text: /**
   * Virtual DOM patching algorithm based on Snabbdom by
   * Simon Friis Vindum (@paldepind)
   * Licensed under the MIT License
   * https://github.com/paldepind/snabbdom/blob/master/LICENSE
   *
   * modified by Evan You (@yyx990803)
   *
   * Not type-checking this because this file is perf-critical and the cost
   * of making flow understand it is not worth it.
   */
  
  import VNode, { cloneVNode } from './vnode'
  import config from '../config'
  import { SSR_ATTR } from 'shared/constants'
  import { registerRef } from './modules/ref'
  import { traverse } from '../observer/traverse'
  import { activeInstance } from '../instance/lifecycle'
  import { isTextInputType } from 'web/util/element'
  
  import {
    warn,
    isDef,
    isUndef,
    isTrue,
    makeMap,
    isRegExp,
    isPrimitive
  } from '../util/index'
  
  export const emptyNode = new VNode('', {}, [])
  
  const hooks = ['create', 'activate', 'update', 'remove', 'destroy']
  
  function sameVnode (a, b) {
    return (
      a.key === b.key && (
        (
          a.tag === b.tag &&
          a.isComment === b.isComment &&
          isDef(a.data) === isDef(b.data) &&
          sameInputType(a, b)
        ) || (
          isTrue(a.isAsyncPlaceholder) &&
          a.asyncFactory === b.asyncFactory &&
          isUndef(b.asyncFactory.error)
        )
      )
    )
  }
  
  function sameInputType (a, b) {
    if (a.tag !== 'input') return true
    let i
    const typeA = isDef(i = a.data) && isDef(i = i.attrs) && i.type
    const typeB = isDef(i = b.data) && isDef(i = i.attrs) && i.type
    return typeA === typeB || isTextInputType(typeA) && isTextInputType(typeB)
  }
  
  function createKeyToOldIdx (children, beginIdx, endIdx) {
    let i, key
    const map = {}
    for (i = beginIdx; i <= endIdx; ++i) {
      key = children[i].key
      if (isDef(key)) map[key] = i
    }
    return map
  }
  
  export function createPatchFunction (backend) {
    let i, j
    const cbs = {}
  
    const { modules, nodeOps } = backend
  
    for (i = 0; i < hooks.length; ++i) {
      cbs[hooks[i]] = []
      for (j = 0; j < modules.length; ++j) {
        if (isDef(modules[j][hooks[i]])) {
          cbs[hooks[i]].push(modules[j][hooks[i]])
        }
      }
    }
  
    function emptyNodeAt (elm) {
      return new VNode(nodeOps.tagName(elm).toLowerCase(), {}, [], undefined, elm)
    }
  
    function createRmCb (childElm, listeners) {
      function remove () {
        if (--remove.listeners === 0) {
          removeNode(childElm)
        }
      }
      remove.listeners = listeners
      return remove
    }
  
    function removeNode (el) {
      const parent = nodeOps.parentNode(el)
      // element may have already been removed due to v-html / v-text
      if (isDef(parent)) {
        nodeOps.removeChild(parent, el)
      }
    }
  
    function isUnknownElement (vnode, inVPre) {
      return (
        !inVPre &&
        !vnode.ns &&
        !(
          config.ignoredElements.length &&
          config.ignoredElements.some(ignore => {
            return isRegExp(ignore)
              ? ignore.test(vnode.tag)
              : ignore === vnode.tag
          })
        ) &&
        config.isUnknownElement(vnode.tag)
      )
    }
  
    let creatingElmInVPre = 0
  
    function createElm (
      vnode,
      insertedVnodeQueue,
      parentElm,
      refElm,
      nested,
      ownerArray,
      index
    ) {
      if (isDef(vnode.elm) && isDef(ownerArray)) {
        // This vnode was used in a previous render!
        // now it's used as a new node, overwriting its elm would cause
        // potential patch errors down the road when it's used as an insertion
        // reference node. Instead, we clone the node on-demand before creating
        // associated DOM element for it.
        vnode = ownerArray[index] = cloneVNode(vnode)
      }
  
      vnode.isRootInsert = !nested // for transition enter check
      if (createComponent(vnode, insertedVnodeQueue, parentElm, refElm)) {
        return
      }
  
      const data = vnode.data
      const children = vnode.children
      const tag = vnode.tag
      if (isDef(tag)) {
        if (process.env.NODE_ENV !== 'production') {
          if (data && data.pre) {
            creatingElmInVPre++
          }
          if (isUnknownElement(vnode, creatingElmInVPre)) {
            warn(
              'Unknown custom element: <' + tag + '> - did you ' +
              'register the component correctly? For recursive components, ' +
              'make sure to provide the "name" option.',
              vnode.context
            )
          }
        }
  
        vnode.elm = vnode.ns
          ? nodeOps.createElementNS(vnode.ns, tag)
          : nodeOps.createElement(tag, vnode)
        setScope(vnode)
  
        /* istanbul ignore if */
        if (__WEEX__) {
          // in Weex, the default insertion order is parent-first.
          // List items can be optimized to use children-first insertion
          // with append="tree".
          const appendAsTree = isDef(data) && isTrue(data.appendAsTree)
          if (!appendAsTree) {
            if (isDef(data)) {
              invokeCreateHooks(vnode, insertedVnodeQueue)
            }
            insert(parentElm, vnode.elm, refElm)
          }
          createChildren(vnode, children, insertedVnodeQueue)
          if (appendAsTree) {
            if (isDef(data)) {
              invokeCreateHooks(vnode, insertedVnodeQueue)
            }
            insert(parentElm, vnode.elm, refElm)
          }
        } else {
          createChildren(vnode, children, insertedVnodeQueue)
          if (isDef(data)) {
            invokeCreateHooks(vnode, insertedVnodeQueue)
          }
          insert(parentElm, vnode.elm, refElm)
        }
  
        if (process.env.NODE_ENV !== 'production' && data && data.pre) {
          creatingElmInVPre--
        }
      } else if (isTrue(vnode.isComment)) {
        vnode.elm = nodeOps.createComment(vnode.text)
        insert(parentElm, vnode.elm, refElm)
      } else {
        vnode.elm = nodeOps.createTextNode(vnode.text)
        insert(parentElm, vnode.elm, refElm)
      }
    }
  
    function createComponent (vnode, insertedVnodeQueue, parentElm, refElm) {
      let i = vnode.data
      if (isDef(i)) {
        const isReactivated = isDef(vnode.componentInstance) && i.keepAlive
        if (isDef(i = i.hook) && isDef(i = i.init)) {
          i(vnode, false /* hydrating */)
        }
        // after calling the init hook, if the vnode is a child component
        // it should've created a child instance and mounted it. the child
        // component also has set the placeholder vnode's elm.
        // in that case we can just return the element and be done.
        if (isDef(vnode.componentInstance)) {
          initComponent(vnode, insertedVnodeQueue)
          insert(parentElm, vnode.elm, refElm)
          if (isTrue(isReactivated)) {
            reactivateComponent(vnode, insertedVnodeQueue, parentElm, refElm)
          }
          return true
        }
      }
    }
  
    function initComponent (vnode, insertedVnodeQueue) {
      if (isDef(vnode.data.pendingInsert)) {
        insertedVnodeQueue.push.apply(insertedVnodeQueue, vnode.data.pendingInsert)
        vnode.data.pendingInsert = null
      }
      vnode.elm = vnode.componentInstance.$el
      if (isPatchable(vnode)) {
        invokeCreateHooks(vnode, insertedVnodeQueue)
        setScope(vnode)
      } else {
        // empty component root.
        // skip all element-related modules except for ref (#3455)
        registerRef(vnode)
        // make sure to invoke the insert hook
        insertedVnodeQueue.push(vnode)
      }
    }
  
    function reactivateComponent (vnode, insertedVnodeQueue, parentElm, refElm) {
      let i
      // hack for #4339: a reactivated component with inner transition
      // does not trigger because the inner node's created hooks are not called
      // again. It's not ideal to involve module-specific logic in here but
      // there doesn't seem to be a better way to do it.
      let innerNode = vnode
      while (innerNode.componentInstance) {
        innerNode = innerNode.componentInstance._vnode
        if (isDef(i = innerNode.data) && isDef(i = i.transition)) {
          for (i = 0; i < cbs.activate.length; ++i) {
            cbs.activate[i](emptyNode, innerNode)
          }
          insertedVnodeQueue.push(innerNode)
          break
        }
      }
      // unlike a newly created component,
      // a reactivated keep-alive component doesn't insert itself
      insert(parentElm, vnode.elm, refElm)
    }
  
    function insert (parent, elm, ref) {
      if (isDef(parent)) {
        if (isDef(ref)) {
          if (ref.parentNode === parent) {
            nodeOps.insertBefore(parent, elm, ref)
          }
        } else {
          nodeOps.appendChild(parent, elm)
        }
      }
    }
  
    function createChildren (vnode, children, insertedVnodeQueue) {
      if (Array.isArray(children)) {
        if (process.env.NODE_ENV !== 'production') {
          checkDuplicateKeys(children)
        }
        for (let i = 0; i < children.length; ++i) {
          createElm(children[i], insertedVnodeQueue, vnode.elm, null, true, children, i)
        }
      } else if (isPrimitive(vnode.text)) {
        nodeOps.appendChild(vnode.elm, nodeOps.createTextNode(String(vnode.text)))
      }
    }
  
    function isPatchable (vnode) {
      while (vnode.componentInstance) {
        vnode = vnode.componentInstance._vnode
      }
      return isDef(vnode.tag)
    }
  
    function invokeCreateHooks (vnode, insertedVnodeQueue) {
      for (let i = 0; i < cbs.create.length; ++i) {
        cbs.create[i](emptyNode, vnode)
      }
      i = vnode.data.hook // Reuse variable
      if (isDef(i)) {
        if (isDef(i.create)) i.create(emptyNode, vnode)
        if (isDef(i.insert)) insertedVnodeQueue.push(vnode)
      }
    }
  
    // set scope id attribute for scoped CSS.
    // this is implemented as a special case to avoid the overhead
    // of going through the normal attribute patching process.
    function setScope (vnode) {
      let i
      if (isDef(i = vnode.fnScopeId)) {
        nodeOps.setStyleScope(vnode.elm, i)
      } else {
        let ancestor = vnode
        while (ancestor) {
          if (isDef(i = ancestor.context) && isDef(i = i.$options._scopeId)) {
            nodeOps.setStyleScope(vnode.elm, i)
          }
          ancestor = ancestor.parent
        }
      }
      // for slot content they should also get the scopeId from the host instance.
      if (isDef(i = activeInstance) &&
        i !== vnode.context &&
        i !== vnode.fnContext &&
        isDef(i = i.$options._scopeId)
      ) {
        nodeOps.setStyleScope(vnode.elm, i)
      }
    }
  
    function addVnodes (parentElm, refElm, vnodes, startIdx, endIdx, insertedVnodeQueue) {
      for (; startIdx <= endIdx; ++startIdx) {
        createElm(vnodes[startIdx], insertedVnodeQueue, parentElm, refElm, false, vnodes, startIdx)
      }
    }
  
    function invokeDestroyHook (vnode) {
      let i, j
      const data = vnode.data
      if (isDef(data)) {
        if (isDef(i = data.hook) && isDef(i = i.destroy)) i(vnode)
        for (i = 0; i < cbs.destroy.length; ++i) cbs.destroy[i](vnode)
      }
      if (isDef(i = vnode.children)) {
        for (j = 0; j < vnode.children.length; ++j) {
          invokeDestroyHook(vnode.children[j])
        }
      }
    }
  
    function removeVnodes (parentElm, vnodes, startIdx, endIdx) {
      for (; startIdx <= endIdx; ++startIdx) {
        const ch = vnodes[startIdx]
        if (isDef(ch)) {
          if (isDef(ch.tag)) {
            removeAndInvokeRemoveHook(ch)
            invokeDestroyHook(ch)
          } else { // Text node
            removeNode(ch.elm)
          }
        }
      }
    }
  
    function removeAndInvokeRemoveHook (vnode, rm) {
      if (isDef(rm) || isDef(vnode.data)) {
        let i
        const listeners = cbs.remove.length + 1
        if (isDef(rm)) {
          // we have a recursively passed down rm callback
          // increase the listeners count
          rm.listeners += listeners
        } else {
          // directly removing
          rm = createRmCb(vnode.elm, listeners)
        }
        // recursively invoke hooks on child component root node
        if (isDef(i = vnode.componentInstance) && isDef(i = i._vnode) && isDef(i.data)) {
          removeAndInvokeRemoveHook(i, rm)
        }
        for (i = 0; i < cbs.remove.length; ++i) {
          cbs.remove[i](vnode, rm)
        }
        if (isDef(i = vnode.data.hook) && isDef(i = i.remove)) {
          i(vnode, rm)
        } else {
          rm()
        }
      } else {
        removeNode(vnode.elm)
      }
    }
  
    function updateChildren (parentElm, oldCh, newCh, insertedVnodeQueue, removeOnly) {
      let oldStartIdx = 0
      let newStartIdx = 0
      let oldEndIdx = oldCh.length - 1
      let oldStartVnode = oldCh[0]
      let oldEndVnode = oldCh[oldEndIdx]
      let newEndIdx = newCh.length - 1
      let newStartVnode = newCh[0]
      let newEndVnode = newCh[newEndIdx]
      let oldKeyToIdx, idxInOld, vnodeToMove, refElm
  
      // removeOnly is a special flag used only by <transition-group>
      // to ensure removed elements stay in correct relative positions
      // during leaving transitions
      const canMove = !removeOnly
  
      if (process.env.NODE_ENV !== 'production') {
        checkDuplicateKeys(newCh)
      }
  
      while (oldStartIdx <= oldEndIdx && newStartIdx <= newEndIdx) {
        if (isUndef(oldStartVnode)) {
          oldStartVnode = oldCh[++oldStartIdx] // Vnode has been moved left
        } else if (isUndef(oldEndVnode)) {
          oldEndVnode = oldCh[--oldEndIdx]
        } else if (sameVnode(oldStartVnode, newStartVnode)) {
          patchVnode(oldStartVnode, newStartVnode, insertedVnodeQueue)
          oldStartVnode = oldCh[++oldStartIdx]
          newStartVnode = newCh[++newStartIdx]
        } else if (sameVnode(oldEndVnode, newEndVnode)) {
          patchVnode(oldEndVnode, newEndVnode, insertedVnodeQueue)
          oldEndVnode = oldCh[--oldEndIdx]
          newEndVnode = newCh[--newEndIdx]
        } else if (sameVnode(oldStartVnode, newEndVnode)) { // Vnode moved right
          patchVnode(oldStartVnode, newEndVnode, insertedVnodeQueue)
          canMove && nodeOps.insertBefore(parentElm, oldStartVnode.elm, nodeOps.nextSibling(oldEndVnode.elm))
          oldStartVnode = oldCh[++oldStartIdx]
          newEndVnode = newCh[--newEndIdx]
        } else if (sameVnode(oldEndVnode, newStartVnode)) { // Vnode moved left
          patchVnode(oldEndVnode, newStartVnode, insertedVnodeQueue)
          canMove && nodeOps.insertBefore(parentElm, oldEndVnode.elm, oldStartVnode.elm)
          oldEndVnode = oldCh[--oldEndIdx]
          newStartVnode = newCh[++newStartIdx]
        } else {
          if (isUndef(oldKeyToIdx)) oldKeyToIdx = createKeyToOldIdx(oldCh, oldStartIdx, oldEndIdx)
          idxInOld = isDef(newStartVnode.key)
            ? oldKeyToIdx[newStartVnode.key]
            : findIdxInOld(newStartVnode, oldCh, oldStartIdx, oldEndIdx)
          if (isUndef(idxInOld)) { // New element
            createElm(newStartVnode, insertedVnodeQueue, parentElm, oldStartVnode.elm, false, newCh, newStartIdx)
          } else {
            vnodeToMove = oldCh[idxInOld]
            if (sameVnode(vnodeToMove, newStartVnode)) {
              patchVnode(vnodeToMove, newStartVnode, insertedVnodeQueue)
              oldCh[idxInOld] = undefined
              canMove && nodeOps.insertBefore(parentElm, vnodeToMove.elm, oldStartVnode.elm)
            } else {
              // same key but different element. treat as new element
              createElm(newStartVnode, insertedVnodeQueue, parentElm, oldStartVnode.elm, false, newCh, newStartIdx)
            }
          }
          newStartVnode = newCh[++newStartIdx]
        }
      }
      if (oldStartIdx > oldEndIdx) {
        refElm = isUndef(newCh[newEndIdx + 1]) ? null : newCh[newEndIdx + 1].elm
        addVnodes(parentElm, refElm, newCh, newStartIdx, newEndIdx, insertedVnodeQueue)
      } else if (newStartIdx > newEndIdx) {
        removeVnodes(parentElm, oldCh, oldStartIdx, oldEndIdx)
      }
    }
  
    function checkDuplicateKeys (children) {
      const seenKeys = {}
      for (let i = 0; i < children.length; i++) {
        const vnode = children[i]
        const key = vnode.key
        if (isDef(key)) {
          if (seenKeys[key]) {
            warn(
              `Duplicate keys detected: '${key}'. This may cause an update error.`,
              vnode.context
            )
          } else {
            seenKeys[key] = true
          }
        }
      }
    }
  
    function findIdxInOld (node, oldCh, start, end) {
      for (let i = start; i < end; i++) {
        const c = oldCh[i]
        if (isDef(c) && sameVnode(node, c)) return i
      }
    }
  
    function patchVnode (oldVnode, vnode, insertedVnodeQueue, removeOnly) {
      if (oldVnode === vnode) {
        return
      }
  
      const elm = vnode.elm = oldVnode.elm
  
      if (isTrue(oldVnode.isAsyncPlaceholder)) {
        if (isDef(vnode.asyncFactory.resolved)) {
          hydrate(oldVnode.elm, vnode, insertedVnodeQueue)
        } else {
          vnode.isAsyncPlaceholder = true
        }
        return
      }
  
      // reuse element for static trees.
      // note we only do this if the vnode is cloned -
      // if the new node is not cloned it means the render functions have been
      // reset by the hot-reload-api and we need to do a proper re-render.
      if (isTrue(vnode.isStatic) &&
        isTrue(oldVnode.isStatic) &&
        vnode.key === oldVnode.key &&
        (isTrue(vnode.isCloned) || isTrue(vnode.isOnce))
      ) {
        vnode.componentInstance = oldVnode.componentInstance
        return
      }
  
      let i
      const data = vnode.data
      if (isDef(data) && isDef(i = data.hook) && isDef(i = i.prepatch)) {
        i(oldVnode, vnode)
      }
  
      const oldCh = oldVnode.children
      const ch = vnode.children
      if (isDef(data) && isPatchable(vnode)) {
        for (i = 0; i < cbs.update.length; ++i) cbs.update[i](oldVnode, vnode)
        if (isDef(i = data.hook) && isDef(i = i.update)) i(oldVnode, vnode)
      }
      if (isUndef(vnode.text)) {
        if (isDef(oldCh) && isDef(ch)) {
          if (oldCh !== ch) updateChildren(elm, oldCh, ch, insertedVnodeQueue, removeOnly)
        } else if (isDef(ch)) {
          if (isDef(oldVnode.text)) nodeOps.setTextContent(elm, '')
          addVnodes(elm, null, ch, 0, ch.length - 1, insertedVnodeQueue)
        } else if (isDef(oldCh)) {
          removeVnodes(elm, oldCh, 0, oldCh.length - 1)
        } else if (isDef(oldVnode.text)) {
          nodeOps.setTextContent(elm, '')
        }
      } else if (oldVnode.text !== vnode.text) {
        nodeOps.setTextContent(elm, vnode.text)
      }
      if (isDef(data)) {
        if (isDef(i = data.hook) && isDef(i = i.postpatch)) i(oldVnode, vnode)
      }
    }
  
    function invokeInsertHook (vnode, queue, initial) {
      // delay insert hooks for component root nodes, invoke them after the
      // element is really inserted
      if (isTrue(initial) && isDef(vnode.parent)) {
        vnode.parent.data.pendingInsert = queue
      } else {
        for (let i = 0; i < queue.length; ++i) {
          queue[i].data.hook.insert(queue[i])
        }
      }
    }
  
    let hydrationBailed = false
    // list of modules that can skip create hook during hydration because they
    // are already rendered on the client or has no need for initialization
    // Note: style is excluded because it relies on initial clone for future
    // deep updates (#7063).
    const isRenderedModule = makeMap('attrs,class,staticClass,staticStyle,key')
  
    // Note: this is a browser-only function so we can assume elms are DOM nodes.
    function hydrate (elm, vnode, insertedVnodeQueue, inVPre) {
      let i
      const { tag, data, children } = vnode
      inVPre = inVPre || (data && data.pre)
      vnode.elm = elm
  
      if (isTrue(vnode.isComment) && isDef(vnode.asyncFactory)) {
        vnode.isAsyncPlaceholder = true
        return true
      }
      // assert node match
      if (process.env.NODE_ENV !== 'production') {
        if (!assertNodeMatch(elm, vnode, inVPre)) {
          return false
        }
      }
      if (isDef(data)) {
        if (isDef(i = data.hook) && isDef(i = i.init)) i(vnode, true /* hydrating */)
        if (isDef(i = vnode.componentInstance)) {
          // child component. it should have hydrated its own tree.
          initComponent(vnode, insertedVnodeQueue)
          return true
        }
      }
      if (isDef(tag)) {
        if (isDef(children)) {
          // empty element, allow client to pick up and populate children
          if (!elm.hasChildNodes()) {
            createChildren(vnode, children, insertedVnodeQueue)
          } else {
            // v-html and domProps: innerHTML
            if (isDef(i = data) && isDef(i = i.domProps) && isDef(i = i.innerHTML)) {
              if (i !== elm.innerHTML) {
                /* istanbul ignore if */
                if (process.env.NODE_ENV !== 'production' &&
                  typeof console !== 'undefined' &&
                  !hydrationBailed
                ) {
                  hydrationBailed = true
                  console.warn('Parent: ', elm)
                  console.warn('server innerHTML: ', i)
                  console.warn('client innerHTML: ', elm.innerHTML)
                }
                return false
              }
            } else {
              // iterate and compare children lists
              let childrenMatch = true
              let childNode = elm.firstChild
              for (let i = 0; i < children.length; i++) {
                if (!childNode || !hydrate(childNode, children[i], insertedVnodeQueue, inVPre)) {
                  childrenMatch = false
                  break
                }
                childNode = childNode.nextSibling
              }
              // if childNode is not null, it means the actual childNodes list is
              // longer than the virtual children list.
              if (!childrenMatch || childNode) {
                /* istanbul ignore if */
                if (process.env.NODE_ENV !== 'production' &&
                  typeof console !== 'undefined' &&
                  !hydrationBailed
                ) {
                  hydrationBailed = true
                  console.warn('Parent: ', elm)
                  console.warn('Mismatching childNodes vs. VNodes: ', elm.childNodes, children)
                }
                return false
              }
            }
          }
        }
        if (isDef(data)) {
          let fullInvoke = false
          for (const key in data) {
            if (!isRenderedModule(key)) {
              fullInvoke = true
              invokeCreateHooks(vnode, insertedVnodeQueue)
              break
            }
          }
          if (!fullInvoke && data['class']) {
            // ensure collecting deps for deep class bindings for future updates
            traverse(data['class'])
          }
        }
      } else if (elm.data !== vnode.text) {
        elm.data = vnode.text
      }
      return true
    }
  
    function assertNodeMatch (node, vnode, inVPre) {
      if (isDef(vnode.tag)) {
        return vnode.tag.indexOf('vue-component') === 0 || (
          !isUnknownElement(vnode, inVPre) &&
          vnode.tag.toLowerCase() === (node.tagName && node.tagName.toLowerCase())
        )
      } else {
        return node.nodeType === (vnode.isComment ? 8 : 3)
      }
    }
  
    return function patch (oldVnode, vnode, hydrating, removeOnly) {
      if (isUndef(vnode)) {
        if (isDef(oldVnode)) invokeDestroyHook(oldVnode)
        return
      }
  
      let isInitialPatch = false
      const insertedVnodeQueue = []
  
      if (isUndef(oldVnode)) {
        // empty mount (likely as component), create new root element
        isInitialPatch = true
        createElm(vnode, insertedVnodeQueue)
      } else {
        
        const isRealElement = isDef(oldVnode.nodeType)
        if (!isRealElement && sameVnode(oldVnode, vnode)) {
          // patch existing root node
          patchVnode(oldVnode, vnode, insertedVnodeQueue, removeOnly)
        } else {
          if (isRealElement) {
            // mounting to a real element
            // check if this is server-rendered content and if we can perform
            // a successful hydration.
            if (oldVnode.nodeType === 1 && oldVnode.hasAttribute(SSR_ATTR)) {
              oldVnode.removeAttribute(SSR_ATTR)
              hydrating = true
            }
            if (isTrue(hydrating)) {
              if (hydrate(oldVnode, vnode, insertedVnodeQueue)) {
                invokeInsertHook(vnode, insertedVnodeQueue, true)
                return oldVnode
              } else if (process.env.NODE_ENV !== 'production') {
                warn(
                  'The client-side rendered virtual DOM tree is not matching ' +
                  'server-rendered content. This is likely caused by incorrect ' +
                  'HTML markup, for example nesting block-level elements inside ' +
                  '<p>, or missing <tbody>. Bailing hydration and performing ' +
                  'full client-side render.'
                )
              }
            }
            // either not server-rendered, or hydration failed.
            // create an empty node and replace it
            oldVnode = emptyNodeAt(oldVnode)
          }
  
          // replacing existing element
          const oldElm = oldVnode.elm
          const parentElm = nodeOps.parentNode(oldElm)
  
          // create new node
          createElm(
            vnode,
            insertedVnodeQueue,
            // extremely rare edge case: do not insert if old element is in a
            // leaving transition. Only happens when combining transition +
            // keep-alive + HOCs. (#4590)
            oldElm._leaveCb ? null : parentElm,
            nodeOps.nextSibling(oldElm)
          )
  
          // update parent placeholder node element, recursively
          if (isDef(vnode.parent)) {
            let ancestor = vnode.parent
            const patchable = isPatchable(vnode)
            while (ancestor) {
              for (let i = 0; i < cbs.destroy.length; ++i) {
                cbs.destroy[i](ancestor)
              }
              ancestor.elm = vnode.elm
              if (patchable) {
                for (let i = 0; i < cbs.create.length; ++i) {
                  cbs.create[i](emptyNode, ancestor)
                }
                // #6513
                // invoke insert hooks that may have been merged by create hooks.
                // e.g. for directives that uses the "inserted" hook.
                const insert = ancestor.data.hook.insert
                if (insert.merged) {
                  // start at index 1 to avoid re-invoking component mounted hook
                  for (let i = 1; i < insert.fns.length; i++) {
                    insert.fns[i]()
                  }
                }
              } else {
                registerRef(ancestor)
              }
              ancestor = ancestor.parent
            }
          }
  
          // destroy old node
          if (isDef(parentElm)) {
            removeVnodes(parentElm, [oldVnode], 0, 0)
          } else if (isDef(oldVnode.tag)) {
            invokeDestroyHook(oldVnode)
          }
        }
      }
  
      invokeInsertHook(vnode, insertedVnodeQueue, isInitialPatch)
      return vnode.elm
    }
  }
  