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Preguntas 357 tarjetas Junior basics LLM y prompting What makes a prompt dependable instead of merely clever? Junior limits LLM y prompting What are tokens and context, and how do they affect an AI feature? Junior llm LLM y prompting What is an LLM, and why should an application treat its output as probabilistic rather than as ordinary business logic? Junior boundaries Arquitectura frontend y build How would you organize a frontend by features instead of by technical type? Junior responsibilities Arquitectura frontend y build What are the responsibilities of presentation, application, domain, and infrastructure layers in a frontend codebase? Junior lifecycle Backend y datos What are the main parts of an HTTP request and response, and what does it mean that HTTP is stateless? Junior basics Backend y datos When would you use a JOIN and when would you use GROUP BY in SQL? Junior story Behavioral y carrera Tell me about a project or accomplishment you are proud of. Walk me through it. Junior delegation Navegador y Web APIs What are event capturing, target, and bubbling phases, and how would you use event delegation? Junior choices Navegador y Web APIs How do cookies, localStorage, sessionStorage, and IndexedDB differ, and when would you choose each? Junior search DSA frontend Given a search box's text, how would you find the length of the longest substring without repeating characters, and what are the time and space costs? Junior stage Git, CI/CD y cloud What is the difference between a Docker image and a container, and why use a multi-stage build? Junior conflict Git, CI/CD y cloud How do you safely resolve a conflict during a rebase? Junior labels HTML, CSS y accesibilidad What makes a form control accessible, and why is a placeholder not a label? Junior grid HTML, CSS y accesibilidad When would you choose Flexbox over Grid, or Grid over Flexbox? Junior headings HTML, CSS y accesibilidad How would you structure a page so users can navigate its regions and headings? Junior responsive HTML, CSS y accesibilidad What does mobile-first responsive design mean in practice? Junior html HTML, CSS y accesibilidad Why should you prefer semantic HTML over styled div elements? Junior basics HTML, CSS y accesibilidad Which HTML choices provide a sound SEO foundation? Junior principles HTML, CSS y accesibilidad What is WCAG, and how should a frontend engineer use it? Junior sameness JavaScript y TypeScript When do `==`, `===`, `Object.is`, and SameValueZero differ? Junior modules JavaScript y TypeScript What makes an ES module different from a classic script? Junior coercion JavaScript y TypeScript How do JavaScript primitives, objects, and coercion differ? Junior erasure JavaScript y TypeScript What does TypeScript's type system guarantee at runtime, and what does it not? Junior const JavaScript y TypeScript What are the practical differences between `var`, `let`, and `const`? Junior layout Mobile y cross-platform How would you build a responsive mobile web layout that remains usable across phone and tablet widths? Junior statuses Redes y APIs How do HTTP methods and status-code classes communicate the intent and outcome of an API request? Junior push Redes y APIs Compare polling with a push-based connection for showing a changing status in a web UI. Junior capture Observabilidad What does a browser error-tracking SDK such as Sentry capture, and how would you verify that it is working? Junior baseline Python, backend y cloud Why do AI Engineer postings require Docker and at least one cloud platform even for application-layer roles? Junior service Python, backend y cloud What does a minimal production-ready service around an LLM call look like, and which tests does it need? Junior access Python, backend y cloud SQL is requested less in AI Engineer postings than in general tech postings. Which data skills still matter for the role? Junior forms React y frameworks UI What is the difference between controlled and uncontrolled form inputs? Junior flow React y frameworks UI What should a React render function do, and how does data normally flow through a component tree? Junior hooks React y frameworks UI What are the Rules of Hooks, and why do they exist? Junior updater React y frameworks UI When should a state update use the updater-function form? Junior authentication Seguridad y auth Why does CSRF occur, and what is a practical defense for cookie-authenticated requests? Junior boundary Seguridad y auth What is the same-origin policy, and what does CORS actually change? Junior encoding Seguridad y auth What is XSS, and how would you prevent it in a web application? Junior state Estado y data fetching What is the difference between client state and server state? Junior setup Estado y data fetching What does Redux Toolkit add to a Redux store setup? Junior design Estado y data fetching What belongs in URL state, and what are the basic URL query-string semantics? Junior scope Estilos y design systems What problem do CSS Modules solve, and what does local scoping mean? Junior properties Estilos y design systems How do CSS custom properties differ from ordinary preprocessor variables? Junior first Estilos y design systems What is the utility-first approach in Tailwind CSS, and how would you keep it maintainable? Junior feed System design frontend Design a news-feed UI that loads posts, supports reactions, and lets users compose a post. Junior autocomplete System design frontend Design a reusable autocomplete component for a search box. Junior strategy System design frontend Choose a rendering strategy for a content-heavy public page and an authenticated interactive dashboard. Junior ownership System design frontend How would you decide where state belongs in a frontend system? Junior choice Testing y calidad How do you choose among `getBy`, `queryBy`, and `findBy` in React Testing Library? Junior pyramid Testing y calidad What is the testing pyramid, and why should a suite contain fewer end-to-end tests than unit tests? Junior controls Componentes UI y machine coding Build an image carousel with previous/next controls, slide indicators, and optional autoplay. What accessibility and boundary behavior must be explicit? Junior plan Componentes UI y machine coding At the start of a 60-minute UI machine-coding round, how do you turn an ambiguous prompt into an implementation plan? Junior path Performance web What is the critical rendering path? Junior vitals Performance web What are the current Core Web Vitals, and what user experience does each one represent? Semi-senior conditions Agentes y MCP What is the core agent loop, and what controls must surround it? Semi-senior flow Agentes y MCP Walk through a safe function-calling request from the model to the final answer. Semi-senior architecture Agentes y MCP What does MCP standardize, and how is it different from a provider-specific function-calling API? Semi-senior modes RAG y retrieval Explain a RAG pipeline and the main ways it can fail. Semi-senior mode LLM y prompting When would you use structured output, and how is it different from asking for JSON in a prompt? Semi-senior api Arquitectura frontend y build Why should packages and features expose public entry points instead of allowing arbitrary deep imports? Semi-senior webpack Arquitectura frontend y build How would you choose between Vite and webpack for a frontend application? Semi-senior work Backend y datos How would you model an API endpoint that accepts work but completes it asynchronously? Semi-senior semantics Backend y datos How do GET, POST, PUT, PATCH, and DELETE differ, especially regarding safety and idempotency? Semi-senior costs Backend y datos What problem does a database index solve, and what trade-offs does it introduce? Semi-senior diagnosis Backend y datos What is the N+1 query problem, and how would you detect and fix it? Semi-senior aside Backend y datos Describe a cache-aside flow with Redis and the failure behavior you would design for. Semi-senior groups Backend y datos How do Redis Streams consumer groups help distribute work, and what must a worker do after processing? Semi-senior atomicity Backend y datos What does a transaction guarantee, and when should an application roll it back? Semi-senior conflict Behavioral y carrera Tell me about a conflict with a teammate and how you handled it. Semi-senior cancellation Navegador y Web APIs What does fetch reject for, how do you handle HTTP errors, and how do you cancel a request? Semi-senior api Navegador y Web APIs How is the browser's HTTP cache different from the Cache API, and how do cache headers influence your design? Semi-senior selection Navegador y Web APIs When would you choose MutationObserver, ResizeObserver, or IntersectionObserver? Semi-senior passing Navegador y Web APIs When should you use a dedicated web worker, and what constraints does worker communication impose? Semi-senior queue DSA frontend How would you traverse a nested menu DOM tree level by level to collect visible item labels, and why should a queue not use Array.shift() in a large traversal? Semi-senior deduplication DSA frontend You receive duplicate records from paginated API responses. How would you deduplicate them while preserving first-seen order, and when would you choose Map over Set? Semi-senior data DSA frontend How would you memoize an expensive derived value used by a filterable list, and what correctness problems can a cache introduce? Semi-senior pipeline Git, CI/CD y cloud What should a reliable CI/CD pipeline do from commit to production? Semi-senior rebase Git, CI/CD y cloud What is the difference between merging and rebasing, and when would you choose each? Semi-senior first HTML, CSS y accesibilidad When should you use ARIA, and when should you use native HTML instead? Semi-senior specificity HTML, CSS y accesibilidad How does CSS decide which conflicting declaration wins? Semi-senior validation HTML, CSS y accesibilidad How should client-side and server-side form validation work together? Semi-senior focus HTML, CSS y accesibilidad How do you make a custom interactive element keyboard accessible? Semi-senior content HTML, CSS y accesibilidad How should you provide alternative text for meaningful and decorative images? Semi-senior guards JavaScript y TypeScript Which JavaScript checks does TypeScript understand as narrowing? Semi-senior bind JavaScript y TypeScript When would you use `call`, `apply`, or `bind`? Semi-senior scope JavaScript y TypeScript What is a closure, and why does it outlive its creating function? Semi-senior unions JavaScript y TypeScript How do discriminated unions make state handling safer? Semi-senior model JavaScript y TypeScript Explain the JavaScript event loop without saying that JavaScript itself runs timers. Semi-senior inference JavaScript y TypeScript Why are generics better than `any` for reusable TypeScript functions? Semi-senior tdz JavaScript y TypeScript What is hoisted, and what does the temporal dead zone mean? Semi-senior closures JavaScript y TypeScript Why does a callback in a `var` loop often see the final index, and how do you fix it? Semi-senior chaining JavaScript y TypeScript Why must a promise returned inside a `.then` callback usually be returned? Semi-senior chain JavaScript y TypeScript How does property lookup through the JavaScript prototype chain work? Semi-senior checks JavaScript y TypeScript What changes when `strictNullChecks` is enabled? Semi-senior typing JavaScript y TypeScript What does structural typing mean in TypeScript, and how does it affect interfaces and type aliases? Semi-senior binding JavaScript y TypeScript How is `this` determined for regular functions, arrow functions, and constructors? Semi-senior exclude JavaScript y TypeScript What do `files`, `include`, and `exclude` control in a tsconfig, and what does `exclude` not do? Semi-senior intersection JavaScript y TypeScript How do union and intersection types differ? Semi-senior types JavaScript y TypeScript Which built-in utility types do you reach for when transforming an API model? Semi-senior cache LLM y prompting How do a model knowledge cutoff and prompt caching affect the design of a conversational product? Semi-senior cwv Mobile y cross-platform Which Core Web Vitals matter for a mobile web experience, and how would you investigate a regression? Semi-senior gestures Mobile y cross-platform How do you implement touch and drag interactions on the web without breaking scrolling or mouse and pen input? Semi-senior fundamentals Mobile y cross-platform What is React Native's basic rendering model, and how should a developer think about platform differences? Semi-senior etag Redes y APIs How would you make a cacheable API response fresh while avoiding unnecessary downloads? Semi-senior credentials Redes y APIs What happens during a CORS preflight, and what changes when credentials are included? Semi-senior pagination Redes y APIs What should a cursor-based GraphQL connection expose to make pagination usable? Semi-senior errors Redes y APIs What does GraphQL give a client that a fixed REST representation does not, and how should the client handle errors? Semi-senior design Redes y APIs What makes an HTTP API resource-oriented rather than a collection of action endpoints? Semi-senior vitals Observabilidad Why do you need RUM for Core Web Vitals, and how is it different from lab testing? Semi-senior production Observabilidad How would you design useful browser logs without creating noise or leaking sensitive data? Semi-senior dominates Python, backend y cloud Python shows up in most AI Engineer postings. What Python depth do interviewers actually probe beyond writing scripts? Semi-senior props React y frameworks UI When is Context a good fit, and what should you try first? Semi-senior purpose React y frameworks UI What is useEffect for, and when should you not use it? Semi-senior scope React y frameworks UI What does an Error Boundary catch, and what does it not catch? Semi-senior actions React y frameworks UI How do React 19 form actions work, and where does validation belong? Semi-senior keys React y frameworks UI What does a key tell React when rendering a list? Semi-senior snapshot React y frameworks UI Why can logging state immediately after calling its setter show the old value? Semi-senior contract React y frameworks UI What does Suspense do, and what does it not do? Semi-senior state React y frameworks UI What is the difference between useRef and useState? Semi-senior policy Seguridad y auth How would you design a CSP for an application, and what makes a policy strict? Semi-senior distinction Seguridad y auth What is the difference between OAuth 2.0 and OpenID Connect? Semi-senior attributes Seguridad y auth Which cookie attributes matter for an authentication session, and what does each protect? Semi-senior tradeoffs Seguridad y auth When would you choose an opaque server session over a JWT, and what are the trade-offs? Semi-senior stability Estado y data fetching What makes a good query key, and what bug appears when it omits a request input? Semi-senior boundaries Estado y data fetching Where should form state live, and why should it usually not be in server state or a global store? Semi-senior freshness Estado y data fetching What is the difference between freshness and cache lifetime in TanStack Query? Semi-senior invalidation Estado y data fetching When should a mutation invalidate a TanStack Query cache? Semi-senior entities Estado y data fetching When would you normalize Redux entities, and what does `createEntityAdapter` provide? Semi-senior slice Estado y data fetching Why use `createSlice`, and what does its reducer syntax actually mean? Semi-senior selectors Estado y data fetching How would you use selectors in Zustand, and why do they matter? Semi-senior api Estilos y design systems How should a reusable component expose styling customization without leaking its implementation? Semi-senior tradeoffs Estilos y design systems What trade-offs would you evaluate when choosing CSS-in-JS for a component library? Semi-senior preference Estilos y design systems How would you implement light, dark, and system themes without a flash of the wrong theme? Semi-senior feed System design frontend Design the API contract between a feed client and its backend. Semi-senior control System design frontend How do you prevent stale autocomplete responses from overwriting current results? Semi-senior scroll System design frontend Design infinite scrolling for a feed without duplicate pages or runaway requests. Semi-senior reset Testing y calidad What is the difference between clearing, resetting, and restoring Jest mocks? Semi-senior boundary Testing y calidad Where should you mock an API in a component or integration test, and what can go wrong when you mock an internal function? Semi-senior locators Testing y calidad How should you choose locators in a Playwright end-to-end test? Semi-senior behavior Testing y calidad What does it mean to test behavior rather than implementation details in RTL? Semi-senior uncontrolled Componentes UI y machine coding In a live round, implement an input that supports both controlled and uncontrolled usage. What rules prevent bugs when the mode changes or the value is initially missing? Semi-senior api Componentes UI y machine coding You have 45 minutes to build a reusable rating component. What API would you design before writing JSX, and which state would you keep internal versus expose? Semi-senior pagination Componentes UI y machine coding Build a reusable data table with pagination. Which state belongs in the table, what belongs in the data layer, and how do you prevent invalid page transitions? Semi-senior defer Performance web How do parser-blocking, async, defer, and module scripts differ for the critical path? Semi-senior boundaries Performance web When does code splitting improve performance, and when can it make a page slower? Semi-senior strategy Performance web How should you choose loading behavior for hero and below-the-fold images? Semi-senior rum Performance web Why can a Lighthouse result disagree with Real User Monitoring, and how should you use both? Semi-senior cls Performance web How do you prevent layout shifts in an asynchronously loaded feed? Semi-senior trace Performance web What is your workflow for diagnosing a janky interaction with Chrome DevTools? Senior agents Agentes y MCP What does it mean to program effectively with AI coding agents, and how do you verify their output? Senior exfiltration Agentes y MCP How do you stop an agent from exfiltrating data or running dangerous tools? Senior testing Evals y producción What would a useful evaluation strategy for an LLM feature or agent look like? Senior defense Evals y producción How would you defend an agent with private data and write-capable tools against prompt injection? Senior tuning RAG y retrieval How would you decide between RAG, prompting, and fine-tuning for a product requirement? Senior evolution LLM y prompting How do you evolve a structured-output contract without breaking an AI client? Senior design Agentes y MCP How do tool descriptions and schemas affect agent reliability? Senior agent Agentes y MCP When should you choose a deterministic workflow instead of an autonomous agent? Senior determinism Arquitectura frontend y build How can a build cache produce stale artifacts, and how do you prevent that? Senior graph Arquitectura frontend y build What is the difference between Nx's project graph and task graph, and why does it matter? Senior protocol Arquitectura frontend y build What problem does pnpm's `workspace:` protocol solve in a monorepo? Senior graph Arquitectura frontend y build How do `dependsOn`, `inputs`, and `outputs` make a Turborepo build both correct and fast? Senior boundary Arquitectura frontend y build How should a Vite application handle environment variables without leaking secrets? Senior order Backend y datos How would you choose the columns and order for a composite index? Senior retries Backend y datos Compare Read Committed, Repeatable Read, and Serializable isolation, and explain the application consequence of choosing Serializable. Senior tradeoffs Backend y datos When is batching preferable to a large join for solving N+1, and what risks remain? Senior counter Backend y datos Why is Redis INCR useful for a distributed counter, and what does atomic mean here? Senior modeling Backend y datos How do you decide between a relational database and a document-oriented NoSQL database? Senior alignment Behavioral y carrera Describe a project where you had to align multiple teams with different goals. Senior growth Behavioral y carrera Tell me about a failure or mistake and what you changed afterward. Senior authority Behavioral y carrera Tell me about a time you led an initiative without having formal authority. Senior others Behavioral y carrera Tell me about a time you helped someone grow or become more effective. Senior pressure Behavioral y carrera Tell me about a time you had multiple urgent priorities. How did you decide what to do first? Senior ux Navegador y Web APIs What does the Permissions API solve, and how should a product use it without treating permission state as permanent? Senior lifecycle Navegador y Web APIs Explain the service worker lifecycle and the main hazards when shipping an offline-capable PWA. Senior eviction Navegador y Web APIs How should an offline application reason about storage quotas, eviction, and persistence? Senior abort DSA frontend A route needs three independent API resources and may unmount before they finish. How would you run them, handle failure, and prevent obsolete results from updating the UI? Senior throttle DSA frontend Implement a utility for a search input or scroll handler: when do you choose debounce versus throttle, and what production behaviors should the API specify? Senior clone DSA frontend What should a deep-clone utility promise, and when is structuredClone() preferable to a JSON round trip? Senior traces Evals y producción Explain how you would run error analysis on an LLM system in production. Senior failing Evals y producción When your system started failing, how did you measure it, over how many cases, and what changed in the numbers? Senior secrets Git, CI/CD y cloud How should a pipeline manage environment-specific configuration and secrets? Senior iam Git, CI/CD y cloud What permissions and deployment steps are needed when API Gateway invokes Lambda? Senior site Git, CI/CD y cloud How would you serve a static frontend from S3 through CloudFront securely? Senior name HTML, CSS y accesibilidad What are name, role, state, and value, and why do they matter? Senior navigation HTML, CSS y accesibilidad How would you design a responsive navigation that remains accessible when it collapses? Senior order HTML, CSS y accesibilidad What accessibility risk comes from visually reordering Flexbox or Grid items? Senior resilience HTML, CSS y accesibilidad Which modern CSS features improve maintainability, and what guardrails would you use? Senior semantics JavaScript y TypeScript What does `await` actually do to an async function? Senior cancellation JavaScript y TypeScript Does a Promise cancel its underlying operation, and how should cancellation be designed? Senior interop JavaScript y TypeScript What problem does ESM/CommonJS interoperability create in a TypeScript package? Senior constraints JavaScript y TypeScript How do `keyof` and a constrained key generic make property access type-safe? Senior tasks JavaScript y TypeScript What order does this log, and why: `console.log('A'); Promise.resolve().then(() => console.log('B')); setTimeout(() => console.log('C'), 0); console.log('D')`? Senior access JavaScript y TypeScript Why might a library enable `noUncheckedIndexedAccess`? Senior combinators JavaScript y TypeScript When do you choose `Promise.all`, `allSettled`, `race`, or `any`? Senior mode JavaScript y TypeScript What does the `strict` compiler option do, and how should a team use it? Senior guards JavaScript y TypeScript How do you write a user-defined type guard, and what responsibility does it carry? Senior reasoning LLM y prompting How do you reason about token cost and latency before choosing a model for a feature? Senior tradeoffs Mobile y cross-platform What changed in React Native's New Architecture, and what would you verify before migrating a production app? Senior limits Mobile y cross-platform What does installing a PWA provide, and how would you communicate platform differences to product stakeholders? Senior rendering Mobile y cross-platform A React Native list of hundreds of rows scrolls poorly. What would you inspect and change first? Senior vary Redes y APIs Why can a dynamic CORS response be incorrect when a CDN caches it, and how do you prevent that? Senior pagination Redes y APIs How would you choose between offset pagination and cursor pagination for a changing, large collection? Senior requests Redes y APIs How do you decide whether an API request can be retried after a timeout? Senior sse Redes y APIs When would you choose WebSocket over Server-Sent Events, and what operational behavior must the client implement? Senior noise Observabilidad How do you design alerts that lead to action instead of alert fatigue? Senior bug Observabilidad How would you investigate an intermittent production bug that you cannot reproduce locally? Senior id Observabilidad A production Sentry stack trace still points into minified JavaScript. What would you check? Senior search RAG y retrieval Vector RAG was the first attempt at grounding a model in company data. What other ways do you have? Senior rag RAG y retrieval When would you NOT use RAG? Senior rerenders React y frameworks UI What happens when a Context provider's value changes, and how would you avoid unnecessary work? Senior cleanup React y frameworks UI How do Effect dependencies and cleanup work together? Senior handler React y frameworks UI How do you separate event-specific work from synchronization logic in a component? Senior condition React y frameworks UI How would you prevent an obsolete request from overwriting newer data in an Effect? Senior mismatch React y frameworks UI What causes hydration mismatches, and how should you fix them? Senior prop React y frameworks UI How do you expose a limited imperative API from a function component in React 19? Senior state React y frameworks UI When would you use a key outside a list? Senior actions React y frameworks UI What problem do React 19 Actions solve? Senior memoization React y frameworks UI What does the React Compiler change about manual memoization? Senior cleanup React y frameworks UI How would you manage refs for a dynamic list when the item count is unknown? Senior memoization React y frameworks UI When do useMemo and useCallback help, and when are they a smell? Senior commit React y frameworks UI What are the render and commit phases, and why must render stay pure? Senior ssr React y frameworks UI How do Suspense and streaming improve a server-rendered page? Senior remount React y frameworks UI Why can an Effect appear to run twice in development, and what is the correct fix? Senior values React y frameworks UI How do useTransition and useDeferredValue differ? Senior state React y frameworks UI How does useActionState change form code in React 19? Senior boundary React y frameworks UI What does use client mean in the Next.js App Router? Senior context React y frameworks UI What is React 19's use API, and how is it different from ordinary Hooks? Senior cache React y frameworks UI Why must a Promise passed to use in a Client Component be cached? Senior boundaries Seguridad y auth What must an API validate before accepting a JWT access token? Senior client Seguridad y auth How should a browser application use OAuth authorization code flow safely? Senior design Seguridad y auth How would you design rate limiting for login and API endpoints? Senior lifecycle Seguridad y auth How would you manage application and CI/CD secrets across their lifecycle? Senior rotation Seguridad y auth What is session fixation, and where should a session identifier be rotated? Senior forms Estado y data fetching When would you choose controlled inputs versus an uncontrolled form library approach? Senior reconciliation Estado y data fetching How do you prevent a form draft from being overwritten when fresh server data arrives? Senior abort Estado y data fetching How can an asynchronous Jotai atom avoid applying obsolete work? Senior atoms Estado y data fetching How do Jotai derived atoms track dependencies, and what identity trap should you know? Senior rollback Estado y data fetching How do you implement a safe optimistic update? Senior boundaries Estado y data fetching Where should asynchronous logic live in a Redux Toolkit application? Senior keys Estado y data fetching How does RTK Query deduplicate requests and expire unused cache entries? Senior tags Estado y data fetching Explain `providesTags` and `invalidatesTags` in RTK Query. Senior architecture Estilos y design systems How would you structure CSS so a design system, application styles, and third-party styles remain predictable? Senior versioning Estilos y design systems What should count as a breaking change when versioning a design-system package? Senior hierarchy Estilos y design systems How would you design a token hierarchy for multiple brands and color modes? Senior consistency System design frontend How would you keep a chat UI consistent while messages are sent optimistically and events arrive out of order? Senior transport System design frontend Design the realtime layer for a chat application and justify the transport. Senior editor System design frontend Design a collaborative document editor for multiple simultaneous users. Senior reconciliation System design frontend Extend the collaborative editor to support offline edits and later reconciliation. Senior budget System design frontend Set a performance budget for a new frontend product and explain how you would enforce it. Senior feed System design frontend Design rendering for a feed with thousands of variable-height posts and media. Senior testing Testing y calidad What should an accessibility test strategy include beyond an automated scan? Senior gates Testing y calidad How should code coverage influence CI quality gates? Senior tests Testing y calidad A test passes locally but fails intermittently in CI. How do you investigate and fix it? Senior waits Testing y calidad How would you make a Playwright suite reliable when the UI updates asynchronously? Senior refactor Testing y calidad What does TDD mean in practice, and when would you adapt it rather than follow it rigidly? Senior scope Testing y calidad When is visual regression testing worth its maintenance cost, and how would you keep it deterministic? Senior async Componentes UI y machine coding Implement an async autocomplete that searches as the user types. How do you handle debouncing, stale responses, loading/error/empty states, and selection? Senior model Componentes UI y machine coding You are asked to code an editable combobox. Explain the DOM focus model, the popup semantics, and the minimum keyboard interactions you would implement. Senior tabs Componentes UI y machine coding Build a Tabs component as a compound API such as `<Tabs><Tabs.List>...</Tabs.List><Tabs.Panel>...</Tabs.Panel></Tabs>`. How do you keep the parts coordinated without coupling consumers to implementation details? Senior trap Componentes UI y machine coding Build an accessible modal in a machine-coding round. What must happen to focus, keyboard input, labeling, and the content behind it? Senior state Componentes UI y machine coding Your paginated table is revisited, filtered, and used with the browser Back button. What would you put in component state versus the URL, and how would you keep the UI consistent? Senior lcp Performance web How would you investigate and improve a poor LCP score on a product page? Senior tradeoffs Performance web How can web fonts affect LCP and CLS, and what is a responsible loading strategy? Senior layout Performance web What is layout thrashing, and how would you fix it? Senior inp Performance web What would you do when users report delayed clicks even though the page loads quickly? Senior tradeoffs Performance web What does list virtualization solve, and what trade-offs must you account for? Staff / Lead limitations Evals y producción How would you use an LLM-as-judge without turning it into an unquestioned source of truth? Staff / Lead boundaries Evals y producción How would you diagnose whether a bad RAG answer came from retrieval or generation? Staff / Lead idempotency Agentes y MCP How do you prevent retries or repeated tool calls from duplicating a consequential side effect? Staff / Lead migration Arquitectura frontend y build How would you migrate a large frontend from a legacy build or folder structure without stopping delivery? Staff / Lead boundaries Arquitectura frontend y build When is a micro-frontend architecture justified, and what boundary would you choose? Staff / Lead runtime Arquitectura frontend y build Explain how webpack Module Federation loads a remote module and shares dependencies. Staff / Lead tradeoffs Arquitectura frontend y build How would you evaluate Turbopack against an existing webpack or Vite build? Staff / Lead api Backend y datos How would you make a retried create operation safe when the client times out after the server may have committed it? Staff / Lead processing Backend y datos What properties should a reliable queue consumer have when a message can be delivered more than once? Staff / Lead manager Behavioral y carrera Tell me about a time you disagreed with your manager or a senior stakeholder. Staff / Lead end Behavioral y carrera Tell me about a complex project you owned from discovery through delivery. Staff / Lead upgrades Navegador y Web APIs How would you design IndexedDB schema upgrades for a long-lived application with multiple tabs? Staff / Lead strategy Navegador y Web APIs How would you choose caching strategies for a PWA serving assets, documents, and API data? Staff / Lead treewalker DSA frontend For a large document, how would you collect only text nodes under a content root while pruning subtrees marked as private, and what would you consider before choosing manual recursion? Staff / Lead ordering DSA frontend Why can a promise callback run before a zero-delay timer, and how can excessive microtasks hurt a responsive interface? Staff / Lead strategy Git, CI/CD y cloud How would you choose between trunk-based development, GitHub Flow, and Gitflow? Staff / Lead rollouts Git, CI/CD y cloud How do feature flags complement continuous delivery, and what operational risks do they introduce? Staff / Lead state Git, CI/CD y cloud Explain the basic Terraform workflow and why state matters in CI. Staff / Lead regions HTML, CSS y accesibilidad When would an `aria-live` region be appropriate, and how would you avoid overwhelming users? Staff / Lead hover HTML, CSS y accesibilidad What should an accessible focus indicator and hover-triggered disclosure do? Staff / Lead parallelism JavaScript y TypeScript How would you limit concurrency when processing many asynchronous jobs? Staff / Lead resolution JavaScript y TypeScript How do `module`, `moduleResolution`, and the runtime or bundler need to agree? Staff / Lead differences JavaScript y TypeScript What should a full-stack engineer avoid assuming when comparing the browser and Node.js event loops? Staff / Lead references JavaScript y TypeScript When are TypeScript project references useful in a large repository? Staff / Lead bare Mobile y cross-platform When would you choose Expo tooling over a React Native project managed directly with native tooling? Staff / Lead strategy Mobile y cross-platform How would you design offline behavior for a PWA, and what must not be promised to users? Staff / Lead evolution Redes y APIs How would you evolve a public REST API without forcing every consumer to migrate at once? Staff / Lead evolution Redes y APIs Why does GraphQL usually evolve a schema instead of publishing v2, and how do you retire a field safely? Staff / Lead errors Redes y APIs What makes an API error contract useful to both machines and humans? Staff / Lead correlation Observabilidad How would you make observability data support safe releases and fast rollback decisions? Staff / Lead sampling Observabilidad How would you introduce session replay responsibly and still make it useful for debugging? Staff / Lead propagation Observabilidad Explain how distributed tracing connects a browser request to work in backend services, and what makes the data useful. Staff / Lead adoption React y frameworks UI How would you introduce React Compiler into a large existing application? Staff / Lead segments React y frameworks UI What architectural role do layouts, loading files, and error files play in the App Router? Staff / Lead policy Seguridad y auth How would you review a credentialed CORS design for a multi-tenant API? Staff / Lead controls Seguridad y auth What controls would you put around third-party dependencies and the software supply chain? Staff / Lead failure Estado y data fetching What should the UI do when an optimistic mutation succeeds but reconciliation fails? Staff / Lead mutations Estado y data fetching How do concurrent optimistic mutations change your design? Staff / Lead query Estado y data fetching How would you choose between RTK Query and TanStack Query? Staff / Lead key Estado y data fetching How should URL filters interact with a server-state cache? Staff / Lead boundaries Estilos y design systems How would you migrate a large application from a runtime CSS-in-JS system while keeping teams shipping? Staff / Lead theme Estilos y design systems How would you share a Tailwind-based visual language across several applications without coupling their build systems too tightly? Staff / Lead chat System design frontend Design accessibility constraints for a realtime chat UI with notifications and an infinite message history. Staff / Lead versioning System design frontend Design an API-contract strategy that lets independently deployed frontend and backend teams evolve safely. Staff / Lead start System design frontend Architect internationalization for a frontend product that will add locales, RTL languages, and culturally different formats. Staff / Lead feed System design frontend Design a resilient feed for intermittent connectivity, partial failures, and stale cached data. Staff / Lead boundaries Testing y calidad How would you decide whether a requirement belongs in a unit, integration, contract, or end-to-end test? Staff / Lead matrix Testing y calidad How would you design a Playwright browser matrix and CI schedule for a product team? Staff / Lead scale Testing y calidad How would you manage flakiness across a large organization without normalizing retry-until-green? Staff / Lead management Componentes UI y machine coding During a component review, you find that every popup implements its own focus trap. How would you design a shared focus-management primitive without making dialogs and comboboxes behave identically? Staff / Lead design Performance web How would you design performance budgets that a team will actually use? Staff / Lead vitals Performance web What would a trustworthy field-performance measurement plan include? Staff / Lead preload Performance web How would you decide between preloading and prefetching a split chunk? Staff / Lead priorities Performance web How would you govern resource hints and priorities across a large product? Architect management Evals y producción How should an organization manage model, prompt, retrieval, and tool changes in production? Architect governance Evals y producción What should an organization standardize across teams building AI features? Architect agent Agentes y MCP At an architecture review, what evidence would justify not building an agent? Architect runtime Arquitectura frontend y build How do you design configuration so one frontend artifact can be promoted across environments safely? Architect model Arquitectura frontend y build What failure and compatibility model should an organization define before adopting federated micro-frontends? Architect build Arquitectura frontend y build What changes when you configure a build for a reusable frontend library instead of an application? Architect governance Arquitectura frontend y build What governance keeps a frontend monorepo from becoming a distributed monolith? Architect boundary Backend y datos How would you preserve correctness when one request must update a database and publish a queue event? Architect practice Behavioral y carrera Tell me about a change you made that improved how multiple teams worked, not just one project. Architect coordination Navegador y Web APIs How would you coordinate state across tabs, workers, and service workers while preserving correctness and responsiveness? Architect limit DSA frontend Design a utility that maps many browser tasks—such as image metadata reads or page prefetches—while never exceeding a caller-supplied concurrency limit. What guarantees should it provide? Architect canary Git, CI/CD y cloud When would you choose all-at-once, blue/green, canary, or linear deployment? Architect privilege Git, CI/CD y cloud How do you apply least privilege to CI/CD and AWS workloads? Architect layout HTML, CSS y accesibilidad How would you choose breakpoints for a component library used in many layouts? Architect route HTML, CSS y accesibilidad How should a client-rendered route change be made understandable to keyboard and screen-reader users? Architect scale JavaScript y TypeScript How would you design TypeScript module boundaries for a multi-team platform? Architect readiness Mobile y cross-platform What release-readiness concerns must a cross-platform team cover before submitting a mobile app to Apple and Google Play? Architect governance Redes y APIs How would you govern many APIs so that local design choices remain compatible at organization scale? Architect design Redes y APIs Design idempotency for a payment-like POST endpoint that clients may retry after losing the response. Architect backpressure Redes y APIs What distributed-systems concerns appear when scaling a WebSocket or SSE service beyond one process? Architect contract Observabilidad What should an organization-wide observability contract standardize across frontend and backend teams? Architect boundary React y frameworks UI How would you decide where data fetching belongs in a Next.js App Router tree? Architect rsc React y frameworks UI How are SSR and React Server Components different? Architect response Seguridad y auth A scanner reports a vulnerability in a transitive dependency. How do you decide what to do? Architect radius Seguridad y auth How would you reduce credential blast radius across a large engineering organization? Architect tradeoff Estado y data fetching Why does RTK Query not provide a fully normalized cross-query cache, and what follows from that? Architect scale Estado y data fetching How would you define state ownership and synchronization boundaries across a large product? Architect model Estilos y design systems How would you design the operating model for a design system used by many product teams? Architect state System design frontend Design ownership and synchronization when the same product is open in several tabs. Architect observability System design frontend Create an organization-wide frontend performance system that keeps multiple teams within budget. Architect communication System design frontend How do you communicate trade-offs in a frontend system-design interview when requirements are incomplete? Architect system Testing y calidad What should an organization-wide quality gate measure besides test pass rate and line coverage? Architect snapshots Testing y calidad How would you prevent a UI change from escaping when visual pixels and accessibility semantics can fail independently? Architect list Componentes UI y machine coding Design a virtualized list component for a large dataset. What contract and implementation trade-offs would you clarify before coding? Architect scale Performance web How would you make performance a durable architectural property across many teams? Architect observer Performance web When would you use PerformanceObserver, and what limitations should your measurement design acknowledge?