React Virtuoso

react-virtuoso

react-virtuoso renders only the visible portion of large lists, grids, and tables. It measures item sizes automatically with ResizeObserver — variable item heights work out of the box, with no size configuration.

import { Virtuoso } from 'react-virtuoso'
;<Virtuoso style={{ height: '100%' }} data={users} itemContent={(index, user) => <div>{user.name}</div>} />

Picking the right component

All components share the same core props (data/totalCount, itemContent, components, scroll callbacks, ref methods).

What you do NOT need to do

Unlike TanStack Virtual or react-window, react-virtuoso measures items itself. Do not carry those libraries' patterns over:

• No estimateSize, no measureElement, no data-index wiring — measurement is automatic.
• No absolute positioning or transform: translateY on items — the library positions items.
• No fixed itemSize requirement — variable heights are the default. If items genuinely have one uniform height, pass fixedItemHeight as a performance optimization only.
• No windowing math — pass data (or totalCount) and render the item in itemContent.

Core rules

• The component needs a height. Set style={{ height: '100%' }} (with a sized parent) or a fixed height. A zero-height container renders nothing.
• Never put CSS margins on items. ResizeObserver reports contentRect, which excludes margins, so the computed total height comes up short — the classic symptom is a list that cannot scroll all the way to the bottom. Use padding instead. Watch for default margins on <p>, headings, <ul>, <blockquote>, <pre>.
• Use data, not totalCount, when you have the items. With data, itemContent={(index, item) => ...} receives the item. Use totalCount only when items are derived from the index. Updates must produce a new array reference.
• Provide computeItemKey={(index, item) => item.id} whenever the list can be prepended, reordered, or filtered. The default key is the index, which remounts items (losing state) when positions shift.
• Define components overrides outside the render function. Inline definitions create a new component type each render, remounting the subtree on every scroll. Scroller and List overrides must forward ref to their DOM element.
• Item content must not render zero-height elements. The error "zero-sized element, this should not happen" means an item measured 0px — filter empty items out of the data instead.

Common patterns

Infinite scrolling

<Virtuoso data={items} endReached={() => loadMore()} itemContent={(index, item) => <Item item={item} />} />

endReached fires at the bottom; render a spinner via components.Footer. For "load more" on click, put the button in Footer.

Prepending items (reverse infinite scroll)

Prepending naively makes the list jump. Instead, keep a firstItemIndex that you decrease by the number of prepended items:

const [firstItemIndex, setFirstItemIndex] = useState(START)

const prepend = async () => {
  const older = await fetchOlderItems()
  setFirstItemIndex((i) => i - older.length)
  setItems((current) => [...older, ...current])
}

<Virtuoso
  computeItemKey={(_, item) => item.id}
  data={items}
  firstItemIndex={firstItemIndex}
  initialTopMostItemIndex={{ index: 'LAST' }}
  startReached={() => void prepend()}
  ...
/>

firstItemIndex must stay a positive number, so start it large (e.g. 100000). For GroupedVirtuoso, decrease it by the number of new items only, excluding the group headers. See endless-scrolling.

Following new items (logs, feeds)

<Virtuoso followOutput="smooth" data={messages} ... />

followOutput scrolls to new bottom items only when the user is already at the bottom. It accepts 'auto' | 'smooth' | false or a function (isAtBottom) => ... for custom logic. For full chat UIs prefer @virtuoso.dev/message-list.

Scrolling programmatically

const ref = useRef<VirtuosoHandle>(null)
ref.current?.scrollToIndex({ index: 500, align: 'center', behavior: 'smooth' })

Also on the handle: scrollIntoView (only scrolls if not visible — right for keyboard navigation), scrollTo/scrollBy (pixel-based), and getState (snapshot for restoreStateFrom when remounting, e.g. back navigation).

To start at an item, use initialTopMostItemIndex={{ index, align: 'start' }} — not initialScrollTop, which first renders at the top and then jumps.

Grouped lists

<GroupedVirtuoso
  groupCounts={[20, 30]} // items per group, in order
  groupContent={(groupIndex) => <Header group={groups[groupIndex]} />}
  itemContent={(index, groupIndex) => <Item item={items[index]} />} // index is absolute across all items
/>

You provide flat data plus groupCounts; map indexes back to your data yourself.

Tables

<TableVirtuoso
  data={rows}
  fixedHeaderContent={() => (
    <tr>
      <th>Name</th>
    </tr>
  )}
  itemContent={(index, row) => (
    <>
      <td>{row.name}</td>
    </>
  )} // <td> cells only — the row <tr> is rendered for you
/>

Do not set border-collapse: collapse on the table — the sticky header's borders scroll away with the body. Use border-collapse: separate with explicit cell borders. Customize structure via components (Table, TableRow, TableHead, TableBody).

Grid

VirtuosoGrid virtualizes same-sized items in columns. You control column count with CSS — give components.Item a percentage width (33% for three columns, changed via media queries) and components.List display: flex; flex-wrap: wrap. See grid-responsive-columns.

Page-level scrolling

Use useWindowScroll to drive the list from the document scroll, or customScrollParent={element} to attach to an existing scrollable ancestor. Pick exactly one scroll mode — combining them makes both containers scroll.

Testing

JSDOM has no layout, so items will not render in Jest/Vitest without mocked measurements:

render(<Virtuoso data={data} />, {
  wrapper: ({ children }) => (
    <VirtuosoMockContext.Provider value={{ viewportHeight: 300, itemHeight: 100 }}>{children}</VirtuosoMockContext.Provider>
  ),
})

Use VirtuosoGridMockContext (adds viewportWidth, itemWidth) for grids. Prefer real-browser tests (Playwright) for scroll behavior.

Troubleshooting

Tuning: increaseViewportBy renders extra pixels outside the viewport (smoother, more DOM); defaultItemHeight skips the initial probe render; fixedItemHeight skips measurement entirely (uniform items only); scrollSeekConfiguration swaps items for placeholders during fast scrolling.

References

Detailed guides with full code in references/:

• references/README.md — package overview and full feature list
• references/1.virtuoso/ — flat list guides: basic-usage, endless-scrolling, press-to-load-more, initial-index, scroll-to-index, keyboard-navigation, customize-rendering, footer, top-items, scroll-handling, range-change-callback, scroll-seek-placeholders, auto-resizing, window-scrolling, custom-scroll-container, horizontal-mode
• references/2.grouped-virtuoso/ — grouped lists: grouped-numbers, grouped-by-first-letter, scroll-to-group, grouped-with-load-on-demand
• references/3.virtuoso-grid/ — grid-responsive-columns
• references/4.table-virtuoso/ — tables: basic-table, table-fixed-headers, table-fixed-columns, table-grouped
• references/5.third-party-integration/ — mocking-in-tests, tanstack-table-integration, mui-table-virtual-scroll, material-ui-endless-scrolling
• references/6.troubleshooting.md — full troubleshooting guide

Full API reference: https://virtuoso.dev/react-virtuoso/