模板tamplate通过parse，optimize，generate等一些列操作之后，把AST转为render function code进而生成虚构VNode,模板编译阶段根本曾经实现了，那么这一章，咱们来探讨一下Vue中的一个算法策略–dom diff 首先来介绍下什么叫dom diff
什么是虚构dom
咱们通过后面的章节学习曾经晓得，要晓得渲染实在DOM的开销是很大的，比方有时候咱们批改了某个数据，如果间接渲染到实在dom上会引起整个dom树的重绘和重排，有没有可能咱们只更新咱们批改的那一小块dom而不要更新整个dom呢？
为了解决这个问题，咱们的解决方案是–依据实在DOM生成一颗virtual DOM，当virtual DOM某个节点的数据扭转后会生成一个新的Vnode，而后Vnode和oldVnode作比照，发现有不一样的中央就间接批改在实在的DOM上，而后使oldVnode的值为Vnode。这也就是咱们所说的一个虚构dom diff的过程
图示
传统的Diff算法所消耗的工夫复杂度为O(n^3),那么这个O(n^3)是怎么算进去的？
- 传统diff算法工夫复杂度为n(第一次Old与新的所有节点比照)—-
O(n) - 传统diff算法工夫复杂度为n(第二次Old树的所有节点与新的所有节点比照)—-
O(n^2) - 新树的生成，节点可变编辑，工夫复杂度为n(遍历以后树)—-
O(n^3)
第一次比照 (1:n)
第二次比照 (1:n)
第n次比照 (n:n)
到这里那么n个节点与n个节点暴力比照就比照完了，那么就开启第三轮可编辑树节点遍历，更改之后的树由vdom(old)到vdom(new)
故而传统diff算法O(n^3)是这么算进去的,然而这不是咱们明天钻研的重点。
古代diff算法
古代diff算法策略说的是，同层级比拟，广度优先
那么这里的话咱们要深刻源码了，在深刻源码之前咱们在心中应该造成这样一个概念，整个diff的流程是什么？咱们再比照着源码解读
diff算法流程图
深刻源码
咱们在Vue初始化的时候调用lifecycleMixin函数的时候，会给Vue的原型上挂载_update办法
_update
Vue.prototype._update = function (vnode: VNode, hydrating?: boolean) {
const vm: Component = this
if (vm._isMounted) {
//会调用申明周期中的beforeUpdate回调函数
callHook(vm, 'beforeUpdate')
}
const prevEl = vm.$el
const prevVnode = vm._vnode
const prevActiveInstance = activeInstance
activeInstance = vm
vm._vnode = vnode
// Vue.prototype.__patch__ is injected in entry points
// based on the rendering backend used.
//若组件自身的vnode未生成,间接用传入的vnode生成dom
if (!prevVnode) {
// initial render
vm.$el = vm.__patch__(
vm.$el, vnode, hydrating, false /* removeOnly */,
vm.$options._parentElm,
vm.$options._refElm
)
// no need for the ref nodes after initial patch
// this prevents keeping a detached DOM tree in memory (#5851)
vm.$options._parentElm = vm.$options._refElm = null
} else {
//对新旧vnode进行diff
// updates
vm.$el = vm.__patch__(prevVnode, vnode)
}
activeInstance = prevActiveInstance
// update __vue__ reference
if (prevEl) {
prevEl.__vue__ = null
}
if (vm.$el) {
vm.$el.__vue__ = vm
}
// if parent is an HOC, update its $el as well
if (vm.$vnode && vm.$parent && vm.$vnode === vm.$parent._vnode) {
vm.$parent.$el = vm.$el
}
咱们在这里能够看到vm.$el = vm.__patch__办法，追根溯源_patch_的定义：
Vue.prototype.__patch__ = inBrowser ? patch : noop
可见这里是一个浏览器环境的甄别，如果在浏览器环境中，咱们会执行patch，不在的话会执行noop，这是一个util外面的一个办法，用来跨平台的，咱们这里临时不思考，接着咱们去看patch的具体实现./patch文件，参考vue实战视频解说：进入学习
import * as nodeOps from 'web/runtime/node-ops'
import { createPatchFunction } from 'core/vdom/patch'
import baseModules from 'core/vdom/modules/index'
import platformModules from 'web/runtime/modules/index'
const modules = platformModules.concat(baseModules)
export const patch: Function = createPatchFunction({ nodeOps, modules })
createPatchFunction函数
/** * 创立patch办法 */
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)
}
/** * 创立一个回调办法, 用于删除节点 * * */
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)
}
}
/** * 通过vnode的tag判断是否是原生dom标签或者组件标签 * 用于创立实在DOM节点时, 预先判断tag的合法性 */
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
// 创立一个节点
function createElm (
vnode,
insertedVnodeQueue,
parentElm,
refElm,
nested,
ownerArray,
index
) {
// 节点曾经被渲染, 须要应用一个克隆节点
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)
}
// 创立组件节点 详见本文件中的createComponent办法
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
/** * 如果要创立的节点有tag属性, 这里做一下校验 * 如果该节点下面有v-pre指令, 间接给flag加1 * 如果没有v-pre须要调用isUnknownElement判断标签是否非法, 而后给出正告 */
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)
}
}
/** * 创立组件 * 如果组件实例曾经存在, 只须要初始化组件并从新激活组件即可 */
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 */, parentElm, refElm)
}
// 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)
if (isTrue(isReactivated)) {
reactivateComponent(vnode, insertedVnodeQueue, parentElm, refElm)
}
return true
}
}
}
/** * 初始化组件 * 次要的操作是已插入的vnode队列, 触发create钩子, 设置style的scope, 注册ref */
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)
}
}
/** * 激活组件 */
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)
}
/** * 插入节点, 有父节点的插入到后面, 没有的插入到前面 */
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)
}
}
// 递归调用销毁钩子
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])
}
}
}
/** * 删除多个节点 * 文本节点能够间接删除, 其余节点须要触发两个钩子 */
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)
}
}
// diff操作外围算法
function updateChildren (parentElm, oldCh, newCh, insertedVnodeQueue, removeOnly) {
// 记录新旧节点列表的首尾元素 用于比拟
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
// 在transition中 不能挪动节点
const canMove = !removeOnly
// 查看是否有反复的key
if (process.env.NODE_ENV !== 'production') {
checkDuplicateKeys(newCh)
}
// 一共分四种状况探讨, 旧列表第一个与新列表第一个比照, 旧列表最初一个与新列表最初一个比照
// 而后新列表第一个和旧列表最初一个比照, 新列表最初一个和旧列表第一个比照
// 之所以要穿插头尾比照, 是为了避免最差的状况呈现
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 {
// 以上四种状况都不满足时, 应用新列表第一个vdom的key去旧列表查找
// 如果能够找到key雷同的元素, 间接进行patch而后进入下一次循环
// 找不到则插入一个新节点
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]
}
}
// 新旧列表其中之一全副循环实现后, 开始清理残余的节点
// 如果旧列表全副遍历实现, 新列表还有残余, 间接创立这些新节点
// 反之, 如果新列表全副遍历, 旧列表还有残余, 间接删除这些旧节点
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)
}
}
/** * 查看是否有反复的key * 一个很简略的遍历查找反复值的操作 * 其实这个seenKeys我感觉改成数组会更好, 写成object又给每个key的value置为true蛮奇怪的 */
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
}
}
}
}
/** * 在旧的子节点列表寻找类似节点(只查找第一个) */
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) {
// 如果oldVnode跟vnode完全一致，那么不须要做任何事件
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
}
// 如果oldVnode跟vnode都是动态节点，且具备雷同的key
// 当vnode是克隆节点或是v-once指令管制的节点时
// 只须要把oldVnode.elm和oldVnode.child都复制到vnode上，也不必再有其余操作
// 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)
}
// 如果vnode不是文本节点或正文节点
if (isUndef(vnode.text)) {
// 如果oldVnode和vnode都有子节点，且2方的子节点不完全一致，就执行updateChildren
if (isDef(oldCh) && isDef(ch)) {
if (oldCh !== ch) updateChildren(elm, oldCh, ch, insertedVnodeQueue, removeOnly)
} else if (isDef(ch)) {
// 如果只有vnode有子节点，那就创立这些子节点
if (isDef(oldVnode.text)) nodeOps.setTextContent(elm, '')
addVnodes(elm, null, ch, 0, ch.length - 1, insertedVnodeQueue)
// 如果只有oldVnode有子节点，那就把这些节点都删除
} else if (isDef(oldCh)) {
removeVnodes(elm, oldCh, 0, oldCh.length - 1)
// 如果oldVnode和vnode都没有子节点，然而oldVnode是文本节点或正文节点，就把vnode.elm的文本设置为空字符串
} else if (isDef(oldVnode.text)) {
nodeOps.setTextContent(elm, '')
}
// 如果vnode是文本节点或正文节点，然而vnode.text != oldVnode.text时，只须要更新vnode.elm的文本内容即可
} 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)
}
}
/** * 这里返回一个patch函数供后续对vnode进行patch操作 * 这里的patch操作是指, 将oldVnode对应的实在DOM更改为vnode对应的实在DOM, 所须要的最低性能开销的操作(或者说是较低) * 参数中的oldVnode是更新前的旧节点, vnode是将要更新的新节点, hydrating是一个flag标识是否与原生DOM混合, removeOnly是在过渡动画中应用 */
return function patch (oldVnode, vnode, hydrating, removeOnly, parentElm, refElm) {
// 这里很简略, 如果新节点不存在, 旧节点也不存在, 无需任何操作, 如果新节点不存在,但旧节点存在, 阐明须要删除旧节点, 调用一个销毁钩子
if (isUndef(vnode)) {
if (isDef(oldVnode)) invokeDestroyHook(oldVnode)
return
}
// 用于标识是否初始化这个节点
let isInitialPatch = false
const insertedVnodeQueue = []
// 旧节点不存在 阐明须要创立一个新节点
if (isUndef(oldVnode)) {
// empty mount (likely as component), create new root element
isInitialPatch = true
createElm(vnode, insertedVnodeQueue, parentElm, refElm)
} else {
// 走到这里 阐明新旧节点都存在, 这时比较复杂, 分几种状况解决
// 先通过nodeType判断是否是真正的节点, 真正的节点nodeType取值范畴是1~12
// vue里罕用的根本只有三种 1代表是dom元素节点 3是文本节点 8是正文节点
const isRealElement = isDef(oldVnode.nodeType)
if (!isRealElement && sameVnode(oldVnode, vnode)) {
// patch existing root node
// 惯例状况下, 新旧节点是类似节点, 对新旧节点做具体的比照操作
patchVnode(oldVnode, vnode, insertedVnodeQueue, removeOnly)
} else {
if (isRealElement) {
// 当新旧节点不是类似节点, 旧节点是一个实在节点时
// mounting to a real element
// check if this is server-rendered content and if we can perform
// a successful hydration.
// 服务端渲染非凡解决
if (oldVnode.nodeType === 1 && oldVnode.hasAttribute(SSR_ATTR)) {
oldVnode.removeAttribute(SSR_ATTR)
hydrating = true
}
// 须要用hydrate函数将虚构DOM和实在DOM进行映射
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
}
}
能够看到patch接管的参数
oldVnode：旧的虚构节点vnode：新的虚构节点hydrating：是否映射removeOnly：标识parentElm：父节点refElm：被插入之后的占位符
那么外围diff代码在于 sameVnode、createElm、patchVNode咱们顺次开展来说
sameVnode
顾名思义能够看判断两个节点是不是同一个节点
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)
)
)
)
}
/** * 节点 key 必须雷同 * tag、正文、data是否存在、input类型是否雷同 * 如果isAsyncPlaceholder是true，则须要asyncFactory属性雷同 */
createElm
// 创立一个节点
function createElm (
vnode,
insertedVnodeQueue,
parentElm,
refElm,
nested,
ownerArray,
index
) {
// 节点曾经被渲染, 须要应用一个克隆节点
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)
}
// 创立组件节点 详见本文件中的createComponent办法
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
/** * 如果要创立的节点有tag属性, 这里做一下校验 * 如果该节点下面有v-pre指令, 间接给flag加1 * 如果没有v-pre须要调用isUnknownElement判断标签是否非法, 而后给出正告 */
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)
}
}
此段代码就是创立实在dom的目标，下一章谈判到。
patchVnode
function patchVnode (oldVnode, vnode, insertedVnodeQueue, removeOnly) {
// 如果oldVnode跟vnode完全一致，那么不须要做任何事件
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
}
// 如果oldVnode跟vnode都是动态节点，且具备雷同的key
// 当vnode是克隆节点或是v-once指令管制的节点时
// 只须要把oldVnode.elm和oldVnode.child都复制到vnode上，也不必再有其余操作
// 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)
}
// 如果vnode不是文本节点或正文节点
if (isUndef(vnode.text)) {
// 如果oldVnode和vnode都有子节点，且2方的子节点不完全一致，就执行updateChildren
if (isDef(oldCh) && isDef(ch)) {
if (oldCh !== ch) updateChildren(elm, oldCh, ch, insertedVnodeQueue, removeOnly)
} else if (isDef(ch)) {
// 如果只有vnode有子节点，那就创立这些子节点
if (isDef(oldVnode.text)) nodeOps.setTextContent(elm, '')
addVnodes(elm, null, ch, 0, ch.length - 1, insertedVnodeQueue)
// 如果只有oldVnode有子节点，那就把这些节点都删除
} else if (isDef(oldCh)) {
removeVnodes(elm, oldCh, 0, oldCh.length - 1)
// 如果oldVnode和vnode都没有子节点，然而oldVnode是文本节点或正文节点，就把vnode.elm的文本设置为空字符串
} else if (isDef(oldVnode.text)) {
nodeOps.setTextContent(elm, '')
}
// 如果vnode是文本节点或正文节点，然而vnode.text != oldVnode.text时，只须要更新vnode.elm的文本内容即可
} 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)
}
}
具体代码性能曾经解释的很分明了，这里的addVnodes和removeVnodes就是新增与移除虚构节点，外围代码咱们次要关注一个updateChildren
updateChildren
// diff操作外围算法
function updateChildren (parentElm, oldCh, newCh, insertedVnodeQueue, removeOnly) {
// 记录新旧节点列表的首尾元素 用于比拟
let oldStartIdx = 0 // 旧列表终点地位
let newStartIdx = 0 // 新列表终点地位
let oldEndIdx = oldCh.length - 1 // 旧列表起点地位
let oldStartVnode = oldCh[0] // 旧列表终点值
let oldEndVnode = oldCh[oldEndIdx] // 旧列表起点值
let newEndIdx = newCh.length - 1 // 新列表起点地位
let newStartVnode = newCh[0] // 新列表终点值
let newEndVnode = newCh[newEndIdx] // 新列表起点值
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
// 在transition中 不能挪动节点
const canMove = !removeOnly
// 查看是否有反复的key
if (process.env.NODE_ENV !== 'production') {
checkDuplicateKeys(newCh)
}
// 一共分四种状况探讨, 旧列表第一个与新列表第一个比照, 旧列表最初一个与新列表最初一个比照
// 而后新列表第一个和旧列表最初一个比照, 新列表最初一个和旧列表第一个比照
// 之所以要穿插头尾比照, 是为了避免最差的状况呈现
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 {
// 以上四种状况都不满足时, 应用新列表第一个vdom的key去旧列表查找
// 如果能够找到key雷同的元素, 间接进行patch而后进入下一次循环
// 找不到则插入一个新节点
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]
}
}
// 新旧列表其中之一全副循环实现后, 开始清理残余的节点
// 如果旧列表全副遍历实现, 新列表还有残余, 间接创立这些新节点
// 反之, 如果新列表全副遍历, 旧列表还有残余, 间接删除这些旧节点
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)
}
}
这里利用了while循环与双指针比照新旧虚构dom
定义指针变量
let oldStartIdx = 0 // 旧列表终点地位
let newStartIdx = 0 // 新列表终点地位
let oldEndIdx = oldCh.length - 1 // 旧列表起点地位
let oldStartVnode = oldCh[0] // 旧列表终点值
let oldEndVnode = oldCh[oldEndIdx] // 旧列表起点值
let newEndIdx = newCh.length - 1 // 新列表起点地位
let newStartVnode = newCh[0] // 新列表终点值
let newEndVnode = newCh[newEndIdx] // 新列表起点值
定义循环
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 {
// 以上四种状况都不满足时, 应用新列表第一个vdom的key去旧列表查找
// 如果能够找到key雷同的元素, 间接进行patch而后进入下一次循环
// 找不到则插入一个新节点
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]
}
}
检测oldStartVnode、oldEndVnode
if (isUndef(oldStartVnode)) {
oldStartVnode = oldCh[++oldStartIdx]
} else if (isUndef(oldEndVnode)) {
oldEndVnode = oldCh[--oldEndIdx]
}
如果oldStartVnode不存在，oldCh起始点向后挪动。如果oldEndVnode不存在，oldCh终止点向前挪动。
oldStartVnode 和 newStartVnode 是雷同节点
else if (sameVnode(oldStartVnode, newStartVnode)) {
patchVnode(oldStartVnode, newStartVnode, insertedVnodeQueue)
oldStartVnode = oldCh[++oldStartIdx]
newStartVnode = newCh[++newStartIdx]
}
如果oldStartVnode 和 newStartVnode 是雷同节点，则patchVnode，同时彼此向后挪动一位
oldEndVnode 和 newEndVnode 是雷同节点
else if (sameVnode(oldEndVnode, newEndVnode)) {
patchVnode(oldEndVnode, newEndVnode, insertedVnodeQueue)
oldEndVnode = oldCh[--oldEndIdx]
newEndVnode = newCh[--newEndIdx]
}
如果oldEndVnode 和 newEndVnode 是雷同节点，则patchVnode，同时彼此向前挪动一位
oldStartVnode 和 newEndVnode 是雷同节点
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]
}
如果oldStartVnode 和 newEndVnode 是雷同节点，则先 patchVnode，而后把oldStartVnode移到oldCh最初的地位即可，而后oldStartIdx向后挪动一位，newEndIdx向前挪动一位
oldEndVnode 和 newStartVnode 是雷同节点
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]
}
如果oldEndVnode 和 newStartVnode 是雷同节点，则先 patchVnode，而后把oldEndVnode移到oldCh最前的地位即可，而后newStartIdx向后挪动一位，oldEndIdx向前挪动一位
key不雷同执行createElm办法
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)
}
如果以上条件都不匹配，则查找oldVnode中与vnode具备雷同key的节点，并将查找的后果赋值给elmToMove。如果找不到雷同key的节点，则示意是新创建的节点
key雷同，就认为是同一节点
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)
}
newStartVnode = newCh[++newStartIdx]
若为同一类型就调用patchVnode，就将对应下标处的oldVnode设置为undefined，把vnodeToMove插入到oldCh之前，newStartIdx持续向后挪动。如果两个 vnode 不雷同，视为新元素，执行 createElm创立。
如果老dom的开始索引大于完结索引，新dom数组大于老dom数组，示意新增会调用addVnodes办法
if (oldStartIdx > oldEndIdx) {
refElm = isUndef(newCh[newEndIdx + 1]) ? null : newCh[newEndIdx + 1].elm
addVnodes(parentElm, refElm, newCh, newStartIdx, newEndIdx, insertedVnodeQueue)
}
如果老dom的开始索引小于完结索引，新dom数组小于老dom数组，示意新增会调用removeVnodes办法
else if (newStartIdx > newEndIdx) {
removeVnodes(parentElm, oldCh, oldStartIdx, oldEndIdx)
}
总结
因为古代diff算法策略是同层级比拟，广度优先，故而古代算法复杂度为O(n) 这一章咱们讲述了传统diff算法复杂度,O(n^3)到古代的O(n)的实现的一个思路，下一章就开始解说比照过后的vdom如何映射成实在dom
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