How to use createApp in vue3

Function definition

The createApp function is defined in the file packages/runtime-dom/src/index.ts

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>

(1) First create the App object

(2 ) Take out the mount method in the app object and rewrite the mount method

• First call the normalizeContainer function to get the container node

• Clear the innerHTML of the container

• Call the original mount method

ensureRenderer

The function is defined as

function ensureRenderer() {
  return (
    renderer ||
    (renderer = createRenderer<Node, Element | ShadowRoot>(rendererOptions))
  )
}

ensureRenderer calls createRenderer, and the createRenderer function is defined in the packages/runtime-core/src/renderer.ts file

export function createRenderer<
  HostNode = RendererNode,
  HostElement = RendererElement
>(options: RendererOptions<HostNode, HostElement>) {
  return baseCreateRenderer<HostNode, HostElement>(options)
}

Ultimately, baseCreateRenderer is called, which ultimately returns

return {
    render,
    hydrate,
    createApp: createAppAPI(render, hydrate)
  }

createAppAPI

The createAppAPI function is defined in the packages/runtime-core/src/apiCreateApp.ts file, and its return function

return function createApp(rootComponent, rootProps = null)

mount

is defined in packages/runtime- core/src/apiCreateApp.ts file

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) Call createVNode to create a virtual node

(2) Call the render function to implement rendering vnode. The render function is one of the parameters passed in when calling createAppAPI returned by the baseCreateRenderer function

// 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
  }
 .....
}

patch

The function is defined in the packages/runtime-core/src/renderer.ts file

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)
    }
  }

processComponent

The function is defined in the packages/runtime-core/src/renderer.ts file

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)
    }
  }

Compare the old and new virtual nodes n1 and n2. If n1 is empty, mount the node ; Otherwise, update the node. At this time n1 is empty, execute mountComponent to mount the node

mountComponent

The function is defined in the packages/runtime-core/src/renderer.ts file

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
    )
  }

its execution The process is

(1) First call createComponentInstance to create an instance object of the component

(2) Call setupComponent to initialize properties and slots properties

(3) Call setup and rendering The side effect function setupRenderEffect mainly executes the run method of ReactiveEffect to execute componentUpdateFn and schedule queueJob.

setupRenderEffect

The function is defined in the packages/runtime-core/src/renderer.ts file. The key is the function 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
          )
        }
      }
    }

When the component has not been When mounting, you need to mount it, and after the mounting is completed, set the component's isMounted attribute to true to indicate that the component has been successfully mounted. If already mounted, update the component.

Recursively call the patch function to mount the component

processFragment

The function is defined in the packages/runtime-core/src/renderer.ts file

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&#39;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&#39;s a <template v-for> that may
          //  get moved around. Make sure all root level vnodes inherit el.
          // #2134 or if it&#39;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) If n1 is empty, execute mountChildren

(2) Otherwise execute patchChildren

mountChildren

function defined in packages/runtime-core/src/renderer.ts file Middle

  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
      )
    }
  }

Traverse children and execute patch to mount all child elements

processElement

The function is defined in the packages/runtime-core/src/renderer.ts file

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) If n1 is empty, call mountElement to mount the element

(2) If n1 is not empty, call patchElement to update the element

At this time, execute the mount load element.

mountElement

The function is defined in the packages/runtime-core/src/renderer.ts file

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) Call hostCreateElement to create a DOM element based on the type and other attributes Node

(2) Determine the type of the child node. If the child node is plain text, the plain text hostSetElementText is processed directly. If the child node is an array, the mountChildren function is called to deeply traverse the child node

( 3) Process props attributes, mainly calling hostPatchProp and setScopeId

(4) Call hostInsert to mount el into the container

The above is the detailed content of How to use createApp in vue3. For more information, please follow other related articles on the PHP Chinese website!