The double underscore thing is easy to miss if you're not already writing BEM.
Start by clarifying the requirements: the list is rendered from an in-memory array, and CSS class names must follow BEM with double underscores (e.g., list__item). Then outline a component-based solution that maps over the array to render items, ensuring each item has the correct class name, and discuss how you would handle dynamic updates or performance considerations.
Pro tip: Mention that you would write a quick test or use a linter to enforce the double underscore convention, showing attention to detail and proactive quality assurance. Also, briefly note that BEM naming improves maintainability and avoids style conflicts, which is crucial in large codebases like TikTok's.
Confirm that the list is rendered from an in-memory array, and that CSS class names must use double underscores (BEM-style). Ask if there are any other constraints like performance or accessibility.
Decide between a simple map over the array or a more optimized solution (e.g., virtualized list) based on the expected size. For an in-memory array, a straightforward map is usually sufficient.
Create a component that iterates over the array and renders each item with the correct BEM class name (e.g., `list__item`). Ensure the container has a class like `list`.
Discuss how the component would handle changes to the array (e.g., adding/removing items) and edge cases like empty lists or duplicate keys.
Mention writing unit tests to verify that the correct class names are applied and that the list renders as expected. Consider using a linter or stylelint to enforce BEM naming.
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Start by clarifying requirements and assumptions, then outline a component-based solution with controlled form state, error handling, and optimistic UI updates. Emphasize preserving user input on failure and clearing on success, and discuss trade-offs like optimistic vs pessimistic updates and accessibility.
Pro tip: Demonstrate maturity by mentioning that you would use a form library like React Hook Form to manage state and validation, and that you would debounce submissions to prevent duplicate requests. Also, highlight the importance of accessible error messages with aria-live regions.
Ask about the tech stack, API contract, and expected UX. Confirm that the 400 error is simulated and that the form should be cleared only on success.
Propose a controlled form component with local state for input value, error message, and submission status. Use a form library or custom hooks for validation and submission.
On submit, send a POST request. On success, append the new item to the list and reset the form. On failure (400), keep the input value and display a validation message.
Disable the submit button during submission, show loading indicators, and ensure error messages are accessible. Consider optimistic updates for better UX.
Talk about trade-offs between optimistic and pessimistic updates, and how you would test the component with unit and integration tests.
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The deduplication part is what tripped me up.
Start by outlining the component's state machine (loading, success, error) and how you'll fetch data with proper cleanup. Then explain your rendering logic, emphasizing how you merge server data with local items using unique IDs to prevent duplicates. Finally, discuss edge cases like race conditions and optimistic updates.
Pro tip: Mention using a stable unique identifier (like a UUID) for locally added items and a merge strategy that deduplicates by ID, rather than relying on array position or deep equality. This shows you understand real-world data synchronization challenges.
Identify the states: loading, success, error, and possibly refreshing. Plan how to trigger the fetch (e.g., useEffect) and handle cleanup to avoid memory leaks.
Describe the API call, including error handling and loading indicators. Mention using async/await or promises with try/catch.
Explain conditional rendering: show spinner during loading, error message on failure, and the list on success. Ensure the UI is responsive and accessible.
Detail how to combine locally added items with server data without duplicates. Use unique IDs and a merge function that prioritizes local items or updates them if they exist on the server.
Discuss race conditions (e.g., multiple fetches), optimistic updates, and how to handle server-side changes to locally added items.
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This felt like five questions crammed into one.
Structure your answer around a real or hypothetical component you've built, walking through each concern in a logical order from structure to testing. Emphasize trade-offs and how you balance accessibility, performance, and maintainability. Conclude with how you'd test each aspect to ensure reliability.
Pro tip: Tie each point back to user impact and business value—e.g., accessibility improves SEO and broadens audience, idempotent updates prevent duplicate charges. This shows you think beyond code.
Start by describing how you organize files and components for clarity and reuse. Then explain how you ensure accessibility with proper labels, button types, and ARIA attributes where needed.
Discuss your approach to managing state locally and globally, and how you avoid unnecessary re-renders using memoization, selectors, or immutable updates.
Explain how you design update operations to be idempotent (e.g., using unique IDs, debouncing, or server-side checks) and how you handle events efficiently with delegation or synthetic events.
Describe your error handling patterns (error boundaries, try-catch, user feedback) and how you test each layer: unit tests for logic, integration tests for interactions, and E2E tests for critical flows.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.