Web Development Performance Optimization 5

Question 1

What does the 'stale-while-revalidate' caching strategy do?

Accepted Answer

Serves a cached response immediately while fetching an updated version in the background

Answer

Stale-while-revalidate returns the cached response instantly and asynchronously refreshes it so the next request gets a fresh version.

Question 2

Which Core Web Vital metric specifically measures visual stability by quantifying unexpected layout shifts?

Accepted Answer

Cumulative Layout Shift (CLS)

Answer

CLS measures the sum of all unexpected layout shift scores during a page's lifespan, quantifying visual instability.

Question 3

What is the primary purpose of gzip or Brotli compression on HTTP responses?

Accepted Answer

To reduce the transfer size of text-based assets like HTML, CSS, and JS

Answer

Gzip and Brotli compress text responses before sending, reducing bytes transferred over the network and improving load times.

Question 4

Which approach should you use to avoid long tasks blocking the main thread in JavaScript?

Accepted Answer

Breaking long tasks into smaller chunks using setTimeout or scheduler.yield()

Answer

Yielding to the browser between chunks (via setTimeout(0) or scheduler.yield()) lets the browser handle user input between work units.

Question 5

What is the benefit of specifying explicit width and height attributes on <img> elements?

Accepted Answer

It allows the browser to reserve space before the image loads, preventing layout shifts

Answer

Explicit dimensions let the browser calculate the aspect ratio and reserve the correct space, eliminating layout shifts as images load.

Web Development Practice Test