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前言
DOM“天生就慢”，所以前端各大框架都提供了对DOM操作进行优化的办法
Angular中的是脏值检查
React首先提出了Virtual Dom，
Vue2.0也加入了Virtual Dom，与React类似。
Diff算法的作用是用来计算出 Virtual DOM 中被改变的部分，然后针对该部分进行原生DOM操作，而不用重新渲染整个页面。
Diff算法有三大策略：
Tree Diff
Component Diff
Element Diff
三种策略的执行顺序也是顺序依次执行。
Tree Diff 是对树每一层进行遍历，找出不同
Component Diff 是数据层面的差异比较
如果都是同一类型的组件(即：两节点是同一个组件类的两个不同实例，比如：
与 )，按照原策略继续比较Virtual DOM树即可
如果出现不是同一类型的组件，则将该组件判断为dirty component，从而替换整个组件下的所有子节点
Element Diff真实DOM渲染，结构差异的比较
首先进行第一层比较，第一层都是R，不发生变化；然后进入第二层Component Diff，发现A组件没有，则删除A及其子组件B、C；最后比较第三层，创建A及其子组件B、C。
当节点处于同一层级时，Diff提供三种DOM操作：删除、移动、插入。
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首先将OldVnode 和 NewVnode的首尾位置分别标记为oldS、oldE、newS、newE。
oldS和newS相同，不发生变化，oldS++，newS++
oldS = a，oldE = d
newS = a, newE = c
newS与OldVnode不匹配，oldS前面插入f，newS++
oldS = b，oldE = d
newS = f， newE = c
newS与oldE相同，oldE移动到oldS前面，newS++，oldE--
oldS = b，oldE = d
newS = d， newE = c
newE与oldE相同，不发生变化，newE--，oldE--
oldS = b，oldE = c
newS = e， newE = c
都不相同，
oldS前插入newE，删除oldS，oldS++，newS++，newE--，oldE--
oldS = b，oldE = b
newS = e， newE = e
oldS > oldE，Diff结束，最后结果为：a、f、d、e、c
下面对于Vue 2.X版本中使用的Virtual Dom进行分析。
updataChildren是Diff算法的核心，所以本文对updataChildren进行了图文的分析。
VNode对象
一个VNode的实例包含了以下属性，这部分代码在src/core/vdom/vnode.js里
export default class VNode {
tag: string | void;
data: VNodeData | void;
children: ?Array<VNode>;
text: string | void;
elm: Node | void;
ns: string | void;
context: Component | void; // rendered in this component's scope
key: string | number | void;
componentOptions: VNodeComponentOptions | void;
componentInstance: Component | void; // component instance
parent: VNode | void; // component placeholder node
// strictly internal
raw: boolean; // contains raw HTML? (server only)
isStatic: boolean; // hoisted static node
isRootInsert: boolean; // necessary for enter transition check
isComment: boolean; // empty comment placeholder?
isCloned: boolean; // is a cloned node?
isOnce: boolean; // is a v-once node?
asyncFactory: Function | void; // async component factory function
asyncMeta: Object | void;
isAsyncPlaceholder: boolean;
ssrContext: Object | void;
fnContext: Component | void; // real context vm for functional nodes
fnOptions: ?ComponentOptions; // for SSR caching
devtoolsMeta: ?Object; // used to store functional render context for devtools
fnScopeId: ?string; // functional scope id support
constructor (
tag?: string,
data?: VNodeData,
children?: ?Array<VNode>,
text?: string,
elm?: Node,
context?: Component,
componentOptions?: VNodeComponentOptions,
asyncFactory?: Function
) {
this.tag = tag
this.data = data
this.children = children
this.text = text
this.elm = elm
this.ns = undefined
this.context = context
this.fnContext = undefined
this.fnOptions = undefined
this.fnScopeId = undefined
this.key = data && data.key
this.componentOptions = componentOptions
this.componentInstance = undefined
this.parent = undefined
this.raw = false
this.isStatic = false
this.isRootInsert = true
this.isComment = false
this.isCloned = false
this.isOnce = false
this.asyncFactory = asyncFactory
this.asyncMeta = undefined
this.isAsyncPlaceholder = false
}
// DEPRECATED: alias for componentInstance for backwards compat.
/* istanbul ignore next */
get child (): Component | void {
return this.componentInstance
}
}
export const createEmptyVNode = (text: string = '') => {
const node = new VNode()
node.text = text
node.isComment = true
return node
}
export function createTextVNode (val: string | number) {
return new VNode(undefined, undefined, undefined, String(val))
}
// optimized shallow clone
// used for static nodes and slot nodes because they may be reused across
// multiple renders, cloning them avoids errors when DOM manipulations rely
// on their elm reference.
export function cloneVNode (vnode: VNode): VNode {
const cloned = new VNode(
vnode.tag,
vnode.data,
// #7975
// clone children array to avoid mutating original in case of cloning
// a child.
vnode.children && vnode.children.slice(),
vnode.text,
vnode.elm,
vnode.context,
vnode.componentOptions,
vnode.asyncFactory
)
cloned.ns = vnode.ns
cloned.isStatic = vnode.isStatic
cloned.key = vnode.key
cloned.isComment = vnode.isComment
cloned.fnContext = vnode.fnContext
cloned.fnOptions = vnode.fnOptions
cloned.fnScopeId = vnode.fnScopeId
cloned.asyncMeta = vnode.asyncMeta
cloned.isCloned = true
return cloned
}
注释
`tag`: 当前节点的标签名
`data`: 当前节点的数据对象，具体包含哪些字段可以参考vue源码types/vnode.d.ts中对VNodeData的定义
`children`: 数组类型，包含了当前节点的子节点
`text`: 当前节点的文本，一般文本节点或注释节点会有该属性
`elm`: 当前虚拟节点对应的真实的dom节点
`ns`: 节点的namespace
`context`: 编译作用域
`functionalContext`: 函数化组件的作用域
`key`: 节点的key属性，用于作为节点的标识，有利于patch的优化
`componentOptions`: 创建组件实例时会用到的选项信息
`child`: 当前节点对应的组件实例
`parent`: 组件的占位节点
`raw`: raw html
`isStatic`: 静态节点的标识
`isRootInsert`: 是否作为根节点插入，被包裹的节点，该属性的值为false
`isComment`: 当前节点是否是注释节点
`isCloned`: 当前节点是否为克隆节点
`isOnce`: 当前节点是否有v-once指令
VNode的分类:
可以理解为VueVirtual Dom的一个基类，通过VNode构造函数生成的VNnode实例可为如下几类
`EmptyVNode`: 没有内容的注释节点
`TextVNode`: 文本节点
`ElementVNode`: 普通元素节点
`ComponentVNode`: 组件节点
`CloneVNode`: 克隆节点，可以是以上任意类型的节点，唯一的区别在于isCloned属性为true
Create-Element源码解析
这部分代码在src/core/vdom/create-element.js里，我就直接粘代码加上我的注释了
import config from '../config'
import VNode, { createEmptyVNode } from './vnode'
import { createComponent } from './create-component'
import { traverse } from '../observer/traverse'
import {
warn,
isDef,
isUndef,
isTrue,
isObject,
isPrimitive,
resolveAsset
} from '../util/index'
import {
normalizeChildren,
simpleNormalizeChildren
} from './helpers/index'
const SIMPLE_NORMALIZE = 1
const ALWAYS_NORMALIZE = 2
// wrapper function for providing a more flexible interface
// without getting yelled at by flow
export function createElement (
context: Component,
tag: any,
data: any,
children: any,
normalizationType: any,
alwaysNormalize: boolean
): VNode | Array<VNode> {
if (Array.isArray(data) || isPrimitive(data)) {
normalizationType = children
children = data
data = undefined
}
if (isTrue(alwaysNormalize)) {
normalizationType = ALWAYS_NORMALIZE
}
return _createElement(context, tag, data, children, normalizationType)
}
export function _createElement (
context: Component,
tag?: string | Class<Component> | Function | Object,
data?: VNodeData,
children?: any,
normalizationType?: number
): VNode | Array<VNode> {
if (isDef(data) && isDef((data: any).__ob__)) {
process.env.NODE_ENV !== 'production' && warn(
`Avoid using observed data object as vnode data: ${JSON.stringify(data)}\n` +
'Always create fresh vnode data objects in each render!',
context
)
return createEmptyVNode()
}
// object syntax in v-bind
if (isDef(data) && isDef(data.is)) {
tag = data.is
}
if (!tag) {
// in case of component :is set to falsy value
return createEmptyVNode()
}
// warn against non-primitive key
if (process.env.NODE_ENV !== 'production' &&
isDef(data) && isDef(data.key) && !isPrimitive(data.key)
) {
if (!__WEEX__ || !('@binding' in data.key)) {
warn(
'Avoid using non-primitive value as key, ' +
'use string/number value instead.',
context
)
}
}
// support single function children as default scoped slot
if (Array.isArray(children) &&
typeof children[0] === 'function'
) {
data = data || {}
data.scopedSlots = { default: children[0] }
children.length = 0
}
if (normalizationType === ALWAYS_NORMALIZE) {
children = normalizeChildren(children)
} else if (normalizationType === SIMPLE_NORMALIZE) {
children = simpleNormalizeChildren(children)
}
let vnode, ns
if (typeof tag === 'string') {
let Ctor
ns = (context.$vnode && context.$vnode.ns) || config.getTagNamespace(tag)
if (config.isReservedTag(tag)) {
// platform built-in elements
if (process.env.NODE_ENV !== 'production' && isDef(data) && isDef(data.nativeOn)) {
warn(
`The .native modifier for v-on is only valid on components but it was used on <${tag}>.`,
context
)
}
vnode = new VNode(
config.parsePlatformTagName(tag), data, children,
undefined, undefined, context
)
} else if ((!data || !data.pre) && isDef(Ctor = resolveAsset(context.$options, 'components', tag))) {
// component
vnode = createComponent(Ctor, data, context, children, tag)
} else {
// unknown or unlisted namespaced elements
// check at runtime because it may get assigned a namespace when its
// parent normalizes children
vnode = new VNode(
tag, data, children,
undefined, undefined, context
)
}
} else {
// direct component options / constructor
vnode = createComponent(tag, data, context, children)
}
if (Array.isArray(vnode)) {
return vnode
} else if (isDef(vnode)) {
if (isDef(ns)) applyNS(vnode, ns)
if (isDef(data)) registerDeepBindings(data)
return vnode
} else {
return createEmptyVNode()
}
}
function applyNS (vnode, ns, force) {
vnode.ns = ns
if (vnode.tag === 'foreignObject') {
// use default namespace inside foreignObject
ns = undefined
force = true
}
if (isDef(vnode.children)) {
for (let i = 0, l = vnode.children.length; i < l; i++) {
const child = vnode.children[i]
if (isDef(child.tag) && (
isUndef(child.ns) || (isTrue(force) && child.tag !== 'svg'))) {
applyNS(child, ns, force)
}
}
}
}
// ref #5318
// necessary to ensure parent re-render when deep bindings like :style and
// :class are used on slot nodes
function registerDeepBindings (data) {
if (isObject(data.style)) {
traverse(data.style)
}
if (isObject(data.class)) {
traverse(data.class)
}
}
Patch原理
patch函数的定义在src/core/vdom/patch.js中，patch逻辑比较简单，就不粘代码了
patch函数接收6个参数：
`oldVnode`: 旧的虚拟节点或旧的真实dom节点
`vnode`: 新的虚拟节点
`hydrating`: 是否要跟真是dom混合
`removeOnly`: 特殊flag，用于组件
`parentElm`: 父节点
`refElm`: 新节点将插入到refElm之前
patch的逻辑是：
if vnode不存在但是oldVnode存在，说明意图是要销毁老节点，那么就调用invokeDestroyHook(oldVnode)来进行销
if oldVnode不存在但是vnode存在，说明意图是要创建新节点，那么就调用createElm来创建新节点
else 当vnode和oldVnode都存在时
if oldVnode和vnode是同一个节点，就调用patchVnode来进行patch
当vnode和oldVnode不是同一个节点时，如果oldVnode是真实dom节点或hydrating设置为true，需要用hydrate函数将虚拟dom和真是dom进行映射，然后将oldVnode设置为对应的虚拟dom，找到oldVnode.elm的父节点，根据vnode创建一个真实dom节点并插入到该父节点中oldVnode.elm的位置
patchVnode的逻辑是：
如果oldVnode跟vnode完全一致，那么不需要做任何事情
如果oldVnode跟vnode都是静态节点，且具有相同的key，当vnode是克隆节点或是v-once指令控制的节点时，只需要把oldVnode.elm和oldVnode.child都复制到vnode上，也不用再有其他操作
否则，如果vnode不是文本节点或注释节点
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
如果只有oldVnode有子节点，那就把这些节点都删除
如果只有vnode有子节点，那就创建这些子节点
如果oldVnode和vnode都没有子节点，但是oldVnode是文本节点或注释节点，就把vnode.elm的文本设置为空字符串
如果vnode是文本节点或注释节点，但是vnode.text != oldVnode.text时，只需要更新vnode.elm的文本内容就可以
代码如下：
**
* 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 (nodeOps.parentNode(ref) === 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 (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, 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)
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(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,
ownerArray,
index,
removeOnly
) {
if (oldVnode === vnode) {
return
}
if (isDef(vnode.elm) && isDef(ownerArray)) {
// clone reused vnode
vnode = ownerArray[index] = cloneVNode(vnode)
}
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 (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(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, null, null, 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([oldVnode], 0, 0)
} else if (isDef(oldVnode.tag)) {
invokeDestroyHook(oldVnode)
}
}
}
invokeInsertHook(vnode, insertedVnodeQueue, isInitialPatch)
return vnode.elm
}
}
updataChildren原理
updateChildren的逻辑是：
分别获取oldVnode和vnode的firstChild、lastChild，赋值给oldStartVnode、oldEndVnode、newStartVnode、newEndVnode
如果oldStartVnode和newStartVnode是同一节点，调用patchVnode进行patch，然后将oldStartVnode和newStartVnode都设置为下一个子节点，重复上述流程
如果oldEndVnode和newEndVnode是同一节点，调用patchVnode进行patch，然后将oldEndVnode和newEndVnode都设置为上一个子节点，重复上述流程
如果oldStartVnode和newEndVnode是同一节点，调用patchVnode进行patch，如果removeOnly是false，那么可以把oldStartVnode.elm移动到oldEndVnode.elm之后，然后把oldStartVnode设置为下一个节点，newEndVnode设置为上一个节点，重复上述流程
如果newStartVnode和oldEndVnode是同一节点，调用patchVnode进行patch，如果removeOnly是false，那么可以把oldEndVnode.elm移动到oldStartVnode.elm之前，然后把newStartVnode设置为下一个节点，oldEndVnode设置为上一个节点，重复上述流程
如果以上都不匹配，就尝试在oldChildren中寻找跟newStartVnode具有相同key的节点，如果找不到相同key的节点，说明newStartVnode是一个新节点，就创建一个，然后把newStartVnode设置为下一个节点
如果上一步找到了跟newStartVnode相同key的节点，那么通过其他属性的比较来判断这2个节点是否是同一个节点，如果是，就调用patchVnode进行patch，如果removeOnly是false，就把newStartVnode.elm插入到oldStartVnode.elm之前，把newStartVnode设置为下一个节点，重复上述流程
如果在oldChildren中没有寻找到newStartVnode的同一节点，那就创建一个新节点，把newStartVnode设置为下一个节点，重复上述流程
如果oldStartVnode跟oldEndVnode重合了，并且newStartVnode跟newEndVnode也重合了，这个循环就结束了
具体代码如下：
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, 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)
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(oldCh, oldStartIdx, oldEndIdx)
}
}
具体的Diff分析
不设key，newCh和oldCh只会进行头尾两端的相互比较，设key后，除了头尾两端的比较外，还会从用key生成的对象oldKeyToIdx中查找匹配的节点，所以为节点设置key可以更高效的利用dom。
diff的遍历过程中，只要是对dom进行的操作都调用api.insertBefore，api.insertBefore只是原生insertBefore的简单封装。
比较分为两种，一种是有vnode.key的，一种是没有的。但这两种比较对真实dom的操作是一致的。
对于与sameVnode(oldStartVnode, newStartVnode)和sameVnode(oldEndVnode,newEndVnode)为true的情况，不需要对dom进行移动。
总结遍历过程，有3种dom操作：上述图中都有
当oldStartVnode，newEndVnode值得比较，说明oldStartVnode.el跑到oldEndVnode.el的后边了。
当oldEndVnode，newStartVnode值得比较，oldEndVnode.el跑到了oldStartVnode.el的前边，准确的说应该是oldEndVnode.el需要移动到oldStartVnode.el的前边”。
newCh中的节点oldCh里没有， 将新节点插入到oldStartVnode.el的前边
在结束时，分为两种情况：
oldStartIdx > oldEndIdx，可以认为oldCh先遍历完。当然也有可能newCh此时也正好完成了遍历，统一都归为此类。此时newStartIdx和newEndIdx之间的vnode是新增的，调用addVnodes，把他们全部插进before的后边，before很多时候是为null的。addVnodes调用的是insertBefore操作dom节点，我们看看insertBefore的文档：parentElement.insertBefore(newElement, referenceElement)
如果referenceElement为null则newElement将被插入到子节点的末尾。如果newElement已经在DOM树中，newElement首先会从DOM树中移除。所以before为null，newElement将被插入到子节点的末尾。
newStartIdx > newEndIdx，可以认为newCh先遍历完。此时oldStartIdx和oldEndIdx之间的vnode在新的子节点里已经不存在了，调用removeVnodes将它们从dom里删除