vue2-datepicker/src/utils/scroll-into-view.js

export default function scrollIntoView (container, selected) {
  if (!selected) {
    container.scrollTop = 0
    return
  }

  const offsetParents = []
  let pointer = selected.offsetParent
  while (pointer && container !== pointer && container.contains(pointer)) {
    offsetParents.push(pointer)
    pointer = pointer.offsetParent
  }
  const top = selected.offsetTop + offsetParents.reduce((prev, curr) => (prev + curr.offsetTop), 0)
  const bottom = top + selected.offsetHeight
  const viewRectTop = container.scrollTop
  const viewRectBottom = viewRectTop + container.clientHeight

  if (top < viewRectTop) {
    container.scrollTop = top
  } else if (bottom > viewRectBottom) {
    container.scrollTop = bottom - container.clientHeight
  }
}