Vue源码分析之Vue实例初始化详解

export function initLifecycle (vm: Component) {
 const options = vm.$options

 // locate first non-abstract parent
 let parent = options.parent
 if (parent && !options.abstract) {
  while (parent.$options.abstract && parent.$parent) {
   parent = parent.$parent
  }
  parent.$children.push(vm) // 自己把自己添加到父级的$children数组中
 }

 vm.$parent = parent // 父组件实例
 vm.$root = parent ? parent.$root : vm // 根组件 如果不存在父组件，则本身就是根组件

 vm.$children = [] // 用来存放子组件
 vm.$refs = {}

 vm._watcher = null 
 vm._inactive = null 
 vm._directInactive = false
 vm._isMounted = false
 vm._isDestroyed = false
 vm._isBeingDestroyed = false
}

// v-on如果写在平台标签上如：div,则会将v-on上注册的事件注册到浏览器事件中
// v-on如果写在组件标签上，则会将v-on注册的事件注册到子组件的事件系统
// 子组件（Vue实例）在初始化的时候，有可能接收到父组件向子组件注册的事件。
// 子组件（Vue实例）自身模板注册的事件，只要在渲染的时候才会根据虚拟DOM的对比结果
// 来确定是注册事件还是解绑事件

// 这里初始化的事件是指父组件在模板中使用v-on注册的事件添加到子组件的事件系统也就是vue的事件系统。
export function initEvents (vm: Component) {
 vm._events = Object.create(null) // 初始化
 vm._hasHookEvent = false
 // init parent attached events 初初始化腹肌组件添加的事件
 const listeners = vm.$options._parentListeners
 if (listeners) {
  updateComponentListeners(vm, listeners)
 }
}

export function updateComponentListeners (
 vm: Component,
 listeners: Object,
 oldListeners: ?Object
) {
 target = vm
 updateListeners(listeners, oldListeners || {}, add, remove, createOnceHandler, vm)
 target = undefined
}

export function initInjections (vm: Component) {
 // 自下而上读取inject
 const result = resolveInject(vm.$options.inject, vm)
 if (result) {
  // 设置为false 避免defineReactive函数把数据转换为响应式
  toggleObserving(false)
  Object.keys(result).forEach(key => {
    defineReactive(vm, key, result[key])
  })
  // 再次更改回来
  toggleObserving(true)
 }
}

export function resolveInject (inject: any, vm: Component): ?Object {
 if (inject) {
  // inject is :any because flow is not smart enough to figure out cached
  const result = Object.create(null)
  // 如果浏览器支持Symbol,则使用Reflect.ownkyes(),否则使用Object.keys()
  const keys = hasSymbol
   ? Reflect.ownKeys(inject)
   : Object.keys(inject)

  for (let i = 0; i < keys.length; i++) {
   const key = keys[i]
   // #6574 in case the inject object is observed...
   if (key === '__ob__') continue
   const provideKey = inject[key].from
   let source = vm
   // 当provided注入内容的时候就是把内容注入到当前实例的_provided中
   // 刚开始的时候 source就是实本身，挡在source._provided中找不到对应的值
   // 就会把source设置为父实例
   // Vue实例化的第一步就是规格化用户传入的数据，所以inject不管时数组还是对象
   // 最后都会变成对象
   while (source) {
    if (source._provided && hasOwn(source._provided, provideKey)) {
     result[key] = source._provided[provideKey]
     break
    }
    source = source.$parent
   }
   // 处理默认值的情况
   if (!source) {
    if ('default' in inject[key]) {
     const provideDefault = inject[key].default
     result[key] = typeof provideDefault === 'function'
      ? provideDefault.call(vm)
      : provideDefault
    } else if (process.env.NODE_ENV !== 'production') {
     warn(`Injection "${key}" not found`, vm)
    }
   }
  }
  return result
 }
}

export function initState (vm: Component) {
 vm._watchers = []
 // 获取到经过初始化的用户传进来的options
 const opts = vm.$options
 if (opts.props) initProps(vm, opts.props)
 if (opts.methods) initMethods(vm, opts.methods)
 if (opts.data) {
  initData(vm)
 } else {
  observe(vm._data = {}, true /* asRootData */)
 }
 if (opts.computed) initComputed(vm, opts.computed)
 if (opts.watch && opts.watch !== nativeWatch) {
  initWatch(vm, opts.watch)
 }
}

function initProps (vm: Component, propsOptions: Object) {
 const propsData = vm.$options.propsData || {}
 const props = vm._props = {}
 // cache prop keys so that future props updates can iterate using Array
 // instead of dynamic object key enumeration.
 // 缓存props的key值
 const keys = vm.$options._propKeys = []
 const isRoot = !vm.$parent
 // root instance props should be converted
 // 如果不是跟组件则没必要转换成响应式数据
 if (!isRoot) {
  // 控制是否转换成响应式数据
  toggleObserving(false)
 }
 for (const key in propsOptions) {
  keys.push(key)
  // 获取props的值
  const value = validateProp(key, propsOptions, propsData, vm)
  defineReactive(props, key, value)
  // static props are already proxied on the component's prototype
  // during Vue.extend(). We only need to proxy props defined at
  // instantiation here.
  // 把props代理到Vue实例上来，可以直接通过this.props访问
  if (!(key in vm)) {
   proxy(vm, `_props`, key)
  }
 }
 toggleObserving(true)
}

function initMethods (vm: Component, methods: Object) {
 const props = vm.$options.props
 for (const key in methods) {
  if (process.env.NODE_ENV !== 'production') {
   // 如果key不是一个函数 报错
   if (typeof methods[key] !== 'function') {
    warn(
     `Method "${key}" has type "${typeof methods[key]}" in the component definition. ` +
     `Did you reference the function correctly?`,
     vm
    )
   }
   // 如果props中存在同名的属性 报错
   if (props && hasOwn(props, key)) {
    warn(
     `Method "${key}" has already been defined as a prop.`,
     vm
    )
   }
   // isReserved判断是否以$或_开头
   if ((key in vm) && isReserved(key)) {
    warn(
     `Method "${key}" conflicts with an existing Vue instance method. ` +
     `Avoid defining component methods that start with _ or $.`
    )
   }
  }
  // 把methods的方法绑定到Vue实例上
  vm[key] = typeof methods[key] !== 'function' ? noop : bind(methods[key], vm)
 }
}

function initData (vm: Component) {
 let data = vm.$options.data
 data = vm._data = typeof data === 'function'
  ? getData(data, vm)
  : data || {}
 // isPlainObject监测data是不是对象
 if (!isPlainObject(data)) {
  data = {}
  process.env.NODE_ENV !== 'production' && warn(
   'data functions should return an object:\n' +
   'https://vuejs.org/v2/guide/components.html#data-Must-Be-a-Function',
   vm
  )
 }
 // proxy data on instance
 const keys = Object.keys(data)
 const props = vm.$options.props
 const methods = vm.$options.methods
 let i = keys.length
 // 循环data
 while (i--) {
  const key = keys[i]
  if (process.env.NODE_ENV !== 'production') {
   // 如果在methods中存在和key同名的属性 则报错
   if (methods && hasOwn(methods, key)) {
    warn(
     `Method "${key}" has already been defined as a data property.`,
     vm
    )
   }
  }
  // 如果在props中存在和key同名的属性 则报错
  if (props && hasOwn(props, key)) {
   process.env.NODE_ENV !== 'production' && warn(
    `The data property "${key}" is already declared as a prop. ` +
    `Use prop default value instead.`,
    vm
   )
  } else if (!isReserved(key)) {
   // isReserved判断是否以$或_开头
   // 代理data，使得可以直接通过this.key访问this._data.key
   proxy(vm, `_data`, key)
  }
 }
 // observe data
 // 把data转换为响应式数据
 observe(data, true /* asRootData */)
}

const computedWatcherOptions = { lazy: true }
function initComputed (vm: Component, computed: Object) {
 // $flow-disable-line
 const watchers = vm._computedWatchers = Object.create(null)
 // computed properties are just getters during SSR
 // 判断是不是服务端渲染
 const isSSR = isServerRendering()

 for (const key in computed) {
  const userDef = computed[key]
  const getter = typeof userDef === 'function' ? userDef : userDef.get
  if (process.env.NODE_ENV !== 'production' && getter == null) {
   warn(
    `Getter is missing for computed property "${key}".`,
    vm
   )
  }
  // 如果不是ssr，则创建Watcher实例
  if (!isSSR) {
   // create internal watcher for the computed property.
   watchers[key] = new Watcher(
    vm,
    getter || noop,
    noop,
    computedWatcherOptions
   )
  }

  // component-defined computed properties are already defined on the
  // component prototype. We only need to define computed properties defined
  // at instantiation here.
  // 如果vm不存在key的同名属性
  if (!(key in vm)) {
   defineComputed(vm, key, userDef)
  } else if (process.env.NODE_ENV !== 'production') {
   if (key in vm.$data) {
    warn(`The computed property "${key}" is already defined in data.`, vm)
   } else if (vm.$options.props && key in vm.$options.props) {
    warn(`The computed property "${key}" is already defined as a prop.`, vm)
   }
  }
 }
}
sharedPropertyDefinition = {
  enumerable: true,
  cnfigurable： true,
  get: noop,
  set: noop
}
export function defineComputed (
 target: any,
 key: string,
 userDef: Object | Function
) {
 // 如果是服务端渲染，则computed不会有缓存，因为数据响应式的过程在服务器是多余的
 const shouldCache = !isServerRendering()
 // createComputedGetter返回计算属性的getter
 // createGetterInvoker返回userDef的getter
 if (typeof userDef === 'function') {
  sharedPropertyDefinition.get = shouldCache
   ? createComputedGetter(key)
   : createGetterInvoker(userDef)
  sharedPropertyDefinition.set = noop
 } else {
  // 当userDef为一个对象时
  sharedPropertyDefinition.get = userDef.get
   ? shouldCache && userDef.cache !== false
    ? createComputedGetter(key)
    : createGetterInvoker(userDef.get)
   : noop
  sharedPropertyDefinition.set = userDef.set || noop
 }
 if (process.env.NODE_ENV !== 'production' &&
   sharedPropertyDefinition.set === noop) {
  sharedPropertyDefinition.set = function () {
   warn(
    `Computed property "${key}" was assigned to but it has no setter.`,
    this
   )
  }
 }
 // 在tearget上定义一个属性， 属性名为key， 属性描述符为sharedPropertyDefinition
 Object.defineProperty(target, key, sharedPropertyDefinition)
}

function createComputedGetter (key) {
 return function computedGetter () {
  // 查找是否存在key的Watcher
  const watcher = this._computedWatchers && this._computedWatchers[key]
  if (watcher) {
   // 如果dirty为true，则重新计算，否则返回缓存
   if (watcher.dirty) {
    watcher.evaluate()
   }
   if (Dep.target) {
    watcher.depend()
   }
   return watcher.value
  }
 }
}

function createGetterInvoker(fn) {
 return function computedGetter () {
  return fn.call(this, this)
 }
}

function initWatch (vm: Component, watch: Object) {
 for (const key in watch) {
  const handler = watch[key]
  // 处理数组类型
  if (Array.isArray(handler)) {
   for (let i = 0; i < handler.length; i++) {
    createWatcher(vm, key, handler[i])
   }
  } else {
   createWatcher(vm, key, handler)
  }
 }
}

function createWatcher (
 vm: Component,
 expOrFn: string | Function,
 handler: any,
 options?: Object
) {
  // isPlainObject检查是否是对象
 if (isPlainObject(handler)) {
  options = handler
  handler = handler.handler
 }
 if (typeof handler === 'string') {
  handler = vm[handler]
 }
 // 最后调用$watch
 return vm.$watch(expOrFn, handler, options)
}

export function initProvide (vm: Component) {
 const provide = vm.$options.provide
 if (provide) {
  // 把provided存到_provided上
  vm._provided = typeof provide === 'function'
   ? provide.call(vm)
   : provide
 }
}