Cross-Browser Compatibility & Testing — Test 1

Correct Answer: D. caniuse.com
Explanation: MDN's compatibility tables give the same kind of information.

Correct Answer: C. Code that implements a missing modern feature in older browsers
Explanation: A transpiler (such as Babel) converts new syntax. A polyfill adds missing APIs. They are complementary. ALSO KNOW (related points): • Which website is commonly used to check which browsers support a given HTML, CSS, or JavaScript feature? → caniuse.com • Which tool automates real browsers (Chrome, Firefox, Edge, Safari) through browser-specific drivers such as chromedriver and geckodriver? → Selenium WebDriver • What does a web page that works in Chrome but breaks in Safari most likely indicate? → The page uses a feature or behavior that WebKit does not support, or supports differently • Which plugin technology reached end of life in all major browsers in 2020–2021? → Adobe Flash Player • What is WebAssembly (Wasm)? → A binary instruction format that runs at near-native speed in all major browsers • Which shortcut zooms the page back to 100% in most browsers? → Ctrl + 0

Correct Answer: C. Feature detection (checking whether an API exists) rather than User-Agent sniffing
Explanation: For example, check if ('geolocation' in navigator) before using geolocation. ALSO KNOW (related points): • What were vendor prefixes such as -webkit-, -moz-, and -ms- used for in CSS? → Experimental or non-standard implementations of CSS features in specific engines • What is a headless browser? → A browser that runs without a visible user interface, used for automated testing and scraping • What is a favicon? → The small site icon shown in browser tabs, bookmarks, and history • Which statement about browser sync, such as signing into Chrome or Firefox, is correct? → It synchronizes bookmarks, passwords, history, and settings across devices using your account

Correct Answer: B. Experimental or non-standard implementations of CSS features in specific engines
Explanation: Browsers now prefer feature flags over prefixes. Autoprefixer adds prefixes automatically.

Correct Answer: B. Selenium WebDriver
Explanation: Playwright supports the Chromium, Firefox, and WebKit engines with a single API.

Correct Answer: D. A browser that runs without a visible user interface, used for automated testing and scraping
Explanation: For example, Chrome can run with the --headless flag, and Puppeteer controls headless Chrome.

Correct Answer: D. The page uses a feature or behavior that WebKit does not support, or supports differently
Explanation: Test early in all target engines, not only in Chromium.

Correct Answer: C. Adobe Flash Player
Explanation: HTML5 video, canvas, and WebAssembly replaced Flash.

Correct Answer: D. A binary instruction format that runs at near-native speed in all major browsers
Explanation: Code written in languages such as C++, Rust, and C# can be compiled to Wasm.

Correct Answer: D. They can intercept and modify network requests, so they need a secure origin to prevent tampering
Explanation: Service workers are the basis of Progressive Web Apps (offline support and push notifications). ALSO KNOW (related points): • In Chrome, what is the address bar called that combines URL entry with search? → Omnibox • Which statement about bookmarklets is correct? → They are bookmarks whose URL begins with javascript:, which run code on the current page • What does about:blank do? → It opens an empty page generated internally by the browser, without contacting any server