HTML Interview Questions and Answers

What is semantic HTML and why does it matter?

Semantic elements (header, nav, main, article, footer) describe meaning, not just appearance. It matters for accessibility (screen readers navigate by landmarks), SEO, and maintainability.

What's the difference between async and defer on a script?

Both download in parallel without blocking parsing. async runs as soon as it's ready (order not guaranteed) — good for analytics. defer runs after parsing, in order — best for app scripts that touch the DOM.

What is the DOM?

The Document Object Model — a tree of node objects the browser builds from your HTML. JavaScript reads and mutates the DOM to change the page after load.

What are ARIA roles and when do you use them?

ARIA attributes describe custom widgets to assistive tech when no native element fits. Prefer native elements first — 'no ARIA is better than bad ARIA'. Use it only to fill gaps.

localStorage vs sessionStorage vs cookies?

localStorage persists until cleared; sessionStorage lasts for the tab; cookies are small (~4KB) and sent to the server on every request. Prefer httpOnly cookies for auth tokens.

Why is the viewport meta tag important?

Without <meta name=viewport content='width=device-width, initial-scale=1'>, mobile browsers render at a fake ~980px width and zoom out, so your responsive CSS won't apply.