25 Frontend Engineer Interview Questions

How do you decide when to use client-side rendering vs. server-side rendering vs. static generation?

Walk me through how you'd optimize a React app that has become slow to render.

Explain the virtual DOM — what problem does it solve and what are its limitations?

How do you approach accessibility in a new component? What do you check?

Describe a time you improved Core Web Vitals on a production site. What did you change?

How do you handle state management in a large React application?

What's your strategy for managing CSS at scale — modules, Tailwind, styled-components?

How would you implement infinite scroll without causing layout thrash?

Explain the difference between useEffect and useLayoutEffect — when do you use each?

How do you test UI components? What's your philosophy on what deserves a test?

How would you build a design system from scratch for a team of 10 engineers?

Walk me through how a browser renders a page from HTML to pixels.

How do you handle form validation in a complex multi-step form?

Describe your approach to responsive design — mobile-first or desktop-first? Why?

How would you implement drag-and-drop from scratch without a library?

What's your strategy for feature flags and A/B testing on the frontend?

How do you keep bundle size under control as a project grows?

Describe the most complex UI component you've ever built.

How do you handle real-time updates — WebSockets, SSE, or polling?

What's your approach to error boundaries and graceful degradation?

How would you build a table component that handles 100k rows?

Explain how you'd implement a dark mode toggle that persists across sessions.

How do you ensure consistent cross-browser behavior in your CSS?

Describe your experience with web performance profiling tools.

How do you document components for other developers in your team?