✅ Part 2: Top 30 Advanced HTML Interview Questions and Answers (For Experienced Developers)

Payal PorwalPayal Porwal
6 min read

Table of contents

Introduction:
Welcome to Part 2 of our frontend interview series! In this article, we cover 30 advanced-level HTML interview questions with detailed answers for experienced frontend developers. These questions go beyond the basics and focus on real-world scenarios, performance, accessibility, SEO, and HTML5 APIs.

🔶 1. What are custom data attributes in HTML5?

Answer:
Custom data attributes allow you to store extra data in HTML elements using the data- prefix.
Example:

<div data-user-id="123" data-role="admin"></div>

They are useful for passing data to JavaScript without affecting layout or functionality.

🔶 2. What are semantic HTML tags and why are they important?

Answer:
Semantic tags like <article>, <section>, <main>, <nav>, and <aside> provide meaning to the content. They improve:

  • Code readability

  • SEO

  • Accessibility for screen readers and assistive devices

🔶 3. What is ARIA in HTML and when should we use it?

Answer:
ARIA (Accessible Rich Internet Applications) attributes improve accessibility.
Examples:

  • aria-label, aria-hidden, aria-expanded
    Used when native HTML elements don’t offer enough accessibility by default.

🔶 4. What is the difference between <section> and <div>?

Answer:

  • <section> is semantic, used for grouped content with a heading.

  • <div> is non-semantic, used for general layout with no meaning.
    Use <section> for structured content blocks.

🔶 5. How does the HTML parsing process work in browsers?

Answer:
HTML is parsed by the browser in a top-down manner. The browser builds a DOM (Document Object Model) tree from the HTML. It uses the parser engine to:

  • Tokenize input

  • Build nodes

  • Render layout

🔶 6. What is the difference between defer and async attributes in <script>?

Answer:

  • defer: downloads the script in parallel, executes after HTML is parsed.

  • async: downloads and executes script immediately, may block parsing.
    Use defer for scripts that depend on the DOM.

🔶 7. What are the different types of HTML doctypes?

Answer:
Some common doctypes:

  • <!DOCTYPE html> — HTML5

  • <!DOCTYPE HTML PUBLIC ...> — HTML 4.01
    Doctype tells the browser how to render the page (standards or quirks mode).

🔶 8. What is Shadow DOM?

Answer:
Shadow DOM is a part of Web Components. It lets you encapsulate styles and markup so they don’t clash with the rest of the page.
Example:

<my-component></my-component>

The internal DOM is hidden from the main page.

🔶 9. What is the use of the <template> tag?

Answer:
It is used to define HTML that is not rendered until it is called with JavaScript. Helps in reusing and rendering dynamic content.

🔶 10. How can you improve page load performance using HTML?

Answer:

  • Use defer and async for scripts

  • Lazy-load images

  • Minimize inline styles

  • Compress HTML using gzip

  • Use CDN for static assets

🔶 11. How do you make a website mobile-friendly using HTML?

Answer:

  • Use the <meta name="viewport"> tag

  • Use responsive layout techniques

  • Avoid fixed widths
    Example:

<meta name="viewport" content="width=device-width, initial-scale=1.0">

🔶 12. What is lazy loading in HTML?

Answer:
Lazy loading delays loading of images or videos until they are in the viewport.
Example:

<img src="img.jpg" loading="lazy" alt="image">

🔶 13. What are web components in HTML?

Answer:
Web components allow reusable custom elements with:

  • Shadow DOM

  • HTML templates

  • Custom elements API

🔶 14. What are contenteditable and spellcheck attributes?

Answer:

  • contenteditable="true" makes any element editable

  • spellcheck="true" checks spelling in text input or content

🔶 15. How do you implement accessibility in forms?

Answer:

  • Use <label> properly linked with for

  • Use aria-* attributes when needed

  • Ensure tab order is logical

  • Provide proper alt text for icons

Answer:
It defines the relationship between the current page and the linked document.
Example:

<link rel="stylesheet" href="style.css">

🔶 17. How is SEO impacted by HTML structure?

Answer:
SEO improves when:

  • Proper heading hierarchy is used (<h1> to <h6>)

  • Semantic tags are used

  • Descriptive titles, meta descriptions, and alt attributes are present

🔶 18. What is progressive enhancement in HTML?

Answer:
It means starting with basic HTML content that works on all browsers, then adding advanced CSS or JavaScript for better experience on modern browsers.

🔶 19. What is the purpose of <noscript> tag?

Answer:
It provides fallback content for users with JavaScript disabled.
Example:

<noscript>Please enable JavaScript to use this feature.</noscript>

🔶 20. Can we put <script> inside <body>? Why?

Answer:
Yes, you can. Putting it at the end of <body> ensures the DOM is fully loaded before the script runs, improving performance.

🔶 21. What are the security risks in HTML?

Answer:

  • Cross-site scripting (XSS) from user inputs

  • Insecure iframes

  • Injection attacks
    Mitigation: Sanitize input and use proper headers.

🔶 22. How can you improve accessibility for screen readers?

Answer:

  • Use semantic HTML

  • Use ARIA attributes correctly

  • Avoid visual-only cues (like color only)

  • Use alt text for images

🔶 23. What is the difference between <strong> and <b>?

Answer:

  • <strong> is semantic and means important text

  • <b> is for styling bold text without semantic meaning

🔶 24. How do you embed audio and video in HTML5?

Answer:

<video controls>
  <source src="video.mp4" type="video/mp4">
</video>

<audio controls>
  <source src="audio.mp3" type="audio/mpeg">
</audio>

🔶 25. What is the use of the srcset attribute in <img>?

Answer:
srcset allows the browser to choose the best image size based on screen size and resolution.
Improves performance and mobile experience.

🔶 26. How does HTML handle character encoding?

Answer:
Use the <meta charset="UTF-8"> tag to define character encoding. This ensures correct display of special symbols.

🔶 27. What is a content security policy (CSP) and how is it added in HTML?

Answer:
CSP helps prevent XSS attacks. It is added using a meta tag or HTTP header.
Example:

<meta http-equiv="Content-Security-Policy" content="default-src 'self';">

🔶 28. What is the use of the <mark>, <kbd>, and <code> tags?

Answer:

  • <mark> highlights text

  • <kbd> shows keyboard input

  • <code> shows code snippet (inline)

🔶 29. What is the difference between hidden and display: none?

Answer:

  • hidden is an HTML attribute that hides elements

  • display: none is a CSS style
    Both hide content, but display: none is more flexible in styling.

🔶 30. How do HTML5 APIs help in frontend development?

Answer:
HTML5 includes powerful APIs like:

  • Geolocation API

  • Drag and Drop API

  • Web Storage API (localStorage/sessionStorage)

  • Canvas API
    These allow advanced functionality without external libraries.

✅ Conclusion

These advanced HTML questions are perfect for experienced frontend developers preparing for senior-level interviews. Understanding these topics not only boosts confidence but also helps in writing clean, accessible, and high-performance HTML code.

👉 In Part 3, we will cover CSS interview questions and answers — from beginner to expert level.

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Payal Porwal
Payal Porwal

Hi there, tech enthusiasts! I'm a passionate Software Developer driven by a love for continuous learning and innovation. I thrive on exploring new tools and technologies, pushing boundaries, and finding creative solutions to complex problems. What You'll Find Here On my Hashnode blog, I share: 🚀 In-depth explorations of emerging technologies 💡 Practical tutorials and how-to guides 🔧Insights on software development best practices 🚀Reviews of the latest tools and frameworks 💡 Personal experiences from real-world projects. Join me as we bridge imagination and implementation in the tech world. Whether you're a seasoned pro or just starting out, there's always something new to discover! Let’s connect and grow together! 🌟