sends results back with parentPort.postMessage(...). This mirrors cluster's IPC model but runs inside a single process.

Exercise Log the isMainThread value

Import isMainThread from worker_threads. Log its value with console.log.

Show example solution

const { isMainThread } = require("worker_threads");
console.log(isMainThread);

Test yourself

What is worker_threads used for?
- Speeding up network requests
- Shortening file writes
- Running CPU-heavy work in parallel
- Rendering an HTML page
Show answer

Running CPU-heavy work in parallel — worker_threads is used to parallelize CPU-heavy work.

Complete the module name

const { Worker } = require("____")

Show answer

const { Worker } = require("worker_threads")

Match each piece to its role

worker_threads

Parallel threads
isMainThread

Main thread?
parentPort

Parent link
Worker

Worker class

Next lesson: Worker

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