Vue.createApp(App).mount('#app')执行过程

1.创建app入口

2.render函数

3.返回app

mount

App组件的挂载和渲染过程

1. patch:进行diff算法.

2. 处理组件节点.

3. 调用mountComponent挂载组件

4. 初始化component,对组件的数据进行赋值和操作

5. 调用设置和渲染的副作用函数

6. 调用了副作用函数effect()

7. renderComponentRoot,对template进行渲染

8. 把subTree子树的VNode挂载到container上,调用patch()

9. 处理DOM元素,比如div/button/span(每个子树subtree)

10. 如果还有子元素,进行patch之后,进行挂载

11.12.13. 处理子节点,进行挂载

Vue.createApp(App).mount('#app')执行过程

1.创建app入口

来到runtime-dom>src>index.ts文件

// 创建app入口
export const createApp = ((...args) => {
  // 创建app使用渲染器ensureRenderer()
  // 渲染器有返回createApp属性，createApp调用之后返回app
  const app = ensureRenderer().createApp(...args)

  if (__DEV__) {
    injectNativeTagCheck(app)
    injectCompilerOptionsCheck(app)
  }
// 从app取出mount
  const { mount } = app
  // 将app.mount函数进行重写，函数原本传入属性，而我们传入‘#app’字符串
  // 重写mount函数是为了跨平台
  app.mount = (containerOrSelector: Element | ShadowRoot | string): any => {
    // normalizeContainer通过querySelector获取到container对象
    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.
      // 原因：在 DOM 模板中可能执行 JS 表达式。
      // 用户必须确保 DOM 模板是受信任的。如果是
      // 由服务器呈现，模板不应包含任何用户数据。
      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
    // 先清空container中的原本内容
    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>

2.render函数

来到runtime-core>src>renderer.ts文件

// render函数传入baseCreatoRenderer()的返回值中
  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 internals: RendererInternals = {
    p: patch,
    um: unmount,
    m: move,
    r: remove,
    mt: mountComponent,
    mc: mountChildren,
    pc: patchChildren,
    pbc: patchBlockChildren,
    n: getNextHostNode,
    o: options
  }

  let hydrate: ReturnType<typeof createHydrationFunctions>[0] | undefined
  let hydrateNode: ReturnType<typeof createHydrationFunctions>[1] | undefined
  if (createHydrationFns) {
    ;[hydrate, hydrateNode] = createHydrationFns(
      internals as RendererInternals<Node, Element>
    )
  }
  // baseCreatoRenderer()返回 createApp
  return {
    render,
    hydrate,//ssr服务端错误
    // createAppAPI函数使用了柯里化
    createApp: createAppAPI(render, hydrate)
  }
}

3.返回app

来到runtime-core>src>apiCreateApp.ts文件

// createApp最终返回createAppAPI() 返回app对象
export function createAppAPI<HostElement>(
  render: RootRenderFunction,
  hydrate?: RootHydrateFunction
): CreateAppFunction<HostElement> {
  // 返回createApp
  return function createApp(rootComponent, rootProps = null) {
    if (!isFunction(rootComponent)) {
      rootComponent = { ...rootComponent }
    }

    if (rootProps != null && !isObject(rootProps)) {
      __DEV__ && warn(`root props passed to app.mount() must be an object.`)
      rootProps = null
    }

    const context = createAppContext()
    const installedPlugins = new Set()

    let isMounted = false
// app对象 app.mixin.directive.comoinebt 创建一个app对象
    const app: App = (context.app = {
      _uid: uid++,
      _component: rootComponent as ConcreteComponent,
      _props: rootProps,
      _container: null,
      _context: context,
      _instance: null,

      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[]) {
        if (installedPlugins.has(plugin)) {
          __DEV__ && warn(`Plugin has already been applied to target app.`)
        } else if (plugin && isFunction(plugin.install)) {
          installedPlugins.add(plugin)
          plugin.install(app, ...options)
        } else if (isFunction(plugin)) {
          installedPlugins.add(plugin)
          plugin(app, ...options)
        } else if (__DEV__) {
          warn(
            `A plugin must either be a function or an object with an "install" ` +
              `function.`
          )
        }
        return app
      },

      mixin(mixin: ComponentOptions) {
        if (__FEATURE_OPTIONS_API__) {
          if (!context.mixins.includes(mixin)) {
            context.mixins.push(mixin)
          } else if (__DEV__) {
            warn(
              'Mixin has already been applied to target app' +
                (mixin.name ? `: ${mixin.name}` : '')
            )
          }
        } else if (__DEV__) {
          warn('Mixins are only available in builds supporting Options API')
        }
        return app
      },

      component(name: string, component?: Component): any {
        if (__DEV__) {
          validateComponentName(name, context.config)
        }
        if (!component) {
          return context.components[name]
        }
        if (__DEV__ && context.components[name]) {
          warn(`Component "${name}" has already been registered in target app.`)
        }
        context.components[name] = component
        return app
      },

      directive(name: string, directive?: Directive) {
        if (__DEV__) {
          validateDirectiveName(name)
        }

        if (!directive) {
          return context.directives[name] as any
        }
        if (__DEV__ && context.directives[name]) {
          warn(`Directive "${name}" has already been registered in target app.`)
        }
        context.directives[name] = directive
        return app
      },

      mount(
        rootContainer: HostElement,
        isHydrate?: boolean,
        isSVG?: boolean
      ): any {
        if (!isMounted) {
          // #5571
          if (__DEV__ && (rootContainer as any).__vue_app__) {
            warn(
              `There is already an app instance mounted on the host container.\n` +
                ` If you want to mount another app on the same host container,` +
                ` you need to unmount the previous app by calling \`app.unmount()\` first.`
            )
          }
          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 getExposeProxy(vnode.component!) || 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)\``
          )
        }
      },

      unmount() {
        if (isMounted) {
          render(null, app._container)
          if (__DEV__ || __FEATURE_PROD_DEVTOOLS__) {
            app._instance = null
            devtoolsUnmountApp(app)
          }
          delete app._container.__vue_app__
        } else if (__DEV__) {
          warn(`Cannot unmount an app that is not mounted.`)
        }
      },

      provide(key, value) {
        if (__DEV__ && (key as string | symbol) in context.provides) {
          warn(
            `App already provides property with key "${String(key)}". ` +
              `It will be overwritten with the new value.`
          )
        }

        context.provides[key as string | symbol] = value

        return app
      }
    })

    if (__COMPAT__) {
      installAppCompatProperties(app, context, render)
    }

    return app
  }
}

mount

来到runtime-core>src>renderer.ts文件

// 如果还有子元素，进行pathch之后，进行挂载
        mountChildren(
          vnode.children as VNodeArrayChildren,
          el,
          null,
          parentComponent,
          parentSuspense,
          isSVG && type !== 'foreignObject',
          slotScopeIds,
          optimized
        )

const mountChildren: MountChildrenFn = (
    children,
    container,
    anchor,
    parentComponent,
    parentSuspense,
    isSVG,
    slotScopeIds,
    optimized,
    start = 0
  ) => {
    // 12.对子节点进行遍历
    for (let i = start; i < children.length; i++) {
      const child = (children[i] = optimized
        ? cloneIfMounted(children[i] as VNode)
        : normalizeVNode(children[i]))
        // 13。遍历后进行挂载
      patch(
        null,
        child,
        container,
        anchor,
        parentComponent,
        parentSuspense,
        isSVG,
        slotScopeIds,
        optimized
      )
    }
  }

//片段只能有数组子级 因为它们要么由编译器生成，要么隐式创建 从数组。 
      // 拿到fragment的所有根组件，拿到子树元素，进行挂载
      mountChildren(
        // n2.children所有的子元素
        n2.children as VNodeArrayChildren,
        container,
        fragmentEndAnchor,
        parentComponent,
        parentSuspense,
        isSVG,
        slotScopeIds,
        optimized
      )

创建流程图：

App组件的挂载和渲染过程

大致分为13步,具体如下：

1. patch:进行diff算法.

// 注意：此闭包中的函数应使用 'const xxx = （） => {}'
  // 样式，以防止被小写器内联。
  // patch:进行diff算法，crateApp->vnode->element
  const patch: PatchFn = (
    n1,//旧的vnode，n1为空，进行挂载
    n2,//新的vnode,n2与n1不同时，进行patch（diff算法）
    container,//patch或mount之后，将vnode挂载到container上
    anchor = null,
    parentComponent = null,
    parentSuspense = null,
    isSVG = false,
    slotScopeIds = null,
    optimized = __DEV__ && isHmrUpdating ? false : !!n2.dynamicChildren
  ) => {

2. 处理组件节点.

} else if (shapeFlag & ShapeFlags.COMPONENT) {
          // 处理组件节点，vnode-><HelloWorld> 按组件进行处理
          processComponent(
            n1,
            n2,
            container,
            anchor,
            parentComponent,
            parentSuspense,
            isSVG,
            slotScopeIds,
            optimized
          )
        }

进入processComponent

// 处理组件类型节点
  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
  ) => {

3. 调用mountComponent挂载组件

// 调用mountComponent挂载组件
        mountComponent(
          n2,
          container,
          anchor,
          parentComponent,
          parentSuspense,
          isSVG,
          optimized
        )
      }

4. 初始化component,对组件的数据进行赋值和操作

// 初始化component,对组件的数据进行赋值和操作
      // setup组件实例，对组件的props/emits/slots/data进行初始化
      setupComponent(instance)//执行完之后组件啥都有了
      if (__DEV__) {
        endMeasure(instance, `init`)
      }
    }

    // setup() is async. This component relies on async logic to be resolved
    // before proceeding
//     setup（） 是异步的。此组件依赖于要解析的异步逻辑
//      在继续之前 
    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
    }

5. 调用设置和渲染的副作用函数

// 调用设置和渲染的副作用函数
    setupRenderEffect(
      instance,
      initialVNode,
      container,
      anchor,
      parentSuspense,
      isSVG,
      optimized
    )

副作用函数

// 副作用函数
  const setupRenderEffect: SetupRenderEffectFn = (
    instance,
    initialVNode,
    container,
    anchor,
    parentSuspense,
    isSVG,
    optimized
  ) => {

6. 调用了副作用函数effect()

// 调用了副作用函数effect()他来着reactive响应式系统，使用响应式数据时，默认进行依赖收集，进行再次执行
    const update: SchedulerJob = (instance.update = () => effect.run())
    update.id = instance.uid
    // allowRecurse
    // #1801, #2043 component render effects should allow recursive updates
                    //组件渲染效果应允许递归更新
    toggleRecurse(instance, true)

    if (__DEV__) {
      effect.onTrack = instance.rtc
        ? e => invokeArrayFns(instance.rtc!, e)
        : void 0
      effect.onTrigger = instance.rtg
        ? e => invokeArrayFns(instance.rtg!, e)
        : void 0
      update.ownerInstance = instance
    }

7. renderComponentRoot,对template进行渲染

// 7. renderComponentRoot,对template进行渲染
            // subTree是template里面的子树，子树被<Fragment>包裹
            instance.subTree = renderComponentRoot(instance)
            if (__DEV__) {
              endMeasure(instance, `render`)
            }
            if (__DEV__) {
              startMeasure(instance, `hydrate`)
            }

8. 把subTree子树的VNode挂载到container上,调用patch()

// 8. 把subTree子树的VNode挂载到container上,调用patch()
          patch(
            null,//因为是挂载所以是null
            subTree,
            container,
            anchor,
            instance,
            parentSuspense,
            isSVG
          )

9. 处理DOM元素,比如div/button/span(每个子树subtree)

// 9. 处理DOM元素,比如div/button/span(每个子树subtree)
        if (shapeFlag & ShapeFlags.ELEMENT) {
          processElement(
            n1,
            n2,
            container,
            anchor,
            parentComponent,
            parentSuspense,
            isSVG,
            slotScopeIds,
            optimized
          )

进入processElement

// 如果template的根元素是div
  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) {
      // 调用mountElement进行挂载元素
      mountElement(
        n2,
        container,
        anchor,
        parentComponent,
        parentSuspense,
        isSVG,
        slotScopeIds,
        optimized
      )
    } else {

10. 如果还有子元素,进行patch之后,进行挂载

} else if (shapeFlag & ShapeFlags.ARRAY_CHILDREN) {
      // 如果还有子元素，进行pathch之后，进行挂载
        mountChildren(
          vnode.children as VNodeArrayChildren,
          el,
          null,
          parentComponent,
          parentSuspense,
          isSVG && type !== 'foreignObject',
          slotScopeIds,
          optimized
        )
      }

11.12.13. 处理子节点,进行挂载

// 11.挂载子节点
  const mountChildren: MountChildrenFn = (
    children,
    container,
    anchor,
    parentComponent,
    parentSuspense,
    isSVG,
    slotScopeIds,
    optimized,
    start = 0
  ) => {
    // 12.对子节点进行遍历
    for (let i = start; i < children.length; i++) {
      const child = (children[i] = optimized
        ? cloneIfMounted(children[i] as VNode)
        : normalizeVNode(children[i]))
        // 13。遍历后进行挂载
      patch(
        null,
        child,
        container,
        anchor,
        parentComponent,
        parentSuspense,
        isSVG,
        slotScopeIds,
        optimized
      )
    }
  }

最后给大家找了个流程图方便大家理解：

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