Function getVirtualRange

packages/app-core/src/lib/virtual-list.ts:15–40

({
  itemCount,
  itemSize,
  scrollTop,
  viewportHeight,
  overscan = 6
}: VirtualRangeInput)

}

export function getVirtualRange({
  itemCount,
  itemSize,
  scrollTop,
  viewportHeight,
  overscan = 6
}: VirtualRangeInput): VirtualRange {
  const count = Math.max(0, Math.floor(itemCount))
  if (count === 0) return { start: 0, end: 0, totalSize: 0 }

  const size = Math.max(1, itemSize)
  const safeScrollTop = Math.max(0, scrollTop)
  const safeOverscan = Math.max(0, Math.floor(overscan))
  const visibleStart = Math.min(count - 1, Math.floor(safeScrollTop / size))
  const visibleCount =
    viewportHeight > 0 ? Math.max(1, Math.ceil(viewportHeight / size)) : safeOverscan + 1

  const start = Math.max(0, visibleStart - safeOverscan)
  const end = Math.min(count, visibleStart + visibleCount + safeOverscan)

  return {
    start,
    end,
    totalSize: count * size
  }
}

export interface VirtualIndexScrollInput {
  index: number