vue3源码学习api-createApp-amount

首先看看vue文档什么是 Vue？

Vue (发音为 /vjuː/，类似 view) 是一款用于构建用户界面的 JavaScript 框架。它基于标准 HTML、CSS 和 JavaScript 构建，并提供了一套声明式的、组件化的编程模型，帮助你高效地开发用户界面。无论是简单还是复杂的界面，Vue 都可以胜任。

下面是一个最基本的示例：

import { createApp, ref } from 'vue'
createApp({
  setup() {
    return {
      count: ref(0)
    }
  }
}).mount('#app')

学习vue 开发都是从这个例子开始学习，在这个例子中涉及了这些api

1 createApp
2 mount
3 ref
4 setup

其中 ref 属于reactivity：反应系统就暂时先不深究了

setup 属于vue3 新的语法糖也先不深究了

就先看看最简单的createApp 和mount

createApp

先看看vue 仓库中的packages/vue/src/index.ts

地址 https://github.com/vuejs/core/blob/main/packages/vue/src/index.ts

export { compileToFunction as compile }
export * from '@vue/runtime-dom'

可以看到到处了一个编译的方法和 @vue/runtime-dom 中的方法

根据上文

runtime-dom：针对浏览器的运行时。包括原生 DOM API、属性、属性、事件处理程序等的处理。

在runtime-dom 包中找到相关的方法

地址 https://github.com/vuejs/core/blob/main/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 !== '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>
function ensureRenderer() {
  return (
    renderer ||
    (renderer = createRenderer<Node, Element | ShadowRoot>(rendererOptions))
  )
}

走查代码可以发现选是创建了一个渲染器Renderer

然后调用了渲染器的方法 createApp

查看具体方法

地址 https://github.com/vuejs/core/blob/main/packages/runtime-core/src/renderer.ts

创建渲染器的方法是一个比较长的方法

里面的很多方法看名称，更多的设计对dom的操作，不过我们还是先关注createApp 干了些什么

function baseCreateRenderer(
  options: RendererOptions,
  createHydrationFns?: typeof createHydrationFunctions
): any {
    ......
  return {
    render,
    hydrate,
    createApp: createAppAPI(render, hydrate)
  }
}

发现createAppAPI 来自apiCreateApp 文件

地址 https://github.com/vuejs/core/blob/main/packages/runtime-core/src/apiCreateApp.ts

import { createAppAPI, CreateAppFunction } from './apiCreateApp'

代码如下

export function createAppAPI<HostElement>(
  render: RootRenderFunction<HostElement>,
  hydrate?: RootHydrateFunction
): CreateAppFunction<HostElement> {
  return function createApp(rootComponent, rootProps = null) {
    if (!isFunction(rootComponent)) {
      rootComponent = extend({}, rootComponent)
    }
    if (rootProps != null && !isObject(rootProps)) {
      __DEV__ && warn(`root props passed to app.mount() must be an object.`)
      rootProps = null
    }
    const context = createAppContext()
    // TODO remove in 3.4
    if (__DEV__) {
      Object.defineProperty(context.config, 'unwrapInjectedRef', {
        get() {
          return true
        },
        set() {
          warn(
            `app.config.unwrapInjectedRef has been deprecated. ` +
              `3.3 now always unwraps injected refs in Options API.`
          )
        }
      })
    }
    const installedPlugins = new WeakSet()
    let isMounted = false
    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, 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
      },
      runWithContext(fn) {
        currentApp = app
        try {
          return fn()
        } finally {
          currentApp = null
        }
      }
    })
    if (__COMPAT__) {
      installAppCompatProperties(app, context, render)
    }
    return app
  }
}

可以发现createApp 的第一个参数是rootComponent

需要传递的是一个组件，作为根组件

第二个参数rootProps是这个给这个组件传递的参数

通过走查文件可以发现一些常用的api 也是出现在这里

例如 use、mixin、component、directive、mount、unmount、provide

我们要找的mount 也是对这里mount的调用

mount

可以看到 mount主要是参数是rootContainer 另外两个是可选参数

在通过createVNode 创建一个vnode 之后

调用getExposeProxy

返回当前刚才创建的vnode的代理

export function getExposeProxy(instance: ComponentInternalInstance) {
  if (instance.exposed) {
    return (
      instance.exposeProxy ||
      (instance.exposeProxy = new Proxy(proxyRefs(markRaw(instance.exposed)), {
        get(target, key: string) {
          if (key in target) {
            return target[key]
          } else if (key in publicPropertiesMap) {
            return publicPropertiesMap[key](instance)
          }
        },
        has(target, key: string) {
          return key in target || key in publicPropertiesMap
        }
      }))
    )
  }
}

代码中实际调用的mount

依然在createAppAPI 里面这里的传参更友好了可以传入Selector 方便选择dom节点

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
  }