首次加载(Vue 引入)

前言

Vue 在代码中引入使用前，会主要通过两步生成Vue构造函数：1.创建 Vue 构造函数，2.添加原型方法和属性，3.添加私有方法和属性

• 工程项目中引入之前vue内部会创建一个 Vue 的构造函数

  import Vue from "vue"
  

1.Vue 类

• new vue时进入这里进行组件的初始化操作，调用访问各种准备好的属性和方法

• /src/vue/src/core/instance/index.ts

function Vue(options) {
  if (__DEV__ && !(this instanceof Vue)) {
    warn('Vue is a constructor and should be called with the `new` keyword')
  }
  this._init(options)
}

2.原型扩展

• /src/vue/src/core/instance/index.ts

//@ts-expect-error Vue has function type
initMixin(Vue)
//@ts-expect-error Vue has function type
stateMixin(Vue)
//@ts-expect-error Vue has function type
eventsMixin(Vue)
//@ts-expect-error Vue has function type
lifecycleMixin(Vue)
//@ts-expect-error Vue has function type
renderMixin(Vue)

2.1 initMixin

• 初始化时在原型上混入初始化函数，当实例化 Vue 时，会调用初始化方法，从而依次执行里面的相关属性和方法。

• /src/vue/src/core/instance/init.ts

export function initMixin(Vue: typeof Component) {
  Vue.prototype._init = function (options?: Record<string, any>) {
    const vm: Component = this
    // a uid
    vm._uid = uid++

    let startTag, endTag
    /* istanbul ignore if */
    if (__DEV__ && config.performance && mark) {
      startTag = `vue-perf-start:${vm._uid}`
      endTag = `vue-perf-end:${vm._uid}`
      mark(startTag)
    }

    // a flag to mark this as a Vue instance without having to do instanceof
    // check
    vm._isVue = true
    // avoid instances from being observed
    vm.__v_skip = true
    // effect scope
    vm._scope = new EffectScope(true /* detached */)
    vm._scope._vm = true
    // merge options
    if (options && options._isComponent) {
      // optimize internal component instantiation
      // since dynamic options merging is pretty slow, and none of the
      // internal component options needs special treatment.
      initInternalComponent(vm, options as any)
    } else {
      vm.$options = mergeOptions(
        resolveConstructorOptions(vm.constructor as any),
        options || {},
        vm
      )
    }
    /* istanbul ignore else */
    if (__DEV__) {
      initProxy(vm)
    } else {
      vm._renderProxy = vm
    }
    // expose real self
    vm._self = vm
    initLifecycle(vm)
    initEvents(vm)
    initRender(vm)
    callHook(vm, 'beforeCreate', undefined, false /* setContext */)
    initInjections(vm) // resolve injections before data/props
    initState(vm)
    initProvide(vm) // resolve provide after data/props
    callHook(vm, 'created')

    /* istanbul ignore if */
    if (__DEV__ && config.performance && mark) {
      vm._name = formatComponentName(vm, false)
      mark(endTag)
      measure(`vue ${vm._name} init`, startTag, endTag)
    }

    if (vm.$options.el) {
      vm.$mount(vm.$options.el)
    }
  }
}

2.2 stateMixin

• Vue 初始化时，在 Vue 的原型上添加响应式相关的函数，在 Vue 运行时内部 this 可以调用相关原型上的方法

• /src/vue/src/core/instance/state.ts

export function stateMixin(Vue: typeof Component) {
  // flow somehow has problems with directly declared definition object
  // when using Object.defineProperty, so we have to procedurally build up
  // the object here.
  const dataDef: any = {}
  dataDef.get = function () {
    return this._data
  }
  const propsDef: any = {}
  propsDef.get = function () {
    return this._props
  }
  if (__DEV__) {
    dataDef.set = function () {
      warn(
        'Avoid replacing instance root $data. ' +
          'Use nested data properties instead.',
        this
      )
    }
    propsDef.set = function () {
      warn(`$props is readonly.`, this)
    }
  }
  Object.defineProperty(Vue.prototype, '$data', dataDef)
  Object.defineProperty(Vue.prototype, '$props', propsDef)

  Vue.prototype.$set = set
  Vue.prototype.$delete = del
  Vue.prototype.$watch = function (
    expOrFn: string | (() => any),
    cb: any,
    options?: Record<string, any>
  ): Function {
    const vm: Component = this
    if (isPlainObject(cb)) {
      return createWatcher(vm, expOrFn, cb, options)
    }
    options = options || {}
    options.user = true
    const watcher = new Watcher(vm, expOrFn, cb, options)
    if (options.immediate) {
      const info = `callback for immediate watcher "${watcher.expression}"`
      pushTarget()
      invokeWithErrorHandling(cb, vm, [watcher.value], vm, info)
      popTarget()
    }
    return function unwatchFn() {
      watcher.teardown()
    }
  }
}

2.3 eventsMixin

• 初始化时，在 Vue 原型上扩展相关的事件方法

• /src/vue/src/core/instance/events.ts

export function eventsMixin(Vue: typeof Component) {
  const hookRE = /^hook:/
  Vue.prototype.$on = function (
    event: string | Array<string>,
    fn: Function
  ): Component {
    const vm: Component = this
    if (isArray(event)) {
      for (let i = 0, l = event.length; i < l; i++) {
        vm.$on(event[i], fn)
      }
    } else {
      ;(vm._events[event] || (vm._events[event] = [])).push(fn)
      // optimize hook:event cost by using a boolean flag marked at registration
      // instead of a hash lookup
      if (hookRE.test(event)) {
        vm._hasHookEvent = true
      }
    }
    return vm
  }

  Vue.prototype.$once = function (event: string, fn: Function): Component {
    const vm: Component = this
    function on() {
      vm.$off(event, on)
      fn.apply(vm, arguments)
    }
    on.fn = fn
    vm.$on(event, on)
    return vm
  }

  Vue.prototype.$off = function (
    event?: string | Array<string>,
    fn?: Function
  ): Component {
    const vm: Component = this
    // all
    if (!arguments.length) {
      vm._events = Object.create(null)
      return vm
    }
    // array of events
    if (isArray(event)) {
      for (let i = 0, l = event.length; i < l; i++) {
        vm.$off(event[i], fn)
      }
      return vm
    }
    // specific event
    const cbs = vm._events[event!]
    if (!cbs) {
      return vm
    }
    if (!fn) {
      vm._events[event!] = null
      return vm
    }
    // specific handler
    let cb
    let i = cbs.length
    while (i--) {
      cb = cbs[i]
      if (cb === fn || cb.fn === fn) {
        cbs.splice(i, 1)
        break
      }
    }
    return vm
  }

  Vue.prototype.$emit = function (event: string): Component {
    const vm: Component = this
    if (__DEV__) {
      const lowerCaseEvent = event.toLowerCase()
      if (lowerCaseEvent !== event && vm._events[lowerCaseEvent]) {
        tip(
          `Event "${lowerCaseEvent}" is emitted in component ` +
            `${formatComponentName(
              vm
            )} but the handler is registered for "${event}". ` +
            `Note that HTML attributes are case-insensitive and you cannot use ` +
            `v-on to listen to camelCase events when using in-DOM templates. ` +
            `You should probably use "${hyphenate(
              event
            )}" instead of "${event}".`
        )
      }
    }
    let cbs = vm._events[event]
    if (cbs) {
      cbs = cbs.length > 1 ? toArray(cbs) : cbs
      const args = toArray(arguments, 1)
      const info = `event handler for "${event}"`
      for (let i = 0, l = cbs.length; i < l; i++) {
        invokeWithErrorHandling(cbs[i], vm, args, vm, info)
      }
    }
    return vm
  }
}

2.4 lifecycleMixin

• 初始化时在原型上扩展相关生命周期的方法，可以在 Vue 运行时 this 上使用

• /src/vue/src/core/instance/lifecycle.ts

export function lifecycleMixin(Vue: typeof Component) {
  Vue.prototype._update = function (vnode: VNode, hydrating?: boolean) {
    const vm: Component = this
    const prevEl = vm.$el
    const prevVnode = vm._vnode
    const restoreActiveInstance = setActiveInstance(vm)
    vm._vnode = vnode
    // Vue.prototype.__patch__ is injected in entry points
    // based on the rendering backend used.
    if (!prevVnode) {
      // initial render
      vm.$el = vm.__patch__(vm.$el, vnode, hydrating, false /* removeOnly */)
    } else {
      // updates
      vm.$el = vm.__patch__(prevVnode, vnode)
    }
    restoreActiveInstance()
    // update __vue__ reference
    if (prevEl) {
      prevEl.__vue__ = null
    }
    if (vm.$el) {
      vm.$el.__vue__ = vm
    }
    // if parent is an HOC, update its $el as well
    let wrapper: Component | undefined = vm
    while (
      wrapper &&
      wrapper.$vnode &&
      wrapper.$parent &&
      wrapper.$vnode === wrapper.$parent._vnode
    ) {
      wrapper.$parent.$el = wrapper.$el
      wrapper = wrapper.$parent
    }
    // updated hook is called by the scheduler to ensure that children are
    // updated in a parent's updated hook.
  }
  Vue.prototype.$forceUpdate = function () {
    const vm: Component = this
    if (vm._watcher) {
      vm._watcher.update()
    }
  }
  Vue.prototype.$destroy = function () {
    const vm: Component = this
    if (vm._isBeingDestroyed) {
      return
    }
    callHook(vm, 'beforeDestroy')
    vm._isBeingDestroyed = true
    // remove self from parent
    const parent = vm.$parent
    if (parent && !parent._isBeingDestroyed && !vm.$options.abstract) {
      remove(parent.$children, vm)
    }
    // teardown scope. this includes both the render watcher and other
    // watchers created
    vm._scope.stop()
    // remove reference from data ob
    // frozen object may not have observer.
    if (vm._data.__ob__) {
      vm._data.__ob__.vmCount--
    }
    // call the last hook...
    vm._isDestroyed = true
    // invoke destroy hooks on current rendered tree
    vm.__patch__(vm._vnode, null)
    // fire destroyed hook
    callHook(vm, 'destroyed')
    // turn off all instance listeners.
    vm.$off()
    // remove __vue__ reference
    if (vm.$el) {
      vm.$el.__vue__ = null
    }
    // release circular reference (#6759)
    if (vm.$vnode) {
      vm.$vnode.parent = null
    }
  }
}

2.5 renderMixin

• Vue 初始化时在原型上扩展渲染相关的函数，可以在 Vue 运行时在 this 上访问这些方法

• /src/vue/src/core/instance/render.ts

export function renderMixin(Vue: typeof Component) {
  // install runtime convenience helpers
  installRenderHelpers(Vue.prototype)

  Vue.prototype.$nextTick = function (fn: (...args: any[]) => any) {
    return nextTick(fn, this)
  }
  Vue.prototype._render = function (): VNode {
    const vm: Component = this
    const { render, _parentVnode } = vm.$options

    if (_parentVnode && vm._isMounted) {
      vm.$scopedSlots = normalizeScopedSlots(
        vm.$parent!,
        _parentVnode.data!.scopedSlots,
        vm.$slots,
        vm.$scopedSlots
      )
      if (vm._slotsProxy) {
        syncSetupSlots(vm._slotsProxy, vm.$scopedSlots)
      }
    }

    // set parent vnode. this allows render functions to have access
    // to the data on the placeholder node.
    vm.$vnode = _parentVnode!
    // render self
    let vnode
    try {
      // There's no need to maintain a stack because all render fns are called
      // separately from one another. Nested component's render fns are called
      // when parent component is patched.
      setCurrentInstance(vm)
      currentRenderingInstance = vm
      vnode = render.call(vm._renderProxy, vm.$createElement)
    } catch (e: any) {
      handleError(e, vm, `render`)
      // return error render result,
      // or previous vnode to prevent render error causing blank component
      /* istanbul ignore else */
      if (__DEV__ && vm.$options.renderError) {
        try {
          vnode = vm.$options.renderError.call(
            vm._renderProxy,
            vm.$createElement,
            e
          )
        } catch (e: any) {
          handleError(e, vm, `renderError`)
          vnode = vm._vnode
        }
      } else {
        vnode = vm._vnode
      }
    } finally {
      currentRenderingInstance = null
      setCurrentInstance()
    }
    // if the returned array contains only a single node, allow it
    if (isArray(vnode) && vnode.length === 1) {
      vnode = vnode[0]
    }
    // return empty vnode in case the render function errored out
    if (!(vnode instanceof VNode)) {
      if (__DEV__ && isArray(vnode)) {
        warn(
          'Multiple root nodes returned from render function. Render function ' +
            'should return a single root node.',
          vm
        )
      }
      vnode = createEmptyVNode()
    }
    // set parent
    vnode.parent = _parentVnode
    return vnode
  }
}

3.私有扩展

• 通过initGlobalAPI(Vue)实现在 Vue 上添加私有属性和方法

• /src/vue/src/core/index.ts

import Vue from './instance/index'
import { initGlobalAPI } from './global-api/index'
import { isServerRendering } from 'core/util/env'
import { FunctionalRenderContext } from 'core/vdom/create-functional-component'
import { version } from 'v3'

initGlobalAPI(Vue)

Object.defineProperty(Vue.prototype, '$isServer', {
  get: isServerRendering
})

Object.defineProperty(Vue.prototype, '$ssrContext', {
  get() {
    /* istanbul ignore next */
    return this.$vnode && this.$vnode.ssrContext
  }
})

// expose FunctionalRenderContext for ssr runtime helper installation
Object.defineProperty(Vue, 'FunctionalRenderContext', {
  value: FunctionalRenderContext
})

Vue.version = version

export default Vue

• initGlobalAPI函数

• /src/vue/src/core/global-api/index.ts

export function initGlobalAPI(Vue: GlobalAPI) {
  // config
  const configDef: Record<string, any> = {}
  configDef.get = () => config
  if (__DEV__) {
    configDef.set = () => {
      warn(
        'Do not replace the Vue.config object, set individual fields instead.'
      )
    }
  }
  Object.defineProperty(Vue, 'config', configDef)

  // exposed util methods.
  // NOTE: these are not considered part of the public API - avoid relying on
  // them unless you are aware of the risk.
  Vue.util = {
    warn,
    extend,
    mergeOptions,
    defineReactive
  }

  Vue.set = set
  Vue.delete = del
  Vue.nextTick = nextTick

  // 2.6 explicit observable API
  Vue.observable = <T>(obj: T): T => {
    observe(obj)
    return obj
  }

  Vue.options = Object.create(null)
  ASSET_TYPES.forEach(type => {
    Vue.options[type + 's'] = Object.create(null)
  })

  // this is used to identify the "base" constructor to extend all plain-object
  // components with in Weex's multi-instance scenarios.
  Vue.options._base = Vue

  extend(Vue.options.components, builtInComponents)

  initUse(Vue)
  initMixin(Vue)
  initExtend(Vue)
  initAssetRegisters(Vue)
}

3.1 initUse

提示

在 Vue 上添加私有方法：initUse 加载插件

• /src/vue/src/core/global-api/use.ts

export function initUse(Vue: GlobalAPI) {
  Vue.use = function (plugin: Function | any) {
    const installedPlugins =
      this._installedPlugins || (this._installedPlugins = [])
    if (installedPlugins.indexOf(plugin) > -1) {
      return this
    }

    // additional parameters
    const args = toArray(arguments, 1)
    args.unshift(this)
    if (isFunction(plugin.install)) {
      plugin.install.apply(plugin, args)
    } else if (isFunction(plugin)) {
      plugin.apply(null, args)
    }
    installedPlugins.push(plugin)
    return this
  }
}

3.2 initMixin

• /src/vue/src/core/global-api/mixin.ts

export function initMixin(Vue: GlobalAPI) {
  Vue.mixin = function (mixin: Object) {
    this.options = mergeOptions(this.options, mixin)
    return this
  }
}

3.3 initExtend

提示

在 Vue 上添加私有方法：extend 继承子类

• /src/vue/src/core/global-api/extend.ts

export function initExtend(Vue: GlobalAPI) {
  /**
   * Each instance constructor, including Vue, has a unique
   * cid. This enables us to create wrapped "child
   * constructors" for prototypal inheritance and cache them.
   */
  Vue.cid = 0
  let cid = 1

  /**
   * Class inheritance
   */
  Vue.extend = function (extendOptions: any): typeof Component {
    extendOptions = extendOptions || {}
    const Super = this
    const SuperId = Super.cid
    const cachedCtors = extendOptions._Ctor || (extendOptions._Ctor = {})
    if (cachedCtors[SuperId]) {
      return cachedCtors[SuperId]
    }

    const name =
      getComponentName(extendOptions) || getComponentName(Super.options)
    if (__DEV__ && name) {
      validateComponentName(name)
    }

    const Sub = function VueComponent(this: any, options: any) {
      this._init(options)
    } as unknown as typeof Component
    Sub.prototype = Object.create(Super.prototype)
    Sub.prototype.constructor = Sub
    Sub.cid = cid++
    Sub.options = mergeOptions(Super.options, extendOptions)
    Sub['super'] = Super

    // For props and computed properties, we define the proxy getters on
    // the Vue instances at extension time, on the extended prototype. This
    // avoids Object.defineProperty calls for each instance created.
    if (Sub.options.props) {
      initProps(Sub)
    }
    if (Sub.options.computed) {
      initComputed(Sub)
    }

    // allow further extension/mixin/plugin usage
    Sub.extend = Super.extend
    Sub.mixin = Super.mixin
    Sub.use = Super.use

    // create asset registers, so extended classes
    // can have their private assets too.
    ASSET_TYPES.forEach(function (type) {
      Sub[type] = Super[type]
    })
    // enable recursive self-lookup
    if (name) {
      Sub.options.components[name] = Sub
    }

    // keep a reference to the super options at extension time.
    // later at instantiation we can check if Super's options have
    // been updated.
    Sub.superOptions = Super.options
    Sub.extendOptions = extendOptions
    Sub.sealedOptions = extend({}, Sub.options)

    // cache constructor
    cachedCtors[SuperId] = Sub
    return Sub
  }
}

3.4 initAssetRegisters

提示

在 Vue 上添加私有方法：component、directive、filter

• /src/vue/src/core/global-api/assets.ts

export function initAssetRegisters(Vue: GlobalAPI) {
  /**
   * Create asset registration methods.
   */
  ASSET_TYPES.forEach(type => {
    // @ts-expect-error function is not exact same type
    Vue[type] = function (
      id: string,
      definition?: Function | Object
    ): Function | Object | void {
      if (!definition) {
        return this.options[type + 's'][id]
      } else {
        /* istanbul ignore if */
        if (__DEV__ && type === 'component') {
          validateComponentName(id)
        }
        if (type === 'component' && isPlainObject(definition)) {
          // @ts-expect-error
          definition.name = definition.name || id
          definition = this.options._base.extend(definition)
        }
        if (type === 'directive' && isFunction(definition)) {
          definition = { bind: definition, update: definition }
        }
        this.options[type + 's'][id] = definition
        return definition
      }
    }
  })
}

4.其他

• 添加挂载函数，重写挂载函数
• 添加编译函数

4.1 $mount

• /src/vue/src/platforms/web/runtime/index.ts

Vue.prototype.$mount = function (
  el?: string | Element,
  hydrating?: boolean
): Component {
  el = el && inBrowser ? query(el) : undefined
  return mountComponent(this, el, hydrating)
}

• /src/vue/src/platforms/web/runtime-with-compiler.ts

const mount = Vue.prototype.$mount
Vue.prototype.$mount = function (
  el?: string | Element,
  hydrating?: boolean
): Component {
  el = el && query(el)

  /* istanbul ignore if */
  if (el === document.body || el === document.documentElement) {
    __DEV__ &&
      warn(
        `Do not mount Vue to <html> or <body> - mount to normal elements instead.`
      )
    return this
  }

  const options = this.$options
  // resolve template/el and convert to render function
  if (!options.render) {
    let template = options.template
    if (template) {
      if (typeof template === 'string') {
        if (template.charAt(0) === '#') {
          template = idToTemplate(template)
          /* istanbul ignore if */
          if (__DEV__ && !template) {
            warn(
              `Template element not found or is empty: ${options.template}`,
              this
            )
          }
        }
      } else if (template.nodeType) {
        template = template.innerHTML
      } else {
        if (__DEV__) {
          warn('invalid template option:' + template, this)
        }
        return this
      }
    } else if (el) {
      // @ts-expect-error
      template = getOuterHTML(el)
    }
    if (template) {
      /* istanbul ignore if */
      if (__DEV__ && config.performance && mark) {
        mark('compile')
      }

      const { render, staticRenderFns } = compileToFunctions(
        template,
        {
          outputSourceRange: __DEV__,
          shouldDecodeNewlines,
          shouldDecodeNewlinesForHref,
          delimiters: options.delimiters,
          comments: options.comments
        },
        this
      )
      options.render = render
      options.staticRenderFns = staticRenderFns

      /* istanbul ignore if */
      if (__DEV__ && config.performance && mark) {
        mark('compile end')
        measure(`vue ${this._name} compile`, 'compile', 'compile end')
      }
    }
  }
  return mount.call(this, el, hydrating)
}

4.2 compiler

• 使用闭包创建编译函数，存入内存中，下次可以加快编译
• /src/vue/src/platforms/web/runtime-with-compiler.ts

Vue.compile = compileToFunctions

4.3 patch

• 使用闭包创建派发函数，存入内存中，下次可以加快将虚拟 dom 转换为真实 dom
• /src/vue/src/platforms/web/runtime/index.ts

Vue.prototype.__patch__ = inBrowser ? patch : noop