So verwenden Sie createApp in vue3

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 !== &#39;v-cloak&#39; && /^(v-|:|@)/.test(attr.name)) {
            compatUtils.warnDeprecation(
              DeprecationTypes.GLOBAL_MOUNT_CONTAINER,
              null
            )
            break
          }
        }
      }
    }
 
    // clear content before mounting
    container.innerHTML = &#39;&#39;
    const proxy = mount(container, false, container instanceof SVGElement)
    if (container instanceof Element) {
      container.removeAttribute(&#39;v-cloak&#39;)
      container.setAttribute(&#39;data-v-app&#39;, &#39;&#39;)
    }
    return proxy
  }
 
  return app
}) as CreateAppFunction<Element>

// 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
  }
 .....
}

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
    )
  }

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
          )
        }
      }
    }