tanstack-virtual— agent skill

Overview

TanStack Virtual provides virtualization logic for rendering only visible items in large lists, grids, and tables. It calculates which items are in the viewport and positions them with absolute positioning, keeping DOM node count minimal regardless of dataset size.

Package: @tanstack/react-virtual Core: @tanstack/virtual-core (framework-agnostic)

Installation

npm install @tanstack/react-virtual

Core Pattern

import { useVirtualizer } from '@tanstack/react-virtual'

function VirtualList() {
  const parentRef = useRef<HTMLDivElement>(null)

  const virtualizer = useVirtualizer({
    count: 10000,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 35, // estimated row height in px
    overscan: 5,
  })

  return (
    <div ref={parentRef} style={{ height: '400px', overflow: 'auto' }}>
      <div
        style={{
          height: `${virtualizer.getTotalSize()}px`,
          width: '100%',
          position: 'relative',
        }}
      >
        {virtualizer.getVirtualItems().map((virtualItem) => (
          <div
            key={virtualItem.key}
            style={{
              position: 'absolute',
              top: 0,
              left: 0,
              width: '100%',
              height: `${virtualItem.size}px`,
              transform: `translateY(${virtualItem.start}px)`,
            }}
          >
            Row {virtualItem.index}
          </div>
        ))}
      </div>
    </div>
  )
}

Virtualizer Options

Required

Optional

Virtualizer API

// Get visible items
virtualizer.getVirtualItems(): VirtualItem[]

// Get total scrollable size
virtualizer.getTotalSize(): number

// Scroll to specific index
virtualizer.scrollToIndex(index, { align: 'start' | 'center' | 'end' | 'auto', behavior: 'auto' | 'smooth' })

// Scroll to offset
virtualizer.scrollToOffset(offset, options)

// Force recalculation
virtualizer.measure()

VirtualItem Properties

interface VirtualItem {
  key: Key           // Unique key
  index: number      // Index in source data
  start: number      // Pixel offset (use for transform)
  end: number        // End pixel offset
  size: number       // Item dimension
  lane: number       // Lane index (multi-column)
}

Dynamic/Variable Heights

Use measureElement ref for items with unknown heights:

const virtualizer = useVirtualizer({
  count: items.length,
  getScrollElement: () => parentRef.current,
  estimateSize: () => 50, // overestimate
})

{virtualizer.getVirtualItems().map((virtualItem) => (
  <div
    key={virtualItem.key}
    data-index={virtualItem.index}  // REQUIRED for measurement
    ref={virtualizer.measureElement} // Attach for dynamic measurement
    style={{
      position: 'absolute',
      top: 0,
      left: 0,
      width: '100%',
      transform: `translateY(${virtualItem.start}px)`,
      // Do NOT set fixed height - let content determine it
    }}
  >
    {items[virtualItem.index].content}
  </div>
))}

Horizontal Virtualization

const virtualizer = useVirtualizer({
  count: columns.length,
  getScrollElement: () => parentRef.current,
  estimateSize: () => 100,
  horizontal: true,
})

// Use width for container, translateX for positioning
<div style={{ width: `${virtualizer.getTotalSize()}px`, position: 'relative' }}>
  {virtualizer.getVirtualItems().map((item) => (
    <div style={{
      position: 'absolute',
      height: '100%',
      width: `${item.size}px`,
      transform: `translateX(${item.start}px)`,
    }}>
      Column {item.index}
    </div>
  ))}
</div>

Grid Virtualization (Two Virtualizers)

function VirtualGrid() {
  const parentRef = useRef<HTMLDivElement>(null)

  const rowVirtualizer = useVirtualizer({
    count: 10000,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 35,
    overscan: 5,
  })

  const columnVirtualizer = useVirtualizer({
    count: 10000,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 100,
    horizontal: true,
    overscan: 5,
  })

  return (
    <div ref={parentRef} style={{ height: '500px', width: '500px', overflow: 'auto' }}>
      <div style={{
        height: `${rowVirtualizer.getTotalSize()}px`,
        width: `${columnVirtualizer.getTotalSize()}px`,
        position: 'relative',
      }}>
        {rowVirtualizer.getVirtualItems().map((virtualRow) => (
          <Fragment key={virtualRow.key}>
            {columnVirtualizer.getVirtualItems().map((virtualColumn) => (
              <div
                key={virtualColumn.key}
                style={{
                  position: 'absolute',
                  width: `${virtualColumn.size}px`,
                  height: `${virtualRow.size}px`,
                  transform: `translateX(${virtualColumn.start}px) translateY(${virtualRow.start}px)`,
                }}
              >
                Cell {virtualRow.index},{virtualColumn.index}
              </div>
            ))}
          </Fragment>
        ))}
      </div>
    </div>
  )
}

Window Scrolling

import { useWindowVirtualizer } from '@tanstack/react-virtual'

function WindowList() {
  const listRef = useRef<HTMLDivElement>(null)

  const virtualizer = useWindowVirtualizer({
    count: 10000,
    estimateSize: () => 45,
    overscan: 5,
    scrollMargin: listRef.current?.offsetTop ?? 0,
  })

  return (
    <div ref={listRef}>
      <div style={{
        height: `${virtualizer.getTotalSize()}px`,
        position: 'relative',
      }}>
        {virtualizer.getVirtualItems().map((item) => (
          <div
            key={item.key}
            style={{
              position: 'absolute',
              height: `${item.size}px`,
              transform: `translateY(${item.start - virtualizer.options.scrollMargin}px)`,
            }}
          >
            Row {item.index}
          </div>
        ))}
      </div>
    </div>
  )
}

Infinite Scrolling

import { useVirtualizer } from '@tanstack/react-virtual'
import { useInfiniteQuery } from '@tanstack/react-query'

function InfiniteList() {
  const { data, fetchNextPage, hasNextPage, isFetchingNextPage } = useInfiniteQuery({
    queryKey: ['items'],
    queryFn: ({ pageParam = 0 }) => fetchItems(pageParam),
    getNextPageParam: (lastPage) => lastPage.nextCursor,
  })

  const allItems = data?.pages.flatMap((page) => page.items) ?? []

  const virtualizer = useVirtualizer({
    count: hasNextPage ? allItems.length + 1 : allItems.length,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 50,
    overscan: 5,
  })

  useEffect(() => {
    const items = virtualizer.getVirtualItems()
    const lastItem = items[items.length - 1]
    if (lastItem && lastItem.index >= allItems.length - 1 && hasNextPage && !isFetchingNextPage) {
      fetchNextPage()
    }
  }, [virtualizer.getVirtualItems(), hasNextPage, isFetchingNextPage, allItems.length])

  // Render virtual items, show loader row for last item if loading
}

Sticky Items

import { defaultRangeExtractor, Range } from '@tanstack/react-virtual'

const stickyIndexes = [0, 10, 20, 30] // Header indices

const virtualizer = useVirtualizer({
  count: 1000,
  getScrollElement: () => parentRef.current,
  estimateSize: () => 50,
  rangeExtractor: useCallback((range: Range) => {
    const next = new Set([...stickyIndexes, ...defaultRangeExtractor(range)])
    return [...next].sort((a, b) => a - b)
  }, [stickyIndexes]),
})

// Render sticky items with position: sticky; top: 0; zIndex: 1

Smooth Scrolling

const virtualizer = useVirtualizer({
  scrollToFn: (offset, { behavior }, instance) => {
    if (behavior === 'smooth') {
      // Custom easing animation
      instance.scrollElement?.scrollTo({ top: offset, behavior: 'smooth' })
    } else {
      instance.scrollElement?.scrollTo({ top: offset })
    }
  },
})

// Usage
virtualizer.scrollToIndex(500, { align: 'center', behavior: 'smooth' })

Best Practices

1. Overestimate `estimateSize` - prevents scroll jumps (items shrinking causes issues)
2. Increase `overscan` (3-5) to reduce blank flashing during fast scrolling
3. Use `transform: translateY()` over top for GPU-composited positioning
4. Add `data-index` attribute when using measureElement for dynamic sizing
5. Don't set fixed height on dynamically measured items
6. Use `getItemKey` for stable keys when items can reorder
7. Use `gap` option instead of margins (margins interfere with measurement)
8. Use `paddingStart/End` instead of CSS padding on the container
9. Use `enabled: false` to pause when the list is hidden
10. Memoize callbacks (estimateSize, getItemKey, rangeExtractor)
11. Use `will-change: transform` CSS on items for GPU acceleration

Common Pitfalls

• Setting fixed height on dynamically measured items
• Using CSS margins instead of the gap option
• Forgetting data-index with measureElement
• Not providing position: relative on the inner container
• Underestimating estimateSize (causes scroll jumps)
• Setting overscan too low for fast scrolling (blank items)
• Forgetting to subtract scrollMargin from translateY in window scrolling
• Not memoizing the estimateSize function (causes re-renders)