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这篇文章主要介绍“vue3中的createApp怎么使用”，在日常操作中，相信很多人在vue3中的createApp怎么使用问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”vue3中的createApp怎么使用”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
createApp函数定义在文件 packages/runtime-dom/src/index.ts中
export const createApp = ((...args) => {
const app = ensureRenderer().createApp(...args)
if (__DEV__) {
injectNativeTagCheck(app)
injectCompilerOptionsCheck(app)
}
const { mount } = app
app.mount = (containerOrSelector: Element | ShadowRoot | string): any => {
const container = normalizeContainer(containerOrSelector)
if (!container) return
const component = app._component
if (!isFunction(component) && !component.render && !component.template) {
// __UNSAFE__
// Reason: potential execution of JS expressions in in-DOM template.
// The user must make sure the in-DOM template is trusted. If it's
// rendered by the server, the template should not contain any user data.
component.template = container.innerHTML
// 2.x compat check
if (__COMPAT__ && __DEV__) {
for (let i = 0; i < container.attributes.length; i++) {
const attr = container.attributes[i]
if (attr.name !== 'v-cloak' && /^(v-|:|@)/.test(attr.name)) {
compatUtils.warnDeprecation(
DeprecationTypes.GLOBAL_MOUNT_CONTAINER,
null
)
break
}
}
}
}
// clear content before mounting
container.innerHTML = ''
const proxy = mount(container, false, container instanceof SVGElement)
if (container instanceof Element) {
container.removeAttribute('v-cloak')
container.setAttribute('data-v-app', '')
}
return proxy
}
return app
}) as CreateAppFunction<Element>(1)首先创建App对象
(2)取出app对象中的mount方法，重写mount方法
首先调用 normalizeContainer 函数来获取container节点
清空container的innerHTML
调用原mount方法
其函数定义为
function ensureRenderer() {
return (
renderer ||
(renderer = createRenderer<Node, Element | ShadowRoot>(rendererOptions))
)
}ensureRenderer通过调用createRenderer，createRenderer函数定义在 packages/runtime-core/src/renderer.ts文件中
export function createRenderer<
HostNode = RendererNode,
HostElement = RendererElement
>(options: RendererOptions<HostNode, HostElement>) {
return baseCreateRenderer<HostNode, HostElement>(options)
}最终是调用baseCreateRenderer，其最终返回
return {
render,
hydrate,
createApp: createAppAPI(render, hydrate)
}createAppAPI函数定义在 packages/runtime-core/src/apiCreateApp.ts文件中，其返回函数
return function createApp(rootComponent, rootProps = null)
其定义在packages/runtime-core/src/apiCreateApp.ts文件
mount(
rootContainer: HostElement,
isHydrate?: boolean,
isSVG?: boolean
): any {
if (!isMounted) {
const vnode = createVNode(
rootComponent as ConcreteComponent,
rootProps
)
// store app context on the root VNode.
// this will be set on the root instance on initial mount.
vnode.appContext = context
// HMR root reload
if (__DEV__) {
context.reload = () => {
render(cloneVNode(vnode), rootContainer, isSVG)
}
}
if (isHydrate && hydrate) {
hydrate(vnode as VNode<Node, Element>, rootContainer as any)
} else {
render(vnode, rootContainer, isSVG)
}
isMounted = true
app._container = rootContainer
// for devtools and telemetry
;(rootContainer as any).__vue_app__ = app
if (__DEV__ || __FEATURE_PROD_DEVTOOLS__) {
app._instance = vnode.component
devtoolsInitApp(app, version)
}
return vnode.component!.proxy
} else if (__DEV__) {
warn(
`App has already been mounted.\n` +
`If you want to remount the same app, move your app creation logic ` +
`into a factory function and create fresh app instances for each ` +
`mount - e.g. \`const createMyApp = () => createApp(App)\``
)
}
}（1）调用createVNode创建虚拟结点
（2）调用 render 函数来实现渲染vnode。render函数是baseCreateRenderer 函数返回调用 createAppAPI 时传入的参数之一
// implementation
function baseCreateRenderer(
options: RendererOptions,
createHydrationFns?: typeof createHydrationFunctions
): any {
....
const render: RootRenderFunction = (vnode, container, isSVG) => {
if (vnode == null) {
if (container._vnode) {
unmount(container._vnode, null, null, true)
}
} else {
patch(container._vnode || null, vnode, container, null, null, null, isSVG)
}
flushPostFlushCbs()
container._vnode = vnode
}
.....
}函数定义在 packages/runtime-core/src/renderer.ts文件中
const patch: PatchFn = (
n1,
n2,
container,
anchor = null,
parentComponent = null,
parentSuspense = null,
isSVG = false,
slotScopeIds = null,
optimized = __DEV__ && isHmrUpdating ? false : !!n2.dynamicChildren
) => {
// 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(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
break
default:
if (shapeFlag & ShapeFlags.ELEMENT) {
processElement(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
} else if (shapeFlag & ShapeFlags.COMPONENT) {
processComponent(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
} else if (shapeFlag & ShapeFlags.TELEPORT) {
;(type as typeof TeleportImpl).process(
n1 as TeleportVNode,
n2 as TeleportVNode,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized,
internals
)
} else if (__FEATURE_SUSPENSE__ && shapeFlag & ShapeFlags.SUSPENSE) {
;(type as typeof SuspenseImpl).process(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized,
internals
)
} else if (__DEV__) {
warn('Invalid VNode type:', type, `(${typeof type})`)
}
}
// set ref
if (ref != null && parentComponent) {
setRef(ref, n1 && n1.ref, parentSuspense, n2 || n1, !n2)
}
}
const patch: PatchFn = (
n1,
n2,
container,
anchor = null,
parentComponent = null,
parentSuspense = null,
isSVG = false,
slotScopeIds = null,
optimized = __DEV__ && isHmrUpdating ? false : !!n2.dynamicChildren
) => {
// patching & not same type, unmount old tree
if (n1 && !isSameVNodeType(n1, n2)) {
anchor = getNextHostNode(n1)
unmount(n1, parentComponent, parentSuspense, true)
n1 = null
}
if (n2.patchFlag === PatchFlags.BAIL) {
optimized = false
n2.dynamicChildren = null
}
const { type, ref, shapeFlag } = n2
switch (type) {
case Text:
processText(n1, n2, container, anchor)
break
case Comment:
processCommentNode(n1, n2, container, anchor)
break
case Static:
if (n1 == null) {
mountStaticNode(n2, container, anchor, isSVG)
} else if (__DEV__) {
patchStaticNode(n1, n2, container, isSVG)
}
break
case Fragment:
processFragment(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
break
default:
if (shapeFlag & ShapeFlags.ELEMENT) {
processElement(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
} else if (shapeFlag & ShapeFlags.COMPONENT) {
processComponent(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
} else if (shapeFlag & ShapeFlags.TELEPORT) {
;(type as typeof TeleportImpl).process(
n1 as TeleportVNode,
n2 as TeleportVNode,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized,
internals
)
} else if (__FEATURE_SUSPENSE__ && shapeFlag & ShapeFlags.SUSPENSE) {
;(type as typeof SuspenseImpl).process(
n1,
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized,
internals
)
} else if (__DEV__) {
warn('Invalid VNode type:', type, `(${typeof type})`)
}
}
// set ref
if (ref != null && parentComponent) {
setRef(ref, n1 && n1.ref, parentSuspense, n2 || n1, !n2)
}
}函数定义在packages/runtime-core/src/renderer.ts文件中
const processComponent = (
n1: VNode | null,
n2: VNode,
container: RendererElement,
anchor: RendererNode | null,
parentComponent: ComponentInternalInstance | null,
parentSuspense: SuspenseBoundary | null,
isSVG: boolean,
slotScopeIds: string[] | null,
optimized: boolean
) => {
n2.slotScopeIds = slotScopeIds
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)
}
}比较旧的虚拟结点n1和新的虚拟节点n2，如果n1为空则挂载结点，否则更新结点。此时n1为空，执行mountComponent挂载结点
函数定义在packages/runtime-core/src/renderer.ts文件中
const mountComponent: MountComponentFn = (
initialVNode,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
optimized
) => {
// 2.x compat may pre-creaate the component instance before actually
// mounting
const compatMountInstance =
__COMPAT__ && initialVNode.isCompatRoot && initialVNode.component
const instance: ComponentInternalInstance =
compatMountInstance ||
(initialVNode.component = createComponentInstance(
initialVNode,
parentComponent,
parentSuspense
))
// inject renderer internals for keepAlive
if (isKeepAlive(initialVNode)) {
;(instance.ctx as KeepAliveContext).renderer = internals
}
// resolve props and slots for setup context
if (!(__COMPAT__ && compatMountInstance)) {
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
)
}其执行流程为
（1）首先调用createComponentInstance创建组件的实例对象
（2）调用setupComponent来初始化属性及slots属性
（3）调用设置和渲染有副作用的函数setupRenderEffect，主要是执行ReactiveEffect的run方法来执行componentUpdateFn以及调度queueJob。
函数定义在packages/runtime-core/src/renderer.ts文件中，关键的是当中定义的函数componentUpdateFn
const componentUpdateFn = () => {
if (!instance.isMounted) {
let vnodeHook: VNodeHook | null | undefined
const { el, props } = initialVNode
const { bm, m, parent } = instance
effect.allowRecurse = false
// beforeMount hook
if (bm) {
invokeArrayFns(bm)
}
// onVnodeBeforeMount
if ((vnodeHook = props && props.onVnodeBeforeMount)) {
invokeVNodeHook(vnodeHook, parent, initialVNode)
}
if (
__COMPAT__ &&
isCompatEnabled(DeprecationTypes.INSTANCE_EVENT_HOOKS, instance)
) {
instance.emit('hook:beforeMount')
}
effect.allowRecurse = true
if (el && hydrateNode) {
// vnode has adopted host node - perform hydration instead of mount.
const hydrateSubTree = () => {
instance.subTree = renderComponentRoot(instance)
hydrateNode!(
el as Node,
instance.subTree,
instance,
parentSuspense,
null
)
}
if (isAsyncWrapper(initialVNode)) {
(initialVNode.type as ComponentOptions).__asyncLoader!().then(
// note: we are moving the render call into an async callback,
// which means it won't track dependencies - but it's ok because
// a server-rendered async wrapper is already in resolved state
// and it will never need to change.
() => !instance.isUnmounted && hydrateSubTree()
)
} else {
hydrateSubTree()
}
} else {
const subTree = (instance.subTree = renderComponentRoot(instance))
patch(
null,
subTree,
container,
anchor,
instance,
parentSuspense,
isSVG
)
initialVNode.el = subTree.el
}
// mounted hook
if (m) {
queuePostRenderEffect(m, parentSuspense)
}
// onVnodeMounted
if ((vnodeHook = props && props.onVnodeMounted)) {
const scopedInitialVNode = initialVNode
queuePostRenderEffect(
() => invokeVNodeHook(vnodeHook!, parent, scopedInitialVNode),
parentSuspense
)
}
if (
__COMPAT__ &&
isCompatEnabled(DeprecationTypes.INSTANCE_EVENT_HOOKS, instance)
) {
queuePostRenderEffect(
() => instance.emit('hook:mounted'),
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
if (initialVNode.shapeFlag & ShapeFlags.COMPONENT_SHOULD_KEEP_ALIVE) {
instance.a && queuePostRenderEffect(instance.a, parentSuspense)
if (
__COMPAT__ &&
isCompatEnabled(DeprecationTypes.INSTANCE_EVENT_HOOKS, instance)
) {
queuePostRenderEffect(
() => instance.emit('hook:activated'),
parentSuspense
)
}
}
instance.isMounted = true
// #2458: deference mount-only object parameters to prevent memleaks
initialVNode = container = anchor = null as any
} 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 (next) {
next.el = vnode.el
updateComponentPreRender(instance, next, optimized)
} else {
next = vnode
}
// Disallow component effect recursion during pre-lifecycle hooks.
effect.allowRecurse = false
// beforeUpdate hook
if (bu) {
invokeArrayFns(bu)
}
// onVnodeBeforeUpdate
if ((vnodeHook = next.props && next.props.onVnodeBeforeUpdate)) {
invokeVNodeHook(vnodeHook, parent, next, vnode)
}
if (
__COMPAT__ &&
isCompatEnabled(DeprecationTypes.INSTANCE_EVENT_HOOKS, instance)
) {
instance.emit('hook:beforeUpdate')
}
effect.allowRecurse = true
// render
const nextTree = renderComponentRoot(instance)
const prevTree = instance.subTree
instance.subTree = nextTree
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
)
}
if (
__COMPAT__ &&
isCompatEnabled(DeprecationTypes.INSTANCE_EVENT_HOOKS, instance)
) {
queuePostRenderEffect(
() => instance.emit('hook:updated'),
parentSuspense
)
}
}
}如果组件没有挂载，则挂载组件，并在挂载完把组件的 isMounted 属性设置为true，表示已挂载。如果已经挂载，则更新组件。
递归调用 patch 函数挂载组件
函数定义在packages/runtime-core/src/renderer.ts文件中
const processFragment = (
n1: VNode | null,
n2: VNode,
container: RendererElement,
anchor: RendererNode | null,
parentComponent: ComponentInternalInstance | null,
parentSuspense: SuspenseBoundary | null,
isSVG: boolean,
slotScopeIds: string[] | null,
optimized: boolean
) => {
const fragmentStartAnchor = (n2.el = n1 ? n1.el : hostCreateText(''))!
const fragmentEndAnchor = (n2.anchor = n1 ? n1.anchor : hostCreateText(''))!
let { patchFlag, dynamicChildren, slotScopeIds: fragmentSlotScopeIds } = n2
if (dynamicChildren) {
optimized = true
}
// check if this is a slot fragment with :slotted scope ids
if (fragmentSlotScopeIds) {
slotScopeIds = slotScopeIds
? slotScopeIds.concat(fragmentSlotScopeIds)
: fragmentSlotScopeIds
}
if (n1 == null) {
hostInsert(fragmentStartAnchor, container, anchor)
hostInsert(fragmentEndAnchor, container, anchor)
// a fragment can only have array children
// since they are either generated by the compiler, or implicitly created
// from arrays.
mountChildren(
n2.children as VNodeArrayChildren,
container,
fragmentEndAnchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
} else {
if (
patchFlag > 0 &&
patchFlag & PatchFlags.STABLE_FRAGMENT &&
dynamicChildren &&
// #2715 the previous fragment could've been a BAILed one as a result
// of renderSlot() with no valid children
n1.dynamicChildren
) {
// a stable fragment (template root or <template v-for>) doesn't need to
// patch children order, but it may contain dynamicChildren.
patchBlockChildren(
n1.dynamicChildren,
dynamicChildren,
container,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds
)
if (__DEV__ && parentComponent && parentComponent.type.__hmrId) {
traverseStaticChildren(n1, n2)
} else if (
// #2080 if the stable fragment has a key, it's a <template v-for> that may
// get moved around. Make sure all root level vnodes inherit el.
// #2134 or if it's a component root, it may also get moved around
// as the component is being moved.
n2.key != null ||
(parentComponent && n2 === parentComponent.subTree)
) {
traverseStaticChildren(n1, n2, true /* shallow */)
}
} else {
// keyed / unkeyed, or manual fragments.
// for keyed & unkeyed, since they are compiler generated from v-for,
// each child is guaranteed to be a block so the fragment will never
// have dynamicChildren.
patchChildren(
n1,
n2,
container,
fragmentEndAnchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
}
}
}（1）如果n1为空，则执行mountChildren
（2）否则执行patchChildren
函数定义在packages/runtime-core/src/renderer.ts文件中
const mountChildren: MountChildrenFn = (
children,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized,
start = 0
) => {
for (let i = start; i < children.length; i++) {
const child = (children[i] = optimized
? cloneIfMounted(children[i] as VNode)
: normalizeVNode(children[i]))
patch(
null,
child,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
}
}遍历children,执行patch挂载所有子元素
函数定义在packages/runtime-core/src/renderer.ts文件中
const processElement = (
n1: VNode | null,
n2: VNode,
container: RendererElement,
anchor: RendererNode | null,
parentComponent: ComponentInternalInstance | null,
parentSuspense: SuspenseBoundary | null,
isSVG: boolean,
slotScopeIds: string[] | null,
optimized: boolean
) => {
isSVG = isSVG || (n2.type as string) === 'svg'
if (n1 == null) {
mountElement(
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
} else {
patchElement(
n1,
n2,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
}
}（1）如果n1为空，则调用mountElement挂载元素
（2）如果n1不为空，则调用patchElement来更新元素
此时，执行挂载元素。
函数定义在packages/runtime-core/src/renderer.ts文件中
const processElement = (
n1: VNode | null,
n2: VNode,
container: RendererElement,
anchor: RendererNode | null,
parentComponent: ComponentInternalInstance | null,
parentSuspense: SuspenseBoundary | null,
isSVG: boolean,
slotScopeIds: string[] | null,
optimized: boolean
) => {
isSVG = isSVG || (n2.type as string) === 'svg'
if (n1 == null) {
mountElement(
n2,
container,
anchor,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
} else {
patchElement(
n1,
n2,
parentComponent,
parentSuspense,
isSVG,
slotScopeIds,
optimized
)
}
}（1）调用hostCreateElement根据类型和其他属性，创建DOM元素节点
（2）判断子节点的类型，若子节点为纯文本，则直接处理纯文本hostSetElementText，若子节点为数组，则调用 mountChildren 函数深度遍历处理子节点
（3）处理 props 属性,主要是调用hostPatchProp和setScopeId
（4）调用hostInsert将el挂载到 container 中
到此，关于“vue3中的createApp怎么使用”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注亿速云网站，小编会继续努力为大家带来更多实用的文章！
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