# 渲染器
渲染器的作用是将虚拟DOM渲染为真实DOM。
# VNode
# VNode的类型
常规的VNode包括Text、Comment、Static、Fragment这几种类型。
// 所有VNode类型
export type VNodeTypes =
| string
| VNode
| Component
| typeof Text
| typeof Static
| typeof Comment
| typeof Fragment
| typeof TeleportImpl
| typeof SuspenseImpl
export const Text = Symbol(__DEV__ ? 'Text' : undefined) // 纯文本
export const Comment = Symbol(__DEV__ ? 'Comment' : undefined) // 注释类
export const Static = Symbol(__DEV__ ? 'Static' : undefined) // 静态html
export const Fragment = (Symbol(__DEV__ ? 'Fragment' : undefined) as any) as {
__isFragment: true
new (): {
$props: VNodeProps
}
} // fragment html片段，根节点是多个节点
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VNode的内容：
const vnode: VNode = {
__v_isVNode: true,
[ReactiveFlags.SKIP]: true,
type,
props,
key: props && normalizeKey(props),
ref: props && normalizeRef(props),
scopeId: currentScopeId,
children: null,
component: null,
suspense: null,
ssContent: null,
ssFallback: null,
dirs: null,
transition: null,
el: null,
anchor: null,
target: null,
targetAnchor: null,
staticCount: 0,
shapeFlag, // 用于
patchFlag,
dynamicProps,
dynamicChildren: null,
appContext: null
}
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createVNode位于@vue/runtime-core/vnode.ts，在生产环境调用了第317行的_createVNode，其代码如下：
function _createVNode(
type: VNodeTypes | ClassComponent | typeof NULL_DYNAMIC_COMPONENT,
props: (Data & VNodeProps) | null = null,
children: unknown = null,
patchFlag: number = 0,
dynamicProps: string[] | null = null,
isBlockNode = false
): VNode {
if (!type || type === NULL_DYNAMIC_COMPONENT) {
type = Comment
}
if (isVNode(type)) {
// createVNode receiving an existing vnode. This happens in cases like
// <component :is="vnode"/>
// #2078 make sure to merge refs during the clone instead of overwriting it
const cloned = cloneVNode(type, props, true /* mergeRef: true */)
if (children) {
normalizeChildren(cloned, children)
}
return cloned
}
// class component normalization.
if (isClassComponent(type)) {
type = type.__vccOpts
}
// class & style normalization.
if (props) {
// for reactive or proxy objects, we need to clone it to enable mutation.
if (isProxy(props) || InternalObjectKey in props) {
props = extend({}, props)
}
let { class: klass, style } = props
if (klass && !isString(klass)) {
props.class = normalizeClass(klass)
}
if (isObject(style)) {
// reactive state objects need to be cloned since they are likely to be
// mutated
if (isProxy(style) && !isArray(style)) {
style = extend({}, style)
}
props.style = normalizeStyle(style)
}
}
// encode the vnode type information into a bitmap
const shapeFlag = isString(type)
? ShapeFlags.ELEMENT
: __FEATURE_SUSPENSE__ && isSuspense(type)
? ShapeFlags.SUSPENSE
: isTeleport(type)
? ShapeFlags.TELEPORT
: isObject(type)
? ShapeFlags.STATEFUL_COMPONENT
: isFunction(type)
? ShapeFlags.FUNCTIONAL_COMPONENT
: 0
const vnode: VNode = {
// ... 省略VNode内容
}
normalizeChildren(vnode, children)
// normalize suspense children
if (__FEATURE_SUSPENSE__ && shapeFlag & ShapeFlags.SUSPENSE) {
const { content, fallback } = normalizeSuspenseChildren(vnode)
vnode.ssContent = content
vnode.ssFallback = fallback
}
if (
shouldTrack > 0 &&
// avoid a block node from tracking itself
!isBlockNode &&
// has current parent block
currentBlock &&
// presence of a patch flag indicates this node needs patching on updates.
// component nodes also should always be patched, because even if the
// component doesn't need to update, it needs to persist the instance on to
// the next vnode so that it can be properly unmounted later.
(patchFlag > 0 || shapeFlag & ShapeFlags.COMPONENT) &&
// the EVENTS flag is only for hydration and if it is the only flag, the
// vnode should not be considered dynamic due to handler caching.
patchFlag !== PatchFlags.HYDRATE_EVENTS
) {
currentBlock.push(vnode)
}
return vnode
}
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# 渲染器的基本结构
在Vue3中渲染器被抽象成了一个对象，其TypeScript类型定义位于@vue/runtime-core/renderer.ts中：
export interface Renderer<HostElement = RendererElement> {
render: RootRenderFunction<HostElement>
createApp: CreateAppFunction<HostElement>
}
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主要就是一个拥有render和createApp方法的对象。
在Vue3中可以通过createRenderer自定义渲染器，浏览器平台的DOM渲染器就是自定义渲染器的一个实现。
export function createRenderer<
HostNode = RendererNode,
HostElement = RendererElement
>(options: RendererOptions<HostNode, HostElement>) {
return baseCreateRenderer<HostNode, HostElement>(options)
}
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createRenderer函数将自定义渲染器的依赖抽象成了RendererOptions，其TypeScript类型定义如下：
export interface RendererOptions<
HostNode = RendererNode,
HostElement = RendererElement
> {
patchProp(
el: HostElement,
key: string,
prevValue: any,
nextValue: any,
isSVG?: boolean,
prevChildren?: VNode<HostNode, HostElement>[],
parentComponent?: ComponentInternalInstance | null,
parentSuspense?: SuspenseBoundary | null,
unmountChildren?: UnmountChildrenFn
): void
insert(el: HostNode, parent: HostElement, anchor?: HostNode | null): void
remove(el: HostNode): void
createElement(
type: string,
isSVG?: boolean,
isCustomizedBuiltIn?: string,
vnodeProps?: (VNodeProps & { [key: string]: any }) | null
): HostElement
createText(text: string): HostNode
createComment(text: string): HostNode
setText(node: HostNode, text: string): void
setElementText(node: HostElement, text: string): void
parentNode(node: HostNode): HostElement | null
nextSibling(node: HostNode): HostNode | null
querySelector?(selector: string): HostElement | null
setScopeId?(el: HostElement, id: string): void
cloneNode?(node: HostNode): HostNode
insertStaticContent?(
content: string,
parent: HostElement,
anchor: HostNode | null,
isSVG: boolean,
start?: HostNode | null,
end?: HostNode | null
): [HostNode, HostNode]
}
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# mount
app的mount方法中的render由createAppAPI作为参数传入，来源于@vue/runtime-core/renderer.ts中的baseCreateRenderer方法定义：
const render: RootRenderFunction = (vnode, container) => {
if (vnode == null) {
if (container._vnode) {
unmount(container._vnode, null, null, true)
}
} else {
patch(container._vnode || null, vnode, container)
}
flushPostFlushCbs() // TODO 待解析
container._vnode = vnode
}
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render方法主要有两个逻辑分支，如果vnode不为null时，为新建或者更新逻辑，调用patch方法；如果vnode为null，，并且container._vnode不为null，即vnode从有值变为null，调用unmount方法。
# patch
patch函数是整个渲染器的核心入口，承载了最重要的渲染逻辑
# patch的类型
不同类型的元素或组件，有不同的patch策略
export const enum PatchFlags {
// 表明元素具有动态文本
TEXT = 1,
// 表明元素具有动态class绑定
CLASS = 1 << 1, // 2
// 表明元素具有动态样式style，编译器会将静态对象字符串编译为静态对象，并做变量提升优化
// 例如：
// style="color: red" 或 :style="{ color: 'red' }"
// 将被编译为：
// const style = { color: 'red' }
// render() { return e('div', { style }) }
STYLE = 1 << 2, // 4
// 表明元素或者组件具有class/style以外的动态属性props
// Can also be on a component that has any dynamic props (includes
// class/style). when this flag is present, the vnode also has a dynamicProps
// array that contains the keys of the props that may change so the runtime
// can diff them faster (without having to worry about removed props)
PROPS = 1 << 3, // 8
// Indicates an element with props with dynamic keys. When keys change, a full
// diff is always needed to remove the old key. This flag is mutually
// exclusive with CLASS, STYLE and PROPS.
FULL_PROPS = 1 << 4,
// Indicates an element with event listeners (which need to be attached
// during hydration)
HYDRATE_EVENTS = 1 << 5,
// Indicates a fragment whose children order doesn't change.
STABLE_FRAGMENT = 1 << 6,
// Indicates a fragment with keyed or partially keyed children
KEYED_FRAGMENT = 1 << 7,
// Indicates a fragment with unkeyed children.
UNKEYED_FRAGMENT = 1 << 8,
// Indicates an element that only needs non-props patching, e.g. ref or
// directives (onVnodeXXX hooks). since every patched vnode checks for refs
// and onVnodeXXX hooks, it simply marks the vnode so that a parent block
// will track it.
NEED_PATCH = 1 << 9,
// Indicates a component with dynamic slots (e.g. slot that references a v-for
// iterated value, or dynamic slot names).
// Components with this flag are always force updated.
DYNAMIC_SLOTS = 1 << 10,
// SPECIAL FLAGS -------------------------------------------------------------
// Special flags are negative integers. They are never matched against using
// bitwise operators (bitwise matching should only happen in branches where
// patchFlag > 0), and are mutually exclusive. When checking for a special
// flag, simply check patchFlag === FLAG.
// Indicates a hoisted static vnode. This is a hint for hydration to skip
// the entire sub tree since static content never needs to be updated.
HOISTED = -1,
// A special flag that indicates that the diffing algorithm should bail out
// of optimized mode. For example, on block fragments created by renderSlot()
// when encountering non-compiler generated slots (i.e. manually written
// render functions, which should always be fully diffed)
// OR manually cloneVNodes
BAIL = -2
}
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patch方法位于同文件的452行：
const patch: PatchFn = (
n1, // prev vnode
n2, // current vnode
container,
anchor = null,
parentComponent = null,
parentSuspense = null,
isSVG = false,
optimized = false
) => {
// patching & not same type, unmount old tree
if (n1 && !isSameVNodeType(n1, n2)) {
anchor = getNextHostNode(n1)
unmount(n1, parentComponent, parentSuspense, true)
n1 = null
}
if (n2.patchFlag === PatchFlags.BAIL) {
optimized = false
n2.dynamicChildren = null
}
const { type, ref, shapeFlag } = n2
switch (type) {
case Text:
processText(n1, n2, container, anchor) // 纯文本
break
case Comment:
processCommentNode(n1, n2, container, anchor)
break
case Static:
if (n1 == null) {
mountStaticNode(n2, container, anchor, isSVG)
} else if (__DEV__) {
patchStaticNode(n1, n2, container, isSVG)
}
break
case Fragment:
processFragment(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
optimized
)
break
default:
if (shapeFlag & ShapeFlags.ELEMENT) { // VNode 是普通标签
processElement(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
optimized
)
} else if (shapeFlag & ShapeFlags.COMPONENT) { // VNode 是组件
processComponent(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
optimized
)
} else if (shapeFlag & ShapeFlags.TELEPORT) {
;(type as typeof TeleportImpl).process(
n1 as TeleportVNode,
n2 as TeleportVNode,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
optimized,
internals
)
} else if (__FEATURE_SUSPENSE__ && shapeFlag & ShapeFlags.SUSPENSE) {
;(type as typeof SuspenseImpl).process(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
optimized,
internals
)
}
}
// set ref
if (ref != null && parentComponent) {
setRef(ref, n1 && n1.ref, parentComponent, parentSuspense, n2)
}
}
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patch方法经过swtich语句调用了processComponent方法，其代码位于同文件的第1201行：
const processComponent = (
n1: VNode | null,
n2: VNode,
container: RendererElement,
anchor: RendererNode | null,
parentComponent: ComponentInternalInstance | null,
parentSuspense: SuspenseBoundary | null,
isSVG: boolean,
optimized: boolean
) => {
if (n1 == null) {
if (n2.shapeFlag & ShapeFlags.COMPONENT_KEPT_ALIVE) {
(parentComponent!.ctx as KeepAliveContext).activate(
n2,
container,
anchor,
isSVG,
optimized
)
} else {
mountComponent(
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
optimized
)
}
} else {
updateComponent(n1, n2, optimized)
}
}
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其主要有两个逻辑分支：旧的VNode``n1不为null时，调用更新组件的updateComponent方法；当n1为null时，又有两个子分支：新的VNode``n1为keep-alive的组件时，调用其ctx的activate方法，否则调用挂载组件的mountComponent方法。
我们先看挂载组件的mountComponent方法，其位于processComponent的下方：
const mountComponent: MountComponentFn = (
initialVNode, // 初始的VNode
container, // 挂载的容器
anchor,
parentComponent,
parentSuspense,
isSVG,
optimized
) => {
const instance: ComponentInternalInstance = (initialVNode.component = createComponentInstance(
initialVNode,
parentComponent,
parentSuspense
))
// inject renderer internals for keepAlive
if (isKeepAlive(initialVNode)) {
(instance.ctx as KeepAliveContext).renderer = internals
}
setupComponent(instance)
// setup() is async. This component relies on async logic to be resolved
// before proceeding
if (__FEATURE_SUSPENSE__ && instance.asyncDep) {
parentSuspense && parentSuspense.registerDep(instance, setupRenderEffect)
// Give it a placeholder if this is not hydration
// TODO handle self-defined fallback
if (!initialVNode.el) {
const placeholder = (instance.subTree = createVNode(Comment))
processCommentNode(null, placeholder, container!, anchor)
}
return
}
setupRenderEffect(
instance,
initialVNode,
container,
anchor,
parentSuspense,
isSVG,
optimized
)
}
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# create
首先调用createComponentInstance方法生成组件的实例，先看下组件实例的构成：
const instance: ComponentInternalInstance = {
uid: uid++,
vnode,
type,
parent,
appContext,
root: null!, // to be immediately set
next: null,
subTree: null!, // will be set synchronously right after creation
update: null!, // will be set synchronously right after creation
render: null,
proxy: null,
exposed: null,
withProxy: null,
effects: null,
provides: parent ? parent.provides : Object.create(appContext.provides),
accessCache: null!,
renderCache: [],
// local resovled assets
components: null,
directives: null,
// resolved props and emits options
propsOptions: normalizePropsOptions(type, appContext),
emitsOptions: normalizeEmitsOptions(type, appContext),
// emit
emit: null as any, // to be set immediately
emitted: null,
// state
ctx: EMPTY_OBJ,
data: EMPTY_OBJ,
props: EMPTY_OBJ,
attrs: EMPTY_OBJ,
slots: EMPTY_OBJ,
refs: EMPTY_OBJ,
setupState: EMPTY_OBJ,
setupContext: null,
// suspense related
suspense,
suspenseId: suspense ? suspense.pendingId : 0,
asyncDep: null,
asyncResolved: false,
// lifecycle hooks
// not using enums here because it results in computed properties
isMounted: false,
isUnmounted: false,
isDeactivated: false,
bc: null,
c: null,
bm: null,
m: null,
bu: null,
u: null,
um: null,
bum: null,
da: null,
a: null,
rtg: null,
rtc: null,
ec: null
}
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createComponentInstance方法的代码位于@vue/runtime-core/component.ts的第401行：
export function createComponentInstance(
vnode: VNode,
parent: ComponentInternalInstance | null,
suspense: SuspenseBoundary | null
) {
const type = vnode.type as ConcreteComponent
// inherit parent app context - or - if root, adopt from root vnode
const appContext =
(parent ? parent.appContext : vnode.appContext) || emptyAppContext
const instance: ComponentInternalInstance = {
// 省略componentInstance内容
}
if (__DEV__) { // TODO
instance.ctx = createRenderContext(instance)
} else {
instance.ctx = { _: instance }
}
instance.root = parent ? parent.root : instance
instance.emit = emit.bind(null, instance)
return instance
}
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# setup
setup主要包括setupComponent和setupRenderEffect两个过程。
setupComponent方法代码位于@vue/runtime-core/component.ts的第516行：
export let isInSSRComponentSetup = false // 表明组件是否服务端渲染的变量
export function setupComponent(
instance: ComponentInternalInstance,
isSSR = false
) {
isInSSRComponentSetup = isSSR
const { props, children, shapeFlag } = instance.vnode
const isStateful = shapeFlag & ShapeFlags.STATEFUL_COMPONENT
initProps(instance, props, isStateful, isSSR)
initSlots(instance, children)
const setupResult = isStateful
? setupStatefulComponent(instance, isSSR)
: undefined
isInSSRComponentSetup = false
return setupResult
}
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内部主要做了初始化属性initProps和初始化插槽initSlots这两件事儿，并且带状态isStateful的组件，会执行setupStatefulComponent方法获取setupResult。最后将标识组件是否在SSR环境下执行setup的标识置为false，并返回setupResult。
initProps方法位于@vue/runtime-core/componentProps.ts的第114行：
export function initProps(
instance: ComponentInternalInstance,
rawProps: Data | null,
isStateful: number, // result of bitwise flag comparison
isSSR = false
) {
const props: Data = {}
const attrs: Data = {}
def(attrs, InternalObjectKey, 1)
setFullProps(instance, rawProps, props, attrs)
// validation
if (__DEV__) {
validateProps(props, instance)
}
if (isStateful) {
// stateful
instance.props = isSSR ? props : shallowReactive(props)
} else {
if (!instance.type.props) {
// functional w/ optional props, props === attrs
instance.props = attrs
} else {
// functional w/ declared props
instance.props = props
}
}
instance.attrs = attrs
}
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setFullProps位于同文件：
function setFullProps(
instance: ComponentInternalInstance,
rawProps: Data | null,
props: Data,
attrs: Data
) {
const [options, needCastKeys] = instance.propsOptions
if (rawProps) {
for (const key in rawProps) {
const value = rawProps[key]
// key, ref are reserved and never passed down
if (isReservedProp(key)) {
continue
}
// prop option names are camelized during normalization, so to support
// kebab -> camel conversion here we need to camelize the key.
let camelKey
if (options && hasOwn(options, (camelKey = camelize(key)))) {
props[camelKey] = value
} else if (!isEmitListener(instance.emitsOptions, key)) {
// Any non-declared (either as a prop or an emitted event) props are put
// into a separate `attrs` object for spreading. Make sure to preserve
// original key casing
attrs[key] = value
}
}
}
if (needCastKeys) {
const rawCurrentProps = toRaw(props)
for (let i = 0; i < needCastKeys.length; i++) {
const key = needCastKeys[i]
props[key] = resolvePropValue(
options!,
rawCurrentProps,
key,
rawCurrentProps[key],
instance
)
}
}
}
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shallowReactive为Vue3暴露的响应式核心API之一，用于创建一个不会深度嵌套的响应式proxy。调用了Reactivity部分的核心代码createReactiveObject，通过new Proxy的方式来响应data的变化。
# update
setupRenderEffect主要设置了实例的update方法，此处调用了reactivity中的effect方法，在定义之后会立即执行，出发DOM渲染：
const setupRenderEffect: SetupRenderEffectFn = (
instance,
initialVNode,
container,
anchor,
parentSuspense,
isSVG,
optimized
) => {
// create reactive effect for rendering
instance.update = effect(function componentEffect() {
if (!instance.isMounted) {
let vnodeHook: VNodeHook | null | undefined
const { el, props } = initialVNode
const { bm, m, parent } = instance
// beforeMount hook
if (bm) {
invokeArrayFns(bm)
}
// onVnodeBeforeMount
if ((vnodeHook = props && props.onVnodeBeforeMount)) {
invokeVNodeHook(vnodeHook, parent, initialVNode)
}
const subTree = (instance.subTree = renderComponentRoot(instance))
if (__DEV__) {
endMeasure(instance, `render`)
}
if (el && hydrateNode) {
if (__DEV__) {
startMeasure(instance, `hydrate`)
}
// vnode has adopted host node - perform hydration instead of mount.
hydrateNode(
initialVNode.el as Node,
subTree,
instance,
parentSuspense
)
if (__DEV__) {
endMeasure(instance, `hydrate`)
}
} else {
if (__DEV__) {
startMeasure(instance, `patch`)
}
patch(
null,
subTree,
container,
anchor,
instance,
parentSuspense,
isSVG
)
if (__DEV__) {
endMeasure(instance, `patch`)
}
initialVNode.el = subTree.el
}
// mounted hook
if (m) {
queuePostRenderEffect(m, parentSuspense)
}
// onVnodeMounted
if ((vnodeHook = props && props.onVnodeMounted)) {
queuePostRenderEffect(() => {
invokeVNodeHook(vnodeHook!, parent, initialVNode)
}, parentSuspense)
}
// activated hook for keep-alive roots.
// #1742 activated hook must be accessed after first render
// since the hook may be injected by a child keep-alive
const { a } = instance
if (
a &&
initialVNode.shapeFlag & ShapeFlags.COMPONENT_SHOULD_KEEP_ALIVE
) {
queuePostRenderEffect(a, parentSuspense)
}
instance.isMounted = true
} else {
// updateComponent
// This is triggered by mutation of component's own state (next: null)
// OR parent calling processComponent (next: VNode)
let { next, bu, u, parent, vnode } = instance
let originNext = next
let vnodeHook: VNodeHook | null | undefined
if (__DEV__) {
pushWarningContext(next || instance.vnode)
}
if (next) {
updateComponentPreRender(instance, next, optimized)
} else {
next = vnode
}
next.el = vnode.el
// beforeUpdate hook
if (bu) {
invokeArrayFns(bu)
}
// onVnodeBeforeUpdate
if ((vnodeHook = next.props && next.props.onVnodeBeforeUpdate)) {
invokeVNodeHook(vnodeHook, parent, next, vnode)
}
const nextTree = renderComponentRoot(instance)
if (__DEV__) {
endMeasure(instance, `render`)
}
const prevTree = instance.subTree
instance.subTree = nextTree
// reset refs
// only needed if previous patch had refs
if (instance.refs !== EMPTY_OBJ) {
instance.refs = {}
}
if (__DEV__) {
startMeasure(instance, `patch`)
}
patch(
prevTree,
nextTree,
// parent may have changed if it's in a teleport
hostParentNode(prevTree.el!)!,
// anchor may have changed if it's in a fragment
getNextHostNode(prevTree),
instance,
parentSuspense,
isSVG
)
next.el = nextTree.el
if (originNext === null) {
// self-triggered update. In case of HOC, update parent component
// vnode el. HOC is indicated by parent instance's subTree pointing
// to child component's vnode
updateHOCHostEl(instance, nextTree.el)
}
// updated hook
if (u) {
queuePostRenderEffect(u, parentSuspense)
}
// onVnodeUpdated
if ((vnodeHook = next.props && next.props.onVnodeUpdated)) {
queuePostRenderEffect(() => {
invokeVNodeHook(vnodeHook!, parent, next!, vnode)
}, parentSuspense)
}
}
}, prodEffectOptions)
}
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