Frontend interviews at top companies are now as rigorous as backend interviews — and in some ways harder, because the surface area is wider (DOM, JS, browser, network, framework, accessibility, performance). This cheat sheet covers the 12 topics that come up in 80% of loops, with the angle each company tends to take.
JavaScript Fundamentals
- Closures, scope, and the temporal dead zone — expect a code-trace question.
- Event loop, microtasks vs macrotasks — be ready to predict the log order of Promise + setTimeout.
- Prototype chain, this binding, and arrow-function differences.
- Polyfills — be able to implement bind, debounce, throttle, and Promise.all from memory.
React Internals
Reconciliation and Keys
Be ready to explain why keys matter (stable identity across renders) and what happens when you use the array index as a key (re-mounts on reorder, lost state). Interviewers love asking about list-reorder bugs.
useEffect Dependencies
Be ready to debug a useEffect with a missing dependency and to explain when useCallback / useMemo are worth the overhead (rarely — only when the child component is genuinely expensive or memoised).
Concurrent Rendering Mental Model
If you say you know React 18+, expect questions on Suspense, transitions, and why concurrent rendering can interrupt a render. You do not need to know the scheduler internals, but you need to know what is interruptible vs not.
Frontend System Design
Design a Virtualised List
Recurring prompt at Meta, Google, Stripe. Drive: viewport size, item height (fixed or variable), buffer rows, scroll-anchor strategy, accessibility for screen readers. The interesting trade-off is variable item heights — you need a measurement cache.
Design an Autocomplete
Drive: debounce strategy, request cancellation, caching by query prefix, keyboard navigation, ARIA-combobox role. Interviewers love it when you mention race conditions on rapid typing.
Performance Budget
Expect questions about Core Web Vitals (LCP, CLS, INP), why bundle size matters, and how you would diagnose a slow page in production. Mention RUM, Lighthouse, and the Performance API.
InterviewLift's frontend track includes a code-trace drill set, a React-internals quiz, and a structured frontend-system-design mock with the rubric used at Meta and Stripe. The drill set alone catches the JavaScript trick questions most candidates only learn about during the live interview.
Reviewed by the InterviewLift customer-success team, who prepare candidates for real interviews every week.
Try Jarvis free: 15 questions
No card needed. Use it in your next practice round or interview.