HTML5 HTML5 Web Workers

Question 1

What is the primary purpose of HTML5 Web Workers?

Accepted Answer

To run JavaScript in a background thread without blocking the main UI thread

Answer

Web Workers allow scripts to run in background threads, keeping the main thread free and preventing UI freezing during heavy computations.

Question 2

Which of the following correctly creates a new Web Worker?

Accepted Answer

var worker = new Worker('worker.js');

Answer

The Worker constructor takes the URL of a script file as its argument to instantiate a new background worker.

Question 3

How does the main thread send a message to a Web Worker?

Accepted Answer

worker.postMessage(data)

Answer

The postMessage() method is used on both sides of the worker communication channel to pass data.

Question 4

Inside a Web Worker, which global object is available instead of 'window'?

Accepted Answer

self

Answer

Inside a Web Worker, 'self' refers to the worker's global scope (DedicatedWorkerGlobalScope), since 'window' is not available.

Question 5

Which of the following resources is NOT accessible inside a Web Worker?

Accepted Answer

The DOM (document object)

Answer

Web Workers run in a separate thread and do not have access to the DOM, window, or document objects for thread-safety reasons.

HTML5 - HTML5 Web Development Practice Test