Worker
- Node.js course
- Advanced
- Lesson 8/83
- 5 min
Learn to create workers with new Worker.
new Worker
The new Worker(filename) call runs the given file in a new thread. filename is the path to a JavaScript file; it runs as a worker in a separate thread.
The Worker constructor also takes a { workerData } option to send initial data to the worker. On the worker side you access it via workerData. The main thread catches messages with worker.on("message") on the Worker object.
Worker events
A Worker object is an EventEmitter and emits three core events. "message" fires when the worker calls parentPort.postMessage. "error" fires on an uncaught error in the worker. "exit" fires when the worker thread closes.
You listen with worker.on("message", handler). Always listening for the error event is a good habit; otherwise a worker error can crash the parent.
Practice Log the type of Worker
Import the Worker class from worker_threads. Log typeof Worker.
Starter code
// Import the Worker class
// log its typeSample solution
const { Worker } = require("worker_threads");
console.log(typeof Worker);Expected output
function
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the class name
const worker = new ____("./worker.js")const worker = new Worker("./worker.js")Explanation: new Worker("./worker.js") starts the thread.
2 What is the first parameter of new Worker(...)?
- A number (port)
- Bir dize mesaj
- Bir fonksiyon
- Bir dosya yolu Correct answer
Explanation: The first parameter is the file path to run as a worker.
3 Match each piece to its role
| Term | Meaning |
|---|---|
new Worker("./w.js") |
Starts a worker |
worker.on("message") |
Waits for message |
worker.on("error") |
Catches error |
worker.on("exit") |
Catches exit |