Technical Interviewer’s Questions

1. How do you approach responsive design for different screen sizes?

Great Response: "I use a mobile-first approach, starting with core functionality and progressively enhancing for larger screens. I implement flexible grids with CSS Grid and Flexbox rather than fixed pixels, and use strategic breakpoints based on content needs rather than specific devices. I test across actual devices during development, not just browser emulation. For complex layouts, I build responsive components that adapt independently rather than creating entirely different designs for each breakpoint. I also use responsive typography with clamp() or viewport units to ensure text scales appropriately without causing accessibility issues."

Mediocre Response: "I use media queries to create breakpoints for mobile, tablet, and desktop. I generally design desktop-first since that's where most of our users are, then adjust for smaller screens. I rely on Bootstrap's responsive grid system to handle most of the layout changes, and test in Chrome DevTools' device mode to make sure everything looks good."

Poor Response: "I set up a few standard breakpoints at common screen sizes and create alternate CSS for each. I usually design separate versions for mobile and desktop, hiding elements that don't fit well on smaller screens. I find it's faster to just build fixed-width layouts for each major device category than trying to make everything fluid. If we need to support an unusual screen size later, I can add another breakpoint."

2. Explain your approach to optimizing a web application's performance.

Great Response: "I focus on both perceived and actual performance. First, I measure using Lighthouse and WebPageTest to establish baselines. For frontend optimizations, I implement code splitting to reduce initial bundle size, use resource hints like preload for critical assets, and lazy-load non-critical components. I optimize image delivery using modern formats like WebP/AVIF with appropriate srcsets and sizes, and implement responsive loading strategies. For CSS, I eliminate render-blocking resources and ensure critical CSS is inlined. I also implement proper caching strategies using service workers where appropriate. Throughout development, I set performance budgets and monitor metrics like FCP, LCP, and TBT to ensure we're maintaining good UX."

Mediocre Response: "I compress images using tools like TinyPNG, minify CSS and JavaScript files, and try to combine requests where possible. I check for performance issues in Chrome DevTools and fix any obvious bottlenecks. I also use lazy loading for images and implement some basic caching. If we're using a framework like React, I'll try to code-split where it makes sense."

Poor Response: "I optimize images before adding them to the project and use minification tools on our build process for the CSS and JS. If users complain about slowness, I'll check what's causing it in the network tab. Usually, the backend team needs to optimize their APIs if there are performance issues, so I make sure to document any slow requests we're seeing. Otherwise, modern browsers and devices are pretty fast, so basic optimizations are usually enough."

3. How do you ensure your UI components are accessible?

Great Response: "I build accessibility in from the start using WCAG 2.1 AA standards as a minimum baseline. I ensure semantic HTML structure with appropriate landmarks and headings hierarchy, implement proper keyboard navigation with visible focus states, and use ARIA attributes only when native HTML semantics aren't sufficient. For interactive components, I test with keyboard-only navigation and screen readers like NVDA or VoiceOver. I maintain sufficient color contrast ratios (at least 4.5:1 for normal text) and don't rely solely on color to convey information. I also create accessible forms with proper labels, error messages, and instructions. Throughout development, I use tools like axe DevTools alongside manual testing to catch issues early, and I document accessibility features in component libraries for team consistency."

Mediocre Response: "I follow basic accessibility guidelines like adding alt text to images, making sure there's enough color contrast, and testing tab navigation. I use the accessibility checker in the browser dev tools to find obvious issues. For complex components like modals or dropdowns, I look up ARIA patterns to make sure they're implemented correctly. I try to test with a screen reader when I have time."

Poor Response: "I add alt text to images and make sure color contrast meets minimum requirements according to the automatic checker. For more complex components, I use UI libraries that are supposed to be accessible by default, so I don't have to worry too much about implementation details. If QA finds any accessibility issues, I'll fix them before we ship."

4. Describe your process for designing and implementing a new UI component.

Great Response: "I start by understanding the component's purpose, user needs, and where it fits within our design system. I collaborate with designers to clarify requirements and edge cases, then create low-fidelity prototypes to validate the interaction model. For implementation, I first establish the component's API with clear props/inputs and document expected behaviors. I write the component using a TDD approach with unit tests for logic and Storybook for visual testing. I implement the UI with semantic HTML, ensuring it's accessible and responsive by default. I follow the principle of progressive enhancement, ensuring core functionality works without JS when possible. I seek feedback from team members and address any usability concerns before finalizing. Throughout development, I document the component with usage examples, edge cases, and accessibility considerations for other developers."

Mediocre Response: "I review the design specs and ask questions if anything is unclear. Then I create the component using our framework of choice, implementing the visual design first and then adding the functionality. I make sure it works across different screen sizes and test it in our main browsers. Once it's working, I add it to our component library with basic documentation about how to use it."

Poor Response: "I implement the component based on the mockups provided by the design team. I usually start by looking for similar components in our existing codebase or online libraries to adapt rather than building from scratch. If I run into any technical limitations, I'll let the designer know we need to simplify. Once the component looks right and functions correctly in the main use case, I submit it for review."

5. How do you handle browser compatibility issues in your projects?

Great Response: "I approach browser compatibility strategically based on project requirements and user analytics. I start by establishing a clear browser support matrix with the team, identifying which browsers and versions we need to fully support versus providing a degraded experience. I use feature detection rather than browser detection, implementing graceful degradation and progressive enhancement where appropriate. For CSS, I leverage PostCSS with autoprefixer and appropriate browserslist configurations to handle vendor prefixes and polyfills. For JavaScript, I use transpilation with Babel configured to our target environments, and polyfills only for features we actually use. During development, I test in multiple browsers at key milestones, and use BrowserStack or similar tools for devices I don't have physical access to. I also set up automated cross-browser testing for critical paths to catch regressions."

Mediocre Response: "I check caniuse.com to see which features are supported in which browsers. For CSS, I use autoprefixer to handle vendor prefixes, and for JavaScript, I use Babel to transpile to ES5 for older browsers. I test on Chrome, Firefox, and Safari during development, and if there are issues in IE or Edge, I'll add specific fixes for those browsers."

Poor Response: "I develop primarily in Chrome since that's what most users have, and then check Edge and Firefox before shipping. We use a modern build system that handles most compatibility issues automatically. If specific browsers have problems, I'll add CSS hacks or polyfills as needed to fix the major issues. For very old browsers, we usually just show a message asking users to upgrade."

6. What strategies do you use to create reusable UI components?

Great Response: "I design components with the single responsibility principle in mind, creating focused components that do one thing well. I implement a clear component API with explicit, well-documented props using TypeScript interfaces or PropTypes, including default values and validation. I separate business logic from presentation using container/presentational patterns or hooks, making components more portable across projects. I use composition over inheritance, designing smaller components that can be combined in various ways rather than creating monolithic ones. For styling, I implement theme-based design tokens rather than hardcoded values, allowing components to adapt to different visual contexts. I also ensure components are tested in isolation with both unit tests and visual regression tests. Finally, I document components comprehensively with usage examples, edge cases, accessibility considerations, and performance implications."

Mediocre Response: "I try to identify patterns in our UI and extract them into shared components. I make components configurable with props so they can be used in different contexts, and I use CSS modules or styled-components to keep the styles scoped to each component. I add these to our component library and document how to use them so other developers can find and reuse them."

Poor Response: "I look for UI elements that appear multiple times in our designs and turn those into components. I make sure they accept basic props for different variations, but if a new use case needs significant changes, I usually just copy the component and modify it rather than overcomplicating the original. This keeps things simpler and prevents breaking existing implementations."

7. How do you implement animations in your UI that enhance user experience without causing accessibility issues?

Great Response: "I approach animations with both purpose and restraint, ensuring they enhance rather than distract from the user experience. I follow the WCAG guidelines for animation, particularly the requirement to provide mechanisms to pause, stop, or hide any animation that auto-plays for more than 5 seconds. I respect user preferences by checking the prefers-reduced-motion media query and providing alternative non-animated or simplified transitions for users who enable this setting. For implementation, I focus on performance by prioritizing CSS animations and transitions over JavaScript when possible, especially for simple transitions. I animate properties that trigger only compositing in the browser rendering pipeline (like transform and opacity) to avoid layout thrashing. For complex animations, I use requestAnimationFrame properly or leverage libraries like GSAP that optimize performance. I also ensure animations serve clear purposes: providing feedback, showing relationships between elements, or guiding attention—never just for decoration."

Mediocre Response: "I use CSS transitions and animations for simple effects, and libraries like GSAP for more complex animations. I make sure to check the 'prefers-reduced-motion' media query to disable animations for users who don't want them. I try to keep animations subtle and purposeful, using them mainly for user feedback and transitions between states. I test animations to make sure they run smoothly without causing performance issues."

Poor Response: "I implement animations using CSS transitions for simple effects and JavaScript libraries for more complex ones. I keep animations relatively short so they don't slow down the user experience. If animations cause performance problems, I'll simplify them or remove them from mobile devices. Most modern devices can handle animations well, so performance isn't usually an issue unless you're doing something really complex."

8. How do you approach testing your UI code?

Great Response: "I implement a comprehensive testing strategy with multiple layers. At the unit level, I use Jest for testing individual functions and component logic, focusing on input/output relationships and edge cases. For component testing, I use React Testing Library or Vue Testing Library to test components in isolation, focusing on user interactions rather than implementation details. For integration testing, I write tests that verify multiple components work together correctly. I implement visual regression testing using tools like Percy or Chromatic to catch unexpected visual changes. For critical user flows, I set up end-to-end tests with Cypress or Playwright that simulate real user journeys. I also conduct accessibility testing with both automated tools like axe-core and manual testing with screen readers. Throughout development, I maintain a healthy testing pyramid with more unit tests than integration tests, and more integration tests than E2E tests, balancing coverage with maintenance costs."

Mediocre Response: "I write unit tests for utility functions and complex component logic using Jest. For components, I test that they render correctly with different props and simulate basic user interactions. I try to maintain good test coverage, but focus mainly on the critical paths. For larger features, we have some integration tests that check that components work together correctly. Before releasing, I manually test on different browsers to catch any visual or interaction issues."

Poor Response: "I focus on testing the core functionality manually across browsers. For automated testing, we have some unit tests for utility functions, but I find UI tests often break with minor design changes so they're not always worth the maintenance effort. When we implement new features, I create test plans to verify the critical paths work correctly. If bugs are found, I add specific tests for those cases to prevent regressions."

9. Explain how you would optimize the rendering performance of a component that displays a large dataset.

Great Response: "For large datasets, efficient rendering is crucial. I'd implement virtualization (or 'windowing') using libraries like react-window or react-virtualized to render only the visible items instead of the entire list. This significantly reduces DOM nodes and improves initial load and scroll performance. I'd implement pagination or infinite scrolling depending on the UX requirements, with proper loading states and error handling. To optimize further, I'd use memoization techniques like React.memo, useMemo, and useCallback to prevent unnecessary re-renders when data or props change. I'd also implement debouncing for user inputs that filter or sort the data to avoid excessive re-renders during typing. For very large datasets, I might implement worker threads for heavy calculations or sorting operations to keep the main thread responsive. Throughout implementation, I'd use the React Profiler and Chrome Performance tools to identify and address specific bottlenecks, measuring key metrics like Time to Interactive and frame rates during scrolling."

Mediocre Response: "I'd implement pagination to break the dataset into manageable chunks that load on demand, or use infinite scrolling if that's better for the UX. For React components, I'd use React.memo to prevent unnecessary re-renders, and make sure any filtering or sorting operations aren't running on every render. If performance is still an issue, I might look into virtualization libraries that only render the visible items in the viewport."

Poor Response: "I'd start by loading the data in chunks rather than all at once, using pagination controls so users can navigate through the dataset. If that's not enough, I'd simplify the UI of each list item to improve rendering speed and remove any complex calculations from the rendering process. If we really need to show a lot of data at once, I'd consider using a specialized data grid library that's optimized for handling large datasets."

10. How do you approach state management in complex applications?

Great Response: "I approach state management by first categorizing different types of state and choosing appropriate solutions for each. For UI state (like open/closed modals, active tabs), I keep it local to components using useState or useReducer in React. For shared state across components, I evaluate the complexity and scope—using React Context with proper memoization for simpler cases, or dedicated libraries like Redux, MobX, or Zustand when we need more robust features like middleware, time-travel debugging, or performance optimizations for complex state. I implement a clear architecture that separates state logic from UI components, using patterns like actions/reducers or state machines for predictable state transitions. For server data, I use specialized tools like React Query or SWR that handle caching, background updates, and synchronization. I also establish conventions for state normalization to avoid duplication and inconsistencies. Throughout the application, I enforce immutability either through conventions or libraries like Immer to prevent hard-to-track mutations, and I implement proper error handling and loading states for all asynchronous operations."

Mediocre Response: "For small to medium applications, I use React Context and hooks for state that needs to be shared between components. For larger applications, I'd implement Redux or a similar state management library, organizing the store by feature and using selectors to access specific parts of the state. I try to keep component state local when possible and only elevate state to the global store when it needs to be shared across different parts of the application."

Poor Response: "I generally use Redux for most projects since it's well-established and has good tooling. I create actions and reducers for different features and connect components to the parts of the store they need. For simpler projects, React's Context API might be enough. The important thing is to have a single source of truth for data that multiple components need to access."

11. Describe your approach to implementing dark mode or theming in a web application.

Great Response: "I implement theming using CSS custom properties (variables) as a foundation, defining a comprehensive token system for colors, spacing, typography, and other visual properties. I structure these tokens in layers—base tokens for raw values, semantic tokens that reference base tokens, and component tokens that reference semantic tokens—creating a flexible system that can adapt to multiple themes. For theme switching, I use a combination of data attributes on the root element and media queries for 'prefers-color-scheme', respecting user system preferences by default while allowing manual override. I implement proper state management to persist user theme preferences in localStorage or backend settings. For components, I ensure all styles reference theme tokens rather than hard-coded values, and I address edge cases like user-generated content and third-party components. I also ensure proper handling of images and media with appropriate contrast in each theme, using techniques like CSS filters where appropriate. Throughout implementation, I test color contrast in all themes to maintain accessibility compliance."

Mediocre Response: "I create a set of CSS variables for colors, borders, and other theme-specific properties, and define different values for each theme. I use a theme provider component or context to manage which theme is active and switch the variables accordingly. I store the user's preference in localStorage so it persists between visits, and also check the prefers-color-scheme media query to respect system preferences. For components, I make sure they all use these variables instead of hardcoded colors."

Poor Response: "I create separate CSS files or class-based overrides for each theme, with different color schemes defined for each. When the user switches themes, I toggle classes on the body element or load different stylesheets. For images, I might need different versions for dark and light modes. This approach is straightforward and doesn't require changing our existing CSS structure too much."

12. How do you handle form validation and error states in your UI?

Great Response: "I implement form validation as a multi-layered approach focusing on both UX and accessibility. I start with HTML native validation attributes like required, pattern, and type for basic constraints, providing a fallback experience. For more complex validation, I use libraries like Yup, Zod, or Joi to define schema-based validation rules that are reusable and testable. I implement real-time validation with appropriate debouncing to provide immediate feedback without overwhelming users, but delay validation until after the first interaction with each field to avoid premature error states. For error presentation, I ensure errors are associated with specific fields using aria-describedby, and implement both color and icon-based indicators so errors aren't conveyed by color alone. I also implement form-level validation for cross-field validations and display a summary of errors at form submission. For accessibility, I ensure screen readers announce errors when they occur and can navigate directly to the first field with an error. I also implement proper focus management after submission attempts, guiding users to fields needing attention."

Mediocre Response: "I use a combination of HTML validation attributes and JavaScript validation functions. I typically validate on blur and on form submission, showing error messages next to the relevant fields. I use a form library like Formik or React Hook Form to handle the state management and validation logic. For error states, I add appropriate CSS classes to highlight fields with errors and display clear error messages that explain how to fix the issue."

Poor Response: "I add validation functions that run when the form is submitted, checking each field against its requirements. If there are errors, I prevent submission and display error messages next to the problematic fields. For most projects, I use the built-in HTML validation when possible, and add custom JavaScript validation for more complex rules. Users can see all the errors at once after trying to submit."

13. What techniques do you use to improve the perceived performance of web applications?

Great Response: "I focus on creating the perception of speed even when actual operations may take time. I implement skeleton screens instead of generic loading spinners, providing content placeholders that match the layout of the expected content to reduce perceived wait time. I use optimistic UI updates for actions like form submissions, immediately showing the expected result while the backend request processes in the background, with proper error handling to revert if needed. For multi-step processes, I implement progressive loading, showing usable UI elements as soon as they're available rather than waiting for everything to load. I leverage prefetching and preloading strategically—prefetching likely navigation routes when the user hovers over links, and preloading critical resources during idle browser time. I also implement instant feedback for all user interactions, even if the actual operation takes time, ensuring buttons show active states immediately and interactive elements respond within 100ms. For longer operations, I use progress indicators with realistic timing rather than indeterminate spinners, as users perceive time passing more quickly when they can monitor progress."

Mediocre Response: "I use techniques like loading spinners and progress bars to let users know something is happening. I implement code splitting to reduce initial load times, and lazy load components and images that aren't immediately visible. For slow operations, I show immediate feedback like button state changes before starting the actual operation. I also use techniques like skeleton screens instead of blank loading states to make the loading experience feel faster."

Poor Response: "I make sure to show loading indicators whenever we're waiting for data, so users know the application is working. I try to optimize the actual performance through code splitting and image optimization so things load faster. For slow operations, I disable buttons while processing to prevent double-clicks and add loading states to sections that are being updated."

14. How do you handle cross-browser CSS inconsistencies?

Great Response: "I tackle cross-browser consistency through multiple complementary approaches. First, I establish a solid foundation using modern CSS reset libraries like normalize.css or sanitize.css, which provide consistent defaults while preserving useful browser defaults. I leverage PostCSS with plugins like autoprefixer configured with a precise browserslist to automatically handle vendor prefixes based on our supported browsers. For newer CSS features, I implement feature detection using @supports queries rather than browser detection, providing appropriate fallbacks that maintain core functionality. I organize CSS with a methodology like BEM or CUBE CSS to minimize cascade issues that often manifest differently across browsers. For layout, I use modern approaches like Flexbox and Grid with well-tested fallbacks for older browsers when necessary. Throughout development, I test on multiple browsers at key milestones, using both real devices and tools like BrowserStack for comprehensive coverage. I also document known browser-specific issues and solutions in our codebase, particularly for edge cases around form elements, font rendering, and scrolling behavior."

Mediocre Response: "I use a CSS reset or normalize.css to create a consistent baseline across browsers. I rely on autoprefixer to handle vendor prefixes automatically based on our browser support requirements. For layout issues, I test in major browsers and add specific fixes for browsers that have problems. I try to use well-supported CSS features when possible, and provide fallbacks for newer features using @supports or feature detection."

Poor Response: "I develop primarily in Chrome and then check for issues in other browsers before shipping. I use a CSS reset to minimize differences and add browser-specific CSS fixes when I find inconsistencies. For IE and older browsers, I sometimes need to add polyfills or specific hacks, but we're gradually dropping support for those. Most modern browsers have pretty good compatibility these days, so it's mainly just fixing small rendering differences."

15. How do you approach implementing a complex custom form component like a multi-step wizard or a dynamic form builder?

Great Response: "For complex form implementations, I start by breaking down the problem into manageable pieces and establishing a clear data architecture. For a multi-step form, I implement a state machine to manage transitions between steps, track completion status, and handle validation at both the step and form levels. I separate the data model from the UI components, creating a centralized store for form state that persists across steps. For navigation, I implement proper routing with history support so users can navigate with browser controls and bookmark specific steps. I build robust validation that validates the current step in real-time but also supports cross-field and cross-step validations. For accessibility, I ensure focus management between steps, implement proper landmark regions, and provide clear progress indicators that work for screen readers. I also implement data persistence (either local storage or backend saves) to prevent data loss if users leave and return. Throughout development, I test with realistic data volumes and edge cases, and implement comprehensive error handling both for validation errors and system errors like failed API calls."

Mediocre Response: "I use a state management solution to keep track of the form data across steps or configurations. For a multi-step form, I create a component for each step and a container component that manages which step is active and stores the complete form data. I implement validation at each step before allowing progression, and provide a way to review all inputs before final submission. For a dynamic form builder, I create reusable form components that can be configured and combined based on a schema or configuration object."

Poor Response: "I build separate components for each part of the form and use state to track which section is currently active. I store all the form data in a single state object that gets updated as the user progresses. For validation, I check each field when the user tries to move to the next step. It's important to keep the UI simple and guide users through the process step by step to avoid overwhelming them."

16. Explain your approach to implementing internationalization (i18n) in a web application.

Great Response: "I implement internationalization as a core architectural concern rather than an afterthought. I separate all user-facing strings into translation files organized by language and namespace/feature, using a robust i18n library like i18next or FormatJS that supports pluralization, date/number formatting, and context-based translations. I design components with text expansion/contraction in mind, avoiding fixed-width containers that might break in languages that take more space than English. For RTL language support, I use logical CSS properties (start/end instead of left/right) and test thoroughly in RTL mode. I implement proper locale detection that respects both browser settings and user preferences, with locale data stored in user profiles if applicable. For date, time, and number formatting, I use the Intl API with appropriate locale parameters rather than custom formatting logic. I also consider cultural differences beyond just language, such as name formats, address formats, and culturally appropriate imagery. Throughout development, I provide context and notes for translators in the translation files, and implement a workflow that allows for continuous translation updates without requiring code changes."

Mediocre Response: "I use an i18n library like i18next or react-intl to manage translations. I extract all user-facing text into translation files for each supported language, and use the library's components or functions to insert the appropriate translations based on the user's selected language. I make sure to handle pluralization rules and date/number formatting according to locale conventions. For the UI, I design with text expansion in mind, allowing components to grow as needed for longer text in other languages."

Poor Response: "I create JSON files with key-value pairs for each language we support, with the keys being identifiers and the values being the translated text. I then use these files to look up the correct text based on the user's language setting. For dates and numbers, I use library functions that handle different formats. I test the UI with translations to make sure everything still fits and looks good."

17. How do you optimize images for web performance while maintaining visual quality?

Great Response: "I implement a comprehensive image optimization strategy that balances quality, performance, and user experience. I select appropriate image formats based on content type—using WebP with JPEG/PNG fallbacks for photos, SVG for icons and illustrations, and AVIF for projects where cutting-edge performance is prioritized. I implement responsive images using the srcset and sizes attributes, providing multiple resolutions and allowing browsers to select the appropriate image based on device capabilities and viewport size. For art direction needs, I use the picture element with media queries to deliver different crops or compositions at different breakpoints. I apply appropriate compression levels based on image content and importance, using tools like Sharp, ImageMagick, or specialized services like Cloudinary as part of the build process. I implement lazy loading for images below the fold using loading='lazy' or Intersection Observer for older browsers. For critical above-the-fold images, I consider techniques like LQIP (Low Quality Image Placeholders) to improve perceived performance. Throughout implementation, I ensure proper alt text for accessibility and implement width and height attributes to reserve space during loading to prevent layout shifts."

Mediocre Response: "I compress images using tools like ImageOptim or TinyPNG before adding them to the project. I use modern formats like WebP with appropriate fallbacks for older browsers, and implement responsive images using srcset and sizes attributes to deliver different sized images based on screen size. I apply lazy loading to images that aren't immediately visible on page load. For vector graphics, I use SVGs and optimize them by removing unnecessary metadata."

Poor Response: "I resize images to the maximum size they'll be displayed at and run them through compression tools to reduce file size. I use JPEG for photos and PNG for graphics with transparency. For responsive design, I usually create a few different sizes of each image and load the appropriate one based on screen size. Most modern image compression tools do a good job of balancing quality and file size automatically."

18. How do you handle error states and edge cases in your UI components?

Great Response: "I implement a systematic approach to error handling across the application. I categorize errors into different types—network failures, validation errors, authentication issues, server errors, etc.—and design appropriate UI patterns for each. I implement graceful degradation, ensuring components fail safely without breaking the entire application, using error boundaries in React or similar patterns in other frameworks. For asynchronous operations, I implement comprehensive loading, success, and error states with appropriate retry mechanisms where applicable. I ensure error messages are human-readable and actionable, providing clear next steps for users rather than technical details. For edge cases, I use explicit null/empty states rather than allowing components to break or display partially, designing these states to guide users toward successful interactions. I also implement proper logging and monitoring to capture errors that reach production, allowing us to prioritize fixes based on frequency and impact. Throughout development, I test error paths as thoroughly as success paths, including simulated network failures, malformed data, and boundary conditions."

Mediocre Response: "I design explicit states for each component, including loading, error, empty, and success states. For error handling, I implement try-catch blocks around operations that might fail and display appropriate error messages to users. I try to anticipate edge cases like empty data sets, extremely long content, or slow network conditions, and design the UI to handle these gracefully. I use error boundaries in React to prevent the entire application from crashing when a component fails."

Poor Response: "I add error handling for the main failure points in the application, like API calls and form submissions. When errors occur, I show an error message to the user explaining what went wrong. For edge cases like empty states, I display placeholder content or messages. I test the main user flows to make sure they work correctly, and fix any issues that come up during testing."

19. Describe your approach to implementing a design system in a web application.

Great Response: "I approach design systems as living documentation that bridges design and development workflows. I start by auditing existing UI elements and establishing core design tokens for colors, typography, spacing, shadows, and other fundamental properties, implementing them as CSS custom properties or in a format appropriate for the tech stack. I build a component library in layers—starting with primitives like buttons and inputs, then composing them into more complex patterns like forms and cards. I implement components using an API-first approach, thoroughly documenting props, variants, and composition patterns. For maintainability, I create a clear governance model defining how components are added, modified, or deprecated, with explicit versioning to manage changes. I implement comprehensive testing including unit tests, visual regression tests, and accessibility tests to ensure quality. For documentation, I use tools like Storybook to create living documentation with interactive examples, usage guidelines, and implementation details. Throughout development, I ensure the system is adopted by fostering collaboration between designers and developers, creating tooling for both audiences, and measuring usage to identify gaps or opportunities for improvement."

Mediocre Response: "I start by defining design tokens for colors, typography, spacing, and other visual elements, and implement them as variables in our CSS system. I create reusable components for common UI elements, documenting their props and usage patterns. I use Storybook or a similar tool to showcase these components and provide examples. I work with designers to ensure the component implementations match the design specifications, and establish processes for adding new components or modifying existing ones."

Poor Response: "I create a shared component library with the most commonly used UI elements like buttons, inputs, and cards. I implement consistent styles using a CSS framework or custom styles, making sure all components look and behave consistently. I document how to use each component so other developers can implement them correctly. When designs change, I update the components in the library so everyone gets the changes automatically."

20. How do you approach implementing complex animations or transitions in a UI?

Great Response: "I approach complex animations methodically, starting with a clear purpose for each animation that enhances user experience rather than distracting from it. I begin by creating storyboards or low-fidelity prototypes to validate animation concepts with stakeholders before implementation. For implementation, I select the appropriate technology based on animation complexity—using CSS transitions/animations for simple state changes, CSS keyframes for more complex sequences, and JavaScript libraries like GSAP or Framer Motion for advanced physics-based or coordinated animations. I implement animations with performance in mind, focusing on properties that only trigger compositing (transform, opacity) rather than those that cause layout recalculations. I organize complex animations using the FLIP technique (First, Last, Invert, Play) when appropriate to maintain 60fps even during significant layout changes. For accessibility, I respect 'prefers-reduced-motion' settings and provide alternative, simplified transitions. I also ensure animations have appropriate timing—quick enough to feel responsive but slow enough to be perceived (typically 200-500ms for UI transitions). Throughout development, I test animations on both high and low-end devices to ensure consistent performance, and use Chrome DevTools Performance panel to identify and fix any frame rate issues."

Mediocre Response: "I start by defining the purpose of the animation and creating simple prototypes to test the concept. For implementation, I use CSS animations and transitions for simpler effects, and libraries like GSAP or Framer Motion for more complex sequences. I make sure to animate properties that perform well (transform and opacity) and avoid properties that trigger reflows. I implement the 'prefers-reduced-motion' media query to respect user preferences, and test the animations across different devices to ensure they run smoothly."

Poor Response: "I usually start by looking at similar animations online to get ideas, then implement them using CSS transitions for simple effects or JavaScript libraries for more complex ones. I make sure the animations aren't too slow or distracting, and test them on different browsers to make sure they work everywhere. If performance is an issue on mobile devices, I'll simplify the animations or disable some of them."