What's virtualized?

Virtualized tables only render what's visible — rows and columns outside the viewport are removed from the DOM entirely. Trying to read a cell that isn't rendered will give you nothing.

Playwright Smart Table handles this with a viewport strategy. You describe what's currently in the DOM, and the library scrolls before it reads.

ViewportStrategy

Implement whichever of these four functions your grid exposes — all are optional:

strategies: {
  viewport: {
    // Return the 0-based index range of rows currently rendered in the DOM
    getVisibleRowRange: async ({ root }) => {
      return root.evaluate(el => {
        const rows = [...el.querySelectorAll('[role="row"]')]
        const indices = rows
          .map(r => Number(r.getAttribute('aria-rowindex')) - 1)
          .filter(n => !isNaN(n))
        return { first: Math.min(...indices), last: Math.max(...indices) }
      })
    },

    // Return the 0-based index range of columns currently rendered in the DOM
    getVisibleColumnRange: async ({ root }) => {
      return root.evaluate(el => {
        const cells = [...el.querySelectorAll('[role="gridcell"]')]
        const indices = cells
          .map(c => Number(c.getAttribute('aria-colindex')) - 1)
          .filter(n => !isNaN(n))
        return { first: Math.min(...indices), last: Math.max(...indices) }
      })
    },

    // Scroll to make a specific row visible
    scrollToRow: async ({ root }, rowIndex) => {
      await root.locator(`[aria-rowindex="${rowIndex + 1}"]`).scrollIntoViewIfNeeded()
    },

    // Scroll to make a specific column visible
    scrollToColumn: async ({ root }, colIndex) => {
      await root.locator(`[aria-colindex="${colIndex + 1}"]`).first().scrollIntoViewIfNeeded()
    },
  }
}

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Built-in strategies Shortcut

If your grid stamps rows and cells with a DOM attribute containing their index (like aria-rowindex, data-index, or similar), Strategies.Viewport.dataAttribute() implements all four functions for you:

strategies: {
  viewport: Strategies.Viewport.dataAttribute({
    scrollContainer: '.MuiDataGrid-virtualScroller',
    rowAttribute: 'aria-rowindex',
    columnAttribute: 'aria-colindex',
    rowOffset: 1,
    columnOffset: 1,
  })
}

strategies: {
  viewport: Strategies.Viewport.dataAttribute({
    scrollContainer: '#table-scroller',
  })
}

Config: strategies.viewport

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Viewport freshness and caching

Viewport geometry is queried again for each cell navigation, and visible row membership is queried again for each scan. External scrolling, sorting, reset, and revalidation therefore cannot reuse geometry or membership from an earlier operation.

Within one navigation, the library memoizes repeated range queries to reduce DOM round-trips. Both ranges are cleared before and after scrolling either axis, including a failed scroll. Set strategies.viewport.disableCache: true to bypass this in-navigation memoization.

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Which row is which?

In a virtualized table, the 3rd <tr> in the DOM isn't row 3 — it's whatever happens to be rendered in that slot right now. Scroll a little and the same element can be holding a completely different row.

If your grid stamps each row with its real position (data-rowindex, aria-rowindex, and so on), tell us how to read it:

strategies: {
  resolveRowIndex: async (row) => {
    const v = await row.getAttribute('data-rowindex')
    if (!v?.trim() || !Number.isFinite(Number(v))) return undefined // not a real data row yet
    return { index: Number(v), selector: `[data-rowindex="${v}"]` }
  }
}

Returning a selector alongside the index makes the row self-healing. Instead of holding onto whichever element it found, the row re-finds itself by that attribute every time you use it — so getCell(), toJSON(), and smartFill() keep pointing at the right row even after the grid recycles its DOM. Return just a number if you only need the index.

This is also what lets you ask for a row by its real position with findRowByIndex.

Config: strategies.resolveRowIndex

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→ API Reference: Strategies — viewport · Strategies — resolveRowIndex