Function computeVirtualScrollOffsets

src/hooks/useVirtualScroll.ts:304–342

(
  itemKeys: readonly string[],
  heightCache: ReadonlyMap<string, number>,
  previous: VirtualScrollOffsetsState,
  version: number,
)

}

export function computeVirtualScrollOffsets(
  itemKeys: readonly string[],
  heightCache: ReadonlyMap<string, number>,
  previous: VirtualScrollOffsetsState,
  version: number,
): VirtualScrollOffsetsState {
  const n = itemKeys.length
  if (previous.version === version && previous.n === n) {
    return previous
  }

  const canAppend =
    previous.version === version &&
    previous.n >= 0 &&
    n > previous.n &&
    previous.arr.length >= previous.n + 1

  const arr =
    previous.arr.length >= n + 1
      ? previous.arr
      : new Float64Array(n + 1)

  if (canAppend) {
    if (arr !== previous.arr) {
      arr.set(previous.arr.subarray(0, previous.n + 1))
    }
    for (let i = previous.n; i < n; i++) {
      arr[i + 1] =
        arr[i]! + (heightCache.get(itemKeys[i]!) ?? DEFAULT_ESTIMATE)
    }
    return { arr, version, n }
  }

  arr[0] = 0
  for (let i = 0; i < n; i++) {
    arr[i + 1] = arr[i]! + (heightCache.get(itemKeys[i]!) ?? DEFAULT_ESTIMATE)
  }
  return { arr, version, n }
}

export function computeVirtualScrollRenderPolicy({
  start,