HTML5 HTML5 Web Workers 3

Question 1

Which of the following correctly checks if Web Workers are supported in the current browser?

Accepted Answer

if (typeof Worker !== 'undefined') { ... }

Answer

if (window.supportsWorkers) { ... }

Answer

if (navigator.webWorkers === true) { ... }

Answer

if (document.hasWorkerSupport()) { ... }

Question 2

What happens to a Dedicated Web Worker when the web page that created it is closed?

Accepted Answer

The worker is automatically terminated by the browser

Answer

The worker continues running in the background indefinitely

Answer

The worker is moved to a shared worker pool

Answer

The worker saves its state to localStorage and resumes on next visit

Question 3

In a Service Worker, what lifecycle event fires after installation, when the worker takes control of clients?

Accepted Answer

activate

Answer

install

Answer

fetch

Answer

claim

Question 4

Which API do Service Workers use to cache network responses for offline use?

Accepted Answer

Cache API (caches.open())

Answer

localStorage API

Answer

IndexedDB API

Answer

sessionStorage API

Question 5

What is the scope of a Service Worker, and how is it determined?

Accepted Answer

The scope is the directory path of the service worker script file, controllable via the 'scope' option in registration

Answer

The scope is always the entire origin (domain) regardless of file location

Answer

The scope is set explicitly in the service worker script using self.setScope()

Answer

The scope is determined by the Content-Security-Policy header of the page

Question 6

Which postMessage() syntax correctly transfers (not copies) an ArrayBuffer to a Web Worker?

Accepted Answer

worker.postMessage(buffer, [buffer])

Answer

worker.postMessage(buffer, {transfer: true})

Answer

worker.postMessage({data: buffer, transferable: true})

Answer

worker.transfer(buffer)

Question 7

What is the correct way to register a Service Worker in a web application?

Accepted Answer

navigator.serviceWorker.register('/sw.js')

Answer

new ServiceWorker('/sw.js')

Answer

document.registerServiceWorker('/sw.js')

Answer

window.serviceWorker.install('/sw.js')