<!-- 等待頁面渲染完才進行滾動的操作 -->
 router.app.$nextTick(() => {
   <!-- 初始化數(shù)據(jù) -->
  const position = getScrollPosition()
  const shouldScroll = behavior.call(router, to, from, isPop ? position : null)

  if (!shouldScroll) {
   return
  }
  <!-- 判斷是否是Promise,官網(wǎng)說支持異步 -->
  if (typeof shouldScroll.then === 'function') {
   shouldScroll.then(shouldScroll => {
    scrollToPosition((shouldScroll: any), position)
   }).catch(err => {
    if (process.env.NODE_ENV !== 'production') {
     assert(false, err.toString())
    }
   })
  } else {
   scrollToPosition(shouldScroll, position)
  }
 })

function scrollToPosition (shouldScroll, position) {
 const isObject = typeof shouldScroll === 'object'
 <!-- 對position進行初始化的操作 -->
 if (isObject && typeof shouldScroll.selector === 'string') {
  const el = document.querySelector(shouldScroll.selector)
  if (el) {
   let offset = shouldScroll.offset && typeof shouldScroll.offset === 'object' ? shouldScroll.offset : {}
   offset = normalizeOffset(offset)
   position = getElementPosition(el, offset)
  } else if (isValidPosition(shouldScroll)) {
   position = normalizePosition(shouldScroll)
  }
 } else if (isObject && isValidPosition(shouldScroll)) {
  position = normalizePosition(shouldScroll)
 }
  使用window.scrollTo來進行滾動處理
 if (position) {
  window.scrollTo(position.x, position.y)
 }
}

export function pushState (url?: string, replace?: boolean) {
  <!-- 保存當前頁面的滾動位置 -->
 saveScrollPosition()
 // try...catch the pushState call to get around Safari
 // DOM Exception 18 where it limits to 100 pushState calls
 const history = window.history
 try {
   <!-- 判斷是哪種操作動作 -->
  if (replace) {
   history.replaceState({ key: _key }, '', url)
  } else {
   _key = genKey()
   history.pushState({ key: _key }, '', url)
  }
 } catch (e) {
  window.location[replace ? 'replace' : 'assign'](url)
 }
}

function pushHash (path) {
 if (supportsPushState) {
  pushState(getUrl(path))
 } else {
  window.location.hash = path
 }
}