Frontend Engineer Interview Questions

Frontend Engineer interviews at top tech companies typically assess these competency areas:

These questions are drawn from real interview loops at FAANG and top-tier tech companies in 2025–2026. Click Practice now to run a full AI mock session for any question.

1. 1

   Implement a debounce function from scratch. When would you use throttle instead?

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2. 2

   Build an accessible autocomplete component with keyboard navigation.

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3. 3

   Explain the event loop, microtasks, and macrotasks with an example.

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4. 4

   How does React reconciliation work? What is the role of keys in lists?

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5. 5

   Design the front end for an Instagram-style infinite feed.

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6. 6

   What is the Critical Rendering Path? How do you optimize Largest Contentful Paint?

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7. 7

   Implement a deep clone function handling cycles, Maps, and Sets.

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8. 8

   Compare CSS Grid vs Flexbox — when do you reach for each?

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9. 9

   How do you ensure WCAG 2.1 AA compliance in a single-page app?

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10. 10

    Walk through hydration in Next.js — what causes mismatches and how do you fix them?

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• ✓Build 2–3 polished portfolio projects with measurable Lighthouse scores (95+).
• ✓Practice trivia: closures, hoisting, prototypes, this binding, promises.
• ✓Be ready to live-code in CodeSandbox with no autocomplete.
• ✓Know one component library deeply (Radix, MUI, Chakra) for design-system rounds.

Include these high-signal keywords in your Frontend Engineer resume to pass ATS filters at top companies.