I started with the scroll listener approach and it felt fine until they asked how I'd prevent firing 40 requests per second while someone drags the scrollbar.
Start by clarifying requirements and constraints, then outline a component architecture that separates data fetching, state management, and rendering. Discuss trade-offs between scroll-based and button-based loading, and cover edge cases like error handling, caching, and performance.
Pro tip: Mention that you would debounce scroll events and use Intersection Observer for performance, and that you'd implement request cancellation to avoid race conditions when the component unmounts or the user navigates away.
Ask about expected data volume, error handling needs, whether infinite scroll or load more button is preferred, and if there are any accessibility or SEO considerations.
Propose a component structure with a container managing state (items, page, loading, error) and a presentational list. Consider using hooks like useReducer for complex state.
Describe how to fetch paginated data in batches of 10, append results, and handle loading states. Mention using AbortController to cancel in-flight requests on unmount.
Explain how to detect when to load more: either via a button click or by using Intersection Observer on a sentinel element at the end of the list, with debouncing for scroll events.
Discuss error handling with retry, empty states, caching fetched pages, and performance optimizations like memoization and virtualization for large lists.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Covered loading spinners and disabling the trigger while a request is in flight.
Start by clarifying the component's data-fetching pattern (e.g., infinite scroll, pagination) and the expected user experience. Then walk through a state machine covering loading, success, empty, end-of-list, and error states, and explain how you'd implement retry with exponential backoff and idempotency. Emphasize trade-offs like optimistic updates vs. conservative loading, and how you'd test edge cases.
Pro tip: Mention that you'd avoid duplicate requests by using a request ID or cancellation token, and that you'd persist retry attempts in a ref or state to prevent infinite loops. Also, highlight that you'd surface a 'Retry' button only after automatic retries fail, to balance UX and server load.
Ask about the data source (REST, GraphQL), pagination style (cursor vs. offset), and expected network conditions. Confirm if the component needs to support offline mode or optimistic updates.
Outline states: idle, loading (initial and more), success, empty, end-of-list, and error. Describe how you'd show a spinner for initial load, a footer loader for more, and a subtle 'no more items' message.
Explain using the API response (e.g., nextCursor null or hasMore flag) and/or an IntersectionObserver on a sentinel element. Mention debouncing to avoid multiple triggers.
Describe automatic retries with exponential backoff and jitter, capped at a few attempts. Then show a manual retry button that resets the error state and re-fetches only the failed page.
Compare optimistic vs. pessimistic updates, and how retries affect UX and server load. Mention unit tests for state transitions and integration tests with mocked network failures.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by explaining the problem: scroll events fire rapidly and can trigger many API calls, so we need to limit calls and avoid duplicates. Then describe a debounce implementation (e.g., using setTimeout) and a request deduplication strategy (e.g., caching in-flight promises). Finally, discuss trade-offs and edge cases like cancellation and error handling.
Pro tip: Mention that you'd use a leading-edge debounce or throttle for immediate feedback, and that you'd store in-flight promises in a Map keyed by request parameters to deduplicate. Also, consider using AbortController to cancel stale requests.
Ask about the expected frequency of scroll events, the API's rate limits, and whether immediate feedback is needed. This shows you consider the context before coding.
Explain how to use setTimeout to delay the API call until scrolling pauses, and clear the timeout on each new event. Mention options like leading/trailing edges and throttle as an alternative.
Describe using a Map to store promises keyed by a unique request identifier (e.g., URL + params). When a new request comes in, check if an identical one is already in-flight and reuse its promise.
Discuss using AbortController to cancel previous requests when a new one is triggered, and removing entries from the Map once promises settle to avoid memory leaks.
Talk about latency vs. freshness, error handling, and how this scales. Mention that debouncing may delay critical updates, so consider a hybrid approach with throttling.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.