Passing data to workers in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main way to send data to a worker thread in Node.js?

You send data to a worker thread by passing it as an argument when creating the Worker or by using the postMessage() method to send messages after the worker starts.

beginner

How does the worker thread receive data sent from the main thread?

The worker thread listens for messages using the parentPort.on('message', callback) event handler to receive data sent from the main thread.

intermediate

Can you pass complex objects like functions or class instances directly to a worker thread?

No, you cannot pass functions or class instances directly. Only data that can be serialized (like objects, arrays, strings, numbers) can be passed between threads.

beginner

What is the benefit of using workerData when creating a new Worker?

workerData allows you to send initial data to the worker thread at creation time, so the worker can start working immediately with that data.

beginner

How do you send data back from a worker thread to the main thread?

The worker thread uses parentPort.postMessage() to send data back to the main thread, which listens with worker.on('message').

Which method sends data from the main thread to a worker after it has started?

A emitMessage()

B workerData

C sendData()

D postMessage()

The postMessage() method sends data to a worker after it has started. workerData is only for initial data.

Where does a worker thread listen for incoming messages from the main thread?

A parentPort.on('message')

B worker.on('message')

C process.on('message')

D mainThread.on('message')

The worker thread listens on parentPort.on('message') to receive messages from the main thread.

What kind of data can be passed between the main thread and worker threads?

A Open file handles

B Functions and class instances

C Only serializable data like objects, arrays, strings, and numbers

D DOM elements

Only serializable data such as objects, arrays, strings, and numbers can be passed between threads.

How do you pass initial data to a worker thread when creating it?

A Using the workerData option in the Worker constructor

B Using postMessage() immediately after creation

C Using environment variables

D Using a global variable

Initial data is passed to a worker thread via the workerData option in the Worker constructor.

How does the main thread receive data sent from a worker thread?

A parentPort.on('message')

B worker.on('message')

C worker.postMessage()

D process.on('message')

The main thread listens for messages from a worker using worker.on('message').

Explain how data is passed from the main thread to a worker thread and how the worker receives it.

Think about the two ways to send data: at creation and after creation.

Describe the limitations on the types of data you can pass between the main thread and worker threads in Node.js.

Consider what can be converted to a message safely.