Web Programming Web Performance and Optimization 3

Question 1

What is the Time to First Byte (TTFB) metric?

Accepted Answer

The time from when a request is sent until the browser receives the first byte of the response

Answer

TTFB measures the duration from the user's browser requesting a page to when the browser receives the first byte of data from the server, indicating server response performance.

Question 2

What is the purpose of preloading resources in web performance?

Accepted Answer

To tell the browser to fetch critical resources earlier in the page load lifecycle

Answer

Preloading instructs the browser to fetch important resources (fonts, critical CSS, key images) as early as possible in the page load to avoid delays when they're later needed.

Question 3

What does the Cumulative Layout Shift (CLS) Core Web Vital measure?

Accepted Answer

The visual stability of a page — how much unexpected content shifting occurs during load

Answer

CLS (Cumulative Layout Shift) measures the visual stability of a page by scoring unexpected shifts in layout that occur as content loads, affecting user experience.

Question 4

What is tree shaking in JavaScript bundling?

Accepted Answer

Eliminating dead code (unused exports) from the final JavaScript bundle

Answer

Tree shaking is a dead code elimination technique used by bundlers like Webpack and Rollup that removes JavaScript code that is exported but never imported or used.

Question 5

What is the difference between synchronous and asynchronous JavaScript loading?

Accepted Answer

Synchronous loading blocks HTML parsing; asynchronous loading allows HTML to continue parsing while JS downloads

Answer

Synchronous (default) script loading blocks HTML parsing until the script is fully downloaded and executed, while async/defer attributes allow the HTML to continue parsing concurrently.

Web Programming Practice Test

Web Programming Practice Test

Web Programming Web Performance and Optimization 3