## Problem A home feed can have thousands of posts. Rendering all DOM nodes at once causes severe performance problems. Implement a virtualized list that only renders the posts currently visible in the viewport, plus a small buffer above and below. ```js class VirtualizedFeed { constructor(container, items, itemHeight) { // container: HTMLElement // items: array of data objects // itemHeight: fixed height per item in px } render() { ... } // initial render onScroll() { ... } // called on scroll event; updates visible window updateItems(newItems) { ... } // append or prepend new items } ``` **Requirements:** Only N visible items + 5 buffer items above and below are in the DOM at any time. Scroll position must feel native. ## Follow-ups 1. How do you calculate which item indices are visible given scrollTop and containerHeight? 2. How do you maintain scroll position when prepending new items (e.g., "5 new posts") at the top? 3. How do variable-height items change the virtualization math? 4. How would you handle keyboard navigation (arrow keys) through the virtualized list?

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Home Feed Scroll: Implement Virtualized Rendering for a High-Volume Home Feed

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Problem A home feed can have thousands of posts. Rendering all DOM nodes at once causes severe performance problems. Implement a virtualized list that only renders the posts currently visible in the viewport, plus a small buffer above and below. Requirements: Only N visible items + 5 buffer items above and below are in the DOM at any time. Scroll position must feel native. Follow-ups How do you calculate which item indices are visible given scrollTop and containerHeight? How do you maintain scro…

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It covers the following topics: Frontend, Phone, Coding, Arrays, Onsite .

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Home Feed Scroll: Implement Virtualized Rendering for a High-Volume Home Feed

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