从一个单元测试出发，梳理vue3的渲染过程
先来看一个单测。test('receive component instance as 2nd arg', () => {
transformVNodeArgs((args, instance) => {
if (instance) {
return ['h1', null, instance.type.name]
} else {
return args
}
})
const App = {
// this will be the name of the component in the h1
name: 'Root Component',
render() {
return h('p') // this will be overwritten by the transform
}
}
const root = nodeOps.createElement('div')
createApp(App).mount(root)
})我们先从最熟悉的createApp(App).mount(root)这句入手，分两步看起。第一步 createApp(App)创建App实例，第二步mount(root)挂载。
1. createApp
packages\runtime-dom\src\index.ts
const createApp = ((...args) => {
const app = ensureRenderer().createApp(...args);
{
injectNativeTagCheck(app);
}
const { mount } = app;
app.mount = (containerOrSelector) => {
// 调用解构生成的mount方法...
};
return app;
});该方法返回app实例，并在其上定义mount方法，即第二步的mount方法。
此app实例是由ensureRenderer返回render方法调用后的实例，并调用其上的createApp方法生成的。
function ensureRenderer() {
return renderer || (renderer = createRenderer(rendererOptions))
}即 ensureRenderer --> createRenderer --> baseCreateRenderer -->
其中，rendererOptions = extend({ patchProp, forcePatchProp }, nodeOps) ，作为操作DOM的方法。baseCreateRenderer定义了一系列操作的闭包方法，供渲染使用（packages\runtime-core\src\renderer.ts）。
接下来就是createAppAPI(render, hydrate)（packages\runtime-core\src\apiCreateApp.ts）
export function createAppAPI<HostElement>(render: RootRenderFunction,hydrate?: RootHydrateFunction): CreateAppFunction<HostElement> {
return function createApp(rootComponent, rootProps = null) {
//...
//app实例上下文context对象
//config: { isNativeTag: NO, devtools: true, performance: false, globalProperties: {}, optionMergeStrategies: {}, isCustomElement: NO, warnHandler: undefined },
// mixins: [], components: {}, directives: {}, provides: Object.create(null) }
const context = createAppContext()
const installedPlugins = new Set()
let isMounted = false
const app: App = { nder: RootRenderFunction,hydrate?: RootHydrateFunction): CreateAppFunction<HostElement> {
_component: rootComponent as Component,
_props: rootProps,
_container: null,
_context: context,
version,
get config() {
return context.config
},
set config(v) {
if (__DEV__) {
warn( `app.config cannot be replaced. Modify individual options instead.`)
}
},
use(plugin: Plugin, ...options: any[]) {},
mixin(mixin: ComponentOptions) {},
component(name: string, component?: PublicAPIComponent): any {},
directive(name: string, directive?: Directive) {},
mount(rootContainer: HostElement, isHydrate?: boolean): any {}
unmount() {}
provide(key, value) {}
}
return app
}
}mount方法就是在第二步中的主要逻辑。
function injectNativeTagCheck(app: App) {
// Inject `isNativeTag`
// this is used for component name validation (dev only)
Object.defineProperty(app.config, 'isNativeTag', {
value: (tag: string) => isHTMLTag(tag) || isSVGTag(tag),
writable: false
})
}注入验证组件name的isNativeTag。至此，第一步告一段落。
2. mount
挂载：
const { mount } = app
app.mount = (containerOrSelector: Element | string): any => {
const container = normalizeContainer(containerOrSelector)// document.querySelector(container)或者container
if (!container) return const component = app._component // App根组件
if (!isFunction(component) && !component.render && !component.template) {
component.template = container.innerHTML
}
// clear content before mounting
container.innerHTML = ''
const proxy = mount(container)
container.removeAttribute('v-cloak')
return proxy
}mount的过程：
function mount(rootContainer: HostElement, isHydrate?: boolean): any {
if (!isMounted) {
const vnode = createVNode(rootComponent as Component, rootProps)
// store app context on the root VNode.
// this will be set on the root instance on initial mount.
vnode.appContext = context // createApp时创建的app上下文
// HMR root reload
if (__DEV__) {
context.reload = () => { // 什么时候触发？？？
render(cloneVNode(vnode), rootContainer)
}
}
if (isHydrate && hydrate) {
hydrate(vnode as VNode<Node, Element>, rootContainer as any)
} else {
render(vnode, rootContainer)
}
isMounted = true
app._container = rootContainer
return vnode.component!.proxy
}
}isMounted为false，基于根组件创建vnode，绑定上下文，执行render函数完成页面渲染，isMounted置为true，app实例的_container绑定根DOM元素root。
接下来就是老太太裹脚布般的render过程：
const render: RootRenderFunction = (vnode, container) => {
if (vnode == null) {
if (container._vnode) {
unmount(container._vnode, null, null, true) // 卸载
}
} else {
patch(container._vnode || null, vnode, container)
}
flushPostFlushCbs() // check递归次数
container._vnode = vnode
}patch(null, vnode, container)打补丁。
const patch: PatchFn = (
n1,
n2,
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)
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(/*参数还是那些参数*/)
break
default:
if (shapeFlag & ShapeFlags.ELEMENT) {
processElement(/*参数还是那些参数*/)
} else if (shapeFlag & ShapeFlags.COMPONENT) {
processComponent(/*参数还是那些参数*/)
} else if (shapeFlag & ShapeFlags.TELEPORT) {
;(type as typeof TeleportImpl).process( /*参数还是那些参数,*/ internals )
} else if (__FEATURE_SUSPENSE__ && shapeFlag & ShapeFlags.SUSPENSE) {
;(type as typeof SuspenseImpl).process( /*参数还是那些参数,*/ internals )
} else if (__DEV__) {
warn('Invalid VNode type:', type, `(${typeof type})`)
}
}
// set ref
if (ref != null && parentComponent) {
setRef(ref, n1 && n1.ref, parentComponent, parentSuspense, n2)
}
}在这个单元测试的情况下，type是App对象，即Object类型。ref为undefined，shapeFlag为4，所以来到了processComponent方法。
processComponent
--> mountComponent
--> instance = createComponentInstance(vnode, parent = null, suspense = null)
--> instance.ctx = createRenderContext(instance)
--> setupComponent(instance)
--> initProps(instance, props = null, isStateful = 4, isSSR = false)
--> initSlots(instance, children = null)
--> setupStatefulComponent(instance, isSSR)
-->setupRenderEffect( instance, initialVNode, container, anchor, parentSuspense, isSVG, optimized )
normalizePropsOptions函数可以看做类似扁平化，返回的是,是对props、extends、mixins中的props做递归，浅拷贝得到的props和驼峰命名的key的集合。
initProps初始化给instance实例的props和attrs，并对props最外层数据做响应式。
initSlot初始化给instance实例的slots为响应的vnode
setupStatefulComponent先对组件名、子组件名以及指令进行预判，给instance添加给accessCache、proxy属性，执行setup方法，然后给instance添加render函数（与vue2相同，去组件的render函数或者编译template生成），最后是一些兼容2.x的操作。
最后是setupRenderEffect方法，根据instance.isMounted属性判断是首次渲染还是更新，执行patch --> processElement --> mountElement，呈现视图。
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