function sameVnode (a, b) {// 判斷兩個VNode節(jié)點是否是同一個節(jié)點
  return (
    a.key === b.key && // key相同
    (
      a.tag === b.tag && // tag相同
      a.isComment === b.isComment && // 注釋節(jié)點標識相同
      isDef(a.data) === isDef(b.data) && // data值狀態(tài)相同
      sameInputType(a, b) // input的type相同
    )
  )
}

function patch (oldVnode, vnode, hydrating, removeOnly) {
  if (isUndef(vnode)) {
   if (isDef(oldVnode)) { invokeDestroyHook(oldVnode); }
   return
  }
  ...
  if (isUndef(oldVnode)) {
   isInitialPatch = true;// 組件初始加載
   createElm(vnode, insertedVnodeQueue);
  } else {
   var isRealElement = isDef(oldVnode.nodeType);
   if (!isRealElement && sameVnode(oldVnode, vnode)) {
    patchVnode(oldVnode, vnode, insertedVnodeQueue, null, null, removeOnly);
   } else {
    ...
    var oldElm = oldVnode.elm;
    var parentElm = nodeOps.parentNode(oldElm);// 獲取父元素
    // create new node
    createElm(
     vnode,
     insertedVnodeQueue,
     oldElm._leaveCb ? null : parentElm,
     nodeOps.nextSibling(oldElm)// 獲取緊跟的弟弟元素
    );
    if (isDef(parentElm)) {
     removeVnodes(parentElm, [oldVnode], 0, 0);// 銷毀舊節(jié)點以及DOM元素
    } else if (isDef(oldVnode.tag)) {
     invokeDestroyHook(oldVnode);
    }
   }
  }
  invokeInsertHook(vnode, insertedVnodeQueue, isInitialPatch);
  return vnode.elm
 }
}

 function patchVnode (
  oldVnode,
  vnode,
  insertedVnodeQueue,
  ownerArray,
  index,
  removeOnly
 ) {
  if (oldVnode === vnode) {
   return
  }
  ...
  if (isUndef(vnode.text)) {
   if (isDef(oldCh) && isDef(ch)) {
    if (oldCh !== ch) { updateChildren(elm, oldCh, ch, insertedVnodeQueue, removeOnly); }
   } else if (isDef(ch)) {
    if (process.env.NODE_ENV !== 'production') {
     checkDuplicateKeys(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);
  }
  ...
 }

  var oldStartIdx = 0;// 表示當前正在處理的舊起始節(jié)點序號
  var newStartIdx = 0;// 表示當前正在處理的新起始節(jié)點序號
  var oldEndIdx = oldCh.length - 1;// 表示當前正在處理的舊結(jié)尾節(jié)點序號
  var oldStartVnode = oldCh[0];// 表示當前正在處理的舊起始節(jié)點
  var oldEndVnode = oldCh[oldEndIdx];// 表示當前正在處理的舊結(jié)尾節(jié)點
  var newEndIdx = newCh.length - 1;// 表示當前正在處理的新結(jié)尾節(jié)點序號
  var newStartVnode = newCh[0];// 表示當前正在處理的新起始節(jié)點
  var newEndVnode = newCh[newEndIdx];// 表示當前正在處理的新結(jié)尾節(jié)點
  var oldKeyToIdx, // 尚未處理的舊節(jié)點key值映射
    idxInOld, // 與新節(jié)點key值相同的舊節(jié)點序號
    vnodeToMove, // 與新節(jié)點key值相同的舊節(jié)點
    refElm;// 指向當前正在處理的新結(jié)尾節(jié)點的后一個節(jié)點（已處理）的DOM元素

function updateChildren (parentElm, oldCh, newCh, insertedVnodeQueue, removeOnly) {
  var oldStartIdx = 0;// 表示當前正在處理的舊起始節(jié)點序號
  var newStartIdx = 0;// 表示當前正在處理的新起始節(jié)點序號
  var oldEndIdx = oldCh.length - 1;// 表示當前正在處理的舊結(jié)尾節(jié)點序號
  var oldStartVnode = oldCh[0];// 表示當前正在處理的舊起始節(jié)點
  var oldEndVnode = oldCh[oldEndIdx];// 表示當前正在處理的舊結(jié)尾節(jié)點
  var newEndIdx = newCh.length - 1;// 表示當前正在處理的新結(jié)尾節(jié)點序號
  var newStartVnode = newCh[0];// 表示當前正在處理的新起始節(jié)點
  var newEndVnode = newCh[newEndIdx];// 表示當前正在處理的新結(jié)尾節(jié)點
  var oldKeyToIdx, idxInOld, vnodeToMove, refElm;
  ...
  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, newCh, newStartIdx);
    oldStartVnode = oldCh[++oldStartIdx];
    newStartVnode = newCh[++newStartIdx];
   } else if (sameVnode(oldEndVnode, newEndVnode)) {
    patchVnode(oldEndVnode, newEndVnode, insertedVnodeQueue, newCh, newEndIdx);
    oldEndVnode = oldCh[--oldEndIdx];
    newEndVnode = newCh[--newEndIdx];
   } else if (sameVnode(oldStartVnode, newEndVnode)) { // Vnode moved right
    patchVnode(oldStartVnode, newEndVnode, insertedVnodeQueue, newCh, newEndIdx);
    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, newCh, newStartIdx);
    canMove && nodeOps.insertBefore(parentElm, oldEndVnode.elm, oldStartVnode.elm);
    oldEndVnode = oldCh[--oldEndIdx];
    newStartVnode = newCh[++newStartIdx];
   } else {
    if (isUndef(oldKeyToIdx)) { oldKeyToIdx = createKeyToOldIdx(oldCh, oldStartIdx, oldEndIdx); }// 緩存尚未處理的舊節(jié)點key值
    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, newCh, newStartIdx);
      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);
  }
 }