Combining Virtualization with Data Fetching

Infinite scroll loads more data as the user nears the end of the list, instead of paginating with explicit page buttons. Combined with virtualization, it lets you browse huge datasets fluidly.

The list shows only visible rows while new data is fetched in the background just before the user reaches the bottom.

react-window list components accept an onItemsRendered callback that reports which item indices are currently rendered. It provides visible and overscan start and stop indices.

This callback is your hook into scrolling, letting you detect how far through the list the user has scrolled without wiring up raw scroll events.

To know when to fetch, compare the overscanStopIndex from onItemsRendered against the current itemCount. When the rendered window approaches the end of the loaded data, more is needed.

Using the overscan stop index gives a little lead time, triggering the fetch slightly before the user actually hits the very last row.

When the stop index crosses a threshold, say within a screenful of itemCount, you call your fetch function for the next page. Guard it so you do not fire multiple overlapping requests.

A loading flag or checking whether a fetch is already in flight prevents duplicate requests as the user scrolls through the trigger zone.

A clean trick is to render itemCount as the loaded count plus one while more data exists. The extra row renders a spinner, signaling that fetching is underway.

Once new data arrives, the count grows and the spinner row is replaced by real content, giving smooth visual feedback.

The react-window-infinite-loader companion package wraps this logic for you. You provide isItemLoaded, loadMoreItems, and itemCount, and it calls your loader as the user scrolls toward unloaded rows.

It handles the bookkeeping of which ranges are loaded and prevents redundant load calls, simplifying robust infinite scroll.

For unloaded indices you can render placeholder or skeleton rows instead of blanks. The render function checks whether the item at an index is loaded and shows a skeleton if not.

Skeletons preserve layout and communicate progress, which feels better than empty space while the next page is on its way.

Fetches can fail, so handle errors gracefully. You can render a special error row at the end with a retry button that re-invokes the load function for the failed range.

This keeps the list usable after a hiccup and gives the user a clear way to recover without reloading the whole page.

Two common pagination styles feed infinite lists. Offset pagination requests by page number or skip count, while cursor pagination requests items after an opaque cursor pointing at the last seen item.

Cursor pagination is generally more reliable for live, changing data because it avoids the shifting and duplication that offsets can cause when items are inserted.

React Query useInfiniteQuery pairs naturally with virtualization. It manages fetched pages, the next cursor, and loading and error states, while react-window renders the flattened pages efficiently.

You flatten the pages into a single array for the list and call fetchNextPage from your onItemsRendered threshold, getting caching and retries for free.

Identify when to fetch more data in a virtualized infinite list.

Infinite scroll loads pages as the user nears the end. onItemsRendered reports indices, and comparing overscanStopIndex to itemCount tells you when to fetch, guarded against duplicate requests.

Use placeholder and error rows, react-window-infinite-loader for bookkeeping, and cursor pagination for live data. React Query useInfiniteQuery manages pages, cursors, and states alongside react-window rendering.