element-plus/packages/utils/scrollbar-width.ts

import { isClient } from '@vueuse/core'

let scrollBarWidth: number

export default function (): 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
}