vue3源码理解1

creatApp({}).mount("#app")当我们执行这行代码时，发生了什么
  

packages/runtime-dom/src/index.ts 下的 70行 
//通过ensureRenderer渲染器函数里的createApp函数生成app实例
export const createApp = ((...args) => {
const app = ensureRenderer().createApp(...args)
...

function ensureRenderer() {   当前文件43行左右
    //单例模式  ，一开始是没有renderer所以会执行后面的createRenderer，创建一个renderer
    return (
        renderer ||  (renderer = createRenderer<Node, Element | ShadowRoot>(rendererOptions))
    )
}

createRenderer 在packages/runtime-core/src/renderer.ts  
　　//300行左右
    export function createRenderer<
        HostNode = RendererNode,
        HostElement = RendererElement
    >(options: RendererOptions<HostNode, HostElement>) {
        return baseCreateRenderer<HostNode, HostElement>(options)
    }

baseCreateRenderer   327行到2340行左右

然后内部执行了baseCreateRenderer工厂函数，这个函数创建了一个渲染器
baseCreateRenderer 是一个很大的工厂函数，也可以说是vue3里面最大的函数
内部最终结果return 了三个值
return {
    render,//把接收到的vnode转换成dom,并插入到宿主元素上
    hydrate, //用于SSR，服务端将一个vnode转换成html字符串
    createApp: createAppAPI(render, hydrate)  //还记得上面的ensureRenderer().createApp(...args)这个代码吗？就是这里抛出去的
}
render :注意：这是渲染器的渲染函数，而不是组件的渲染函数， 渲染器渲染函数，接收一个虚拟DOM，而不是生产一个虚拟DOM。然后把它转换成这个虚拟DOM对应的真实DOM，转换完成后挂载到#app这个宿主上面

我们可以看到baseCreateRenderer  return 出的createApp是由createAppAPI这个工厂函数返回的，那下面我们去找找createAppAPI是哪里来的
嗯哼，找到了，在这········packages/runtime-core/src/apiCreateApp.ts  177行左右

createAppAPI内部，这才是createApp的终极奥义，生产发源地

export function createAppAPI<HostElement>(
  render: RootRenderFunction,
  hydrate?: RootHydrateFunction
): CreateAppFunction<HostElement> {
  return function createApp(rootComponent, rootProps = null) { //接收两个参数，第一个参数为根节点组件，第二个为配置项
    if (rootProps != null && !isObject(rootProps)) {
      __DEV__ && warn(`root props passed to app.mount() must be an object.`)
      rootProps = null
    }
......

const app: App = (context.app = { //声明App实例

get config() {
    return context.config
  },

  set config(v) {
    ...
  },

  use(plugin: Plugin, ...options: any[]) {
    ...
    return app
  },

  mixin(mixin: ComponentOptions) {
    ....
    return app
  },

  component(name: string, component?: Component): any {
    ...
    return app
  },

  directive(name: string, directive?: Directive) {
    ...
    return app
  },

  mount(//挂载，这是重点
    rootContainer: HostElement, //这里把我们挂载点的html转换成了vnode
    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) //然后执行一个渲染器，这里执行，又回到了上面baseCreateRenderer 函数return 出的那个对象  
      }

      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__) {}
  },

  unmount() {
   ...
  },

  provide(key, value) {
  ...
    return app
  }
}

.....

  return {
    render,
    hydrate,
    createApp: createAppAPI(render, hydrate)，刚刚我们在这工厂函数里的render是这里传进去的，那我们这次去看看render内部
}

render  packages/runtime-core/src/renderer.ts  2309行左右

const render: RootRenderFunction = (vnode, container, isSVG) => {

//首次执行时 参数vnode不为null

  if (vnode == null) {
    if (container._vnode) {
      unmount(container._vnode, null, null, true)
    }
  } else { //所以执行patch,
    patch(//内部就是我们vue的diff了
　　　　container._vnode || null,//老节点 
　　　　 vnode,//新节点，首次执行时，没有老元素
　　　　 container,//宿主元素 
　　　　 null, 
　　　　 null,
　　　　 null, 
　　　　isSVG
　　　)
　　　//patch是一个多功能函数，如果是首次执行，那执行的就是挂载，如果不是那就会执行diff操作
  }
  flushPostFlushCbs()
  container._vnode = vnode
}

pacth  packages/runtime-core/src/renderer.ts  360行左右

const patch: PatchFn = (
  n1, //老节点
  n2, //新节点
  container,
  anchor = null,
  parentComponent = null,
  parentSuspense = null,
  isSVG = false,
  slotScopeIds = null,
  optimized = __DEV__ && isHmrUpdating ? false : !!n2.dynamicChildren
) => {
  if (n1 === n2) { //这里没想通，为啥直接这样比较也行？？
    return
  }

  // 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 //从新节点里面，获取节点类型，然后执行不同的case
  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) {//首次执行的case
        processComponent( //挂载根组件，以后挂载组件也在这
          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)
  }
}