Frontend interviews trade some of the algorithm volume for live UI coding, JavaScript/TypeScript depth, browser internals, performance budgets, and accessibility. Expect at least one round in a CodeSandbox or StackBlitz environment building or fixing a small component.
Technical screen (45–60 min). Live coding in a browser-based IDE: implement a debounce, build an autocomplete, fix a stale-closure bug, or refactor a class component to hooks.
System design — frontend (45–60 min). Design Twitter feed, an autocomplete, a multi-step form, or a kanban board. Focus on data fetching, state management, rendering strategy, and a11y.
CS / JS fundamentals (45 min). Event loop, microtasks vs macrotasks, prototype chain, this binding, closures, async iteration, generators, Web Workers.
Browser & perf (45 min). Critical rendering path, layout vs paint vs composite, INP/LCP/CLS, code splitting, hydration, server components vs client.
Behavioural (45 min). Cross-functional collaboration with designers, PMs, backend; pixel-pushing vs shipping; perf-vs-feature trade-offs.
Top Frontend Engineer technical questions
These are pulled from interview-debrief patterns we see most often across Engineering roles. They are not memorization fodder — interviewers reword them constantly. Practice the underlying skill, not the wording.
Implement Promise.all from scratch. Then implement Promise.allSettled.
Build a typeahead component that handles slow APIs, request races, and keyboard navigation.
Why does this useEffect fire infinitely? (paste broken hook code) — diagnose and fix.
Explain how React reconciliation works. When do keys actually matter?
Memo, useMemo, useCallback — when is each the wrong tool?
Walk through what happens between typing a URL and seeing first paint.
How would you reduce LCP on a Next.js page from 4.2s to under 2s?
Implement a virtual list (windowing) for 100k rows. What changes for variable-height rows?
Design state management for a multi-tab spreadsheet — Redux, Zustand, Jotai, or context? Defend the choice.
Make this component accessible: a custom dropdown built from divs. What ARIA roles, keyboard handling, and focus management are required?
Explain CSS containment and where it helps in a real app.
How do you debug a memory leak in a long-lived single-page app?
Behavioural questions
Tell me about a UI you shipped that turned out to be confusing for users. How did you respond?
Describe a perf optimization that made a measurable difference. Numbers, please.
When have you pushed back on a design? What did you propose instead?
Walk through a tricky cross-browser bug you fixed.
Preparation tips for Frontend Engineer candidates
**Practice live coding in StackBlitz, not LeetCode.** Frontend interviewers want to see you wire up components, fetch data, and handle loading/error states fluently.
**Have one strong answer to 'how do you measure perf'.** Concrete numbers (LCP, INP, CLS, bundle size) and tools (Lighthouse, Chrome perf panel, web-vitals lib).
**Know the React rendering model deeply.** When does a component re-render, what makes it expensive, what does Server Components actually change.
**Bring a11y vocabulary.** ARIA roles, focus trap, keyboard navigation, live regions — most candidates wave their hands; few can name the right pattern.
Practice with the AI mock interviewer
Panor's AI Job Assistant runs voice-based mock interviews tuned to the Frontend Engineer role. It ad-libs follow-up questions, calls out red flags in your answers, and produces a transcript with rubric-graded feedback. Resume × JD matching is also included — paste a target job description and the assistant rewrites your bullets in STAR format with keyword alignment scoring.
Strong candidates with relevant experience generally need 4–6 weeks of focused prep for a competitive Frontend Engineer loop. Career switchers should plan on 8–12 weeks, weighted heavily toward the engineering fundamentals.
Do I need to grind LeetCode?
For most Frontend Engineer loops in 2026, depth on a curated set of 60–80 problems beats grinding 400. Focus on the patterns the questions above test, not problem volume.
Is the format the same at startups vs Big Tech?
No. Big Tech tends to over-index on coding and system design; startups put more weight on judgement, speed, and 'will this person carry the team'. Read the JD and ask the recruiter for the explicit loop structure — they will tell you.