Imagine a page with many cards and lazy loading (like on Stripchat). What corner cases do you see, what problems might arise, and what would you optimize? How does virtualization (React Window) work?

When implementing a page with many cards and lazy loading, the following corner cases and issues may arise:

• Performance issues: rendering all cards at once can cause the page to slow down.
• Positioning issues: dynamically adding cards may disrupt scrolling or cause content to jump.
• Data loading issues: errors during loading, retries, and loading states need to be handled correctly.
• Unique key issues: React requires unique keys for list items.
• SEO issues: lazy loading can make content indexing difficult.

To optimize, virtualization can be used — rendering only visible cards and a small buffer around them in the DOM. This significantly reduces browser load.

How virtualization (React Window) works:

React Window renders only the list items visible in the current viewport, plus a small buffer above and below. It calculates item sizes and positions them using absolute positioning within a container with fixed height and overflow: auto. When scrolling, React Window updates the displayed set of items, allowing large lists to be handled efficiently.

Example of using React Window:

import { FixedSizeList as List } from 'react-window';

const Row = ({ index, style }) => (
  <div style={style}>Card #{index}</div>
);

<List
  height={500}
  itemCount={1000}
  itemSize={50}
  width={300}
>
  {Row}
</List>

This renders only visible rows, saving resources.