element-plus/packages/utils/dom/scroll.ts

import { isClient } from '@vueuse/core'
import { getStyle } from './style'

export const isScroll = (el: HTMLElement, isVertical?: boolean): boolean => {
  if (!isClient) return false

  const key = (
    {
      undefined: 'overflow',
      true: 'overflow-y',
      false: 'overflow-x',
    } as const
  )[String(isVertical)]!
  const overflow = getStyle(el, key)
  return ['scroll', 'auto', 'overlay'].some((s) => overflow.includes(s))
}

export const getScrollContainer = (
  el: HTMLElement,
  isVertical?: boolean
): Window | HTMLElement | undefined => {
  if (!isClient) return

  let parent: HTMLElement = el
  while (parent) {
    if ([window, document, document.documentElement].includes(parent))
      return window

    if (isScroll(parent, isVertical)) return parent

    parent = parent.parentNode as HTMLElement
  }

  return parent
}

let scrollBarWidth: number
export const getScrollBarWidth = (): number => {
  if (!isClient) return 0
  if (scrollBarWidth !== undefined) return scrollBarWidth

  const outer = document.createElement('div')
  outer.className = 'el-scrollbar__wrap'
  outer.style.visibility = 'hidden'
  outer.style.width = '100px'
  outer.style.position = 'absolute'
  outer.style.top = '-9999px'
  document.body.appendChild(outer)

  const widthNoScroll = outer.offsetWidth
  outer.style.overflow = 'scroll'

  const inner = document.createElement('div')
  inner.style.width = '100%'
  outer.appendChild(inner)

  const widthWithScroll = inner.offsetWidth
  outer.parentNode?.removeChild(outer)
  scrollBarWidth = widthNoScroll - widthWithScroll

  return scrollBarWidth
}