前言

前面我们简单的了解了 vue 初始化时的一些大概的流程，这里我们详细的了解下具体的内容;

内容

这一块主要围绕init.ts中的initState进行剖析，初始化生命周期之后紧接着。

initState

initState的方法位于scr/core/instance/state.ts中；

const sharedPropertyDefinition = {   enumerable: true,   configurable: true,   get: noop,   set: noop }  export function proxy(target: Object, sourceKey: string, key: string) {   // get方法   sharedPropertyDefinition.get = function proxyGetter() {     return this[sourceKey][key]   }   // set方法   sharedPropertyDefinition.set = function proxySetter(val) {     this[sourceKey][key] = val   }   Object.defineProperty(target, key, sharedPropertyDefinition) }  export function initState(vm: Component) {   const opts = vm.$options   // 存在props则初始化props   if (opts.props) initProps(vm, opts.props)    // Composition API   // 初始化组合式API   initSetup(vm)   // 存在方法则初始化方法   if (opts.methods) initMethods(vm, opts.methods)   // 存在data则初始化data   if (opts.data) {     initData(vm)   } else {     const ob = observe((vm._data = {}))     ob && ob.vmCount++   }   // 存在计算属性则初始化计算属性   if (opts.computed) initComputed(vm, opts.computed)   // 存在监听且监听不等于nativeWatch（这个主要是针对火狐浏览器进行处理）则初始化监听   if (opts.watch && opts.watch !== nativeWatch) {     initWatch(vm, opts.watch)   } }  function initProps(vm: Component, propsOptions: Object) {   const propsData = vm.$options.propsData || {}   const props = (vm._props = shallowReactive({}))   // cache prop keys so that future props updates can iterate using Array   // instead of dynamic object key enumeration.   // 缓存prop的keys以便将来更新props时可以使用数组代替动态的迭代对象key   const keys: string[] = (vm.$options._propKeys = [])   // 判断是否是根组件   const isRoot = !vm.$parent   // root instance props should be converted   if (!isRoot) {     // 如果不是根组件就关闭响应式处理,防止defineReactive做响应式处理     toggleObserving(false)   }   for (const key in propsOptions) {     keys.push(key)     // 对prop数据进行校验     const value = validateProp(key, propsOptions, propsData, vm)     /* istanbul ignore else */     if (__DEV__) {       const hyphenatedKey = hyphenate(key)       // 检查属性是否是保留属性       if (         isReservedAttribute(hyphenatedKey) ||         config.isReservedAttr(hyphenatedKey)       ) {         warn(           `"${hyphenatedKey}" is a reserved attribute and cannot be used as component prop.`,           vm         )       }       defineReactive(props, key, value, () => {         if (!isRoot && !isUpdatingChildComponent) {           warn(             `Avoid mutating a prop directly since the value will be ` +               `overwritten whenever the parent component re-renders. ` +               `Instead, use a data or computed property based on the prop's ` +               `value. Prop being mutated: "${key}"`,             vm           )         }       })     } else {       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.     // 在Vue.extend（）过程中，静态props已经在组件的原型上被代理。我们只需要在这里实例化时代理定义的props。     if (!(key in vm)) {       proxy(vm, `_props`, key)     }   }   // 开启响应式处理   toggleObserving(true) }  /**  * 初始化data  * @param vm  */ function initData(vm: Component) {   let data: any = vm.$options.data   // 通过getData将函数转为对象   data = vm._data = isFunction(data) ? getData(data, vm) : data || {}   if (!isPlainObject(data)) {     data = {}     // https://v2.cn.vuejs.org/v2/guide/components.html#data-%E5%BF%85%E9%A1%BB%E6%98%AF%E4%B8%80%E4%B8%AA%E5%87%BD%E6%95%B0     // 一个组件的 data 选项必须是一个函数，因此每个实例可以维护一份被返回对象的独立的拷贝     // 避免了实例之间相互影响     __DEV__ &&       warn(         'data functions should return an object:n' +           'https://v2.vuejs.org/v2/guide/components.html#data-Must-Be-a-Function',         vm       )   }   // proxy data on instance   const keys = Object.keys(data)   const props = vm.$options.props   const methods = vm.$options.methods   let i = keys.length   while (i--) {     const key = keys[i]     // 检查key名是否在methods中已经使用     if (__DEV__) {       if (methods && hasOwn(methods, key)) {         warn(`Method "${key}" has already been defined as a data property.`, vm)       }     }     // 检查key名是否在props中使用     if (props && hasOwn(props, key)) {       __DEV__ &&         warn(           `The data property "${key}" is already declared as a prop. ` +             `Use prop default value instead.`,           vm         )       // 检查key名是否符合规范,即不以$和_开头     } else if (!isReserved(key)) {       // 代理数据 |本质上还是 Object.defineProperty       proxy(vm, `_data`, key)     }   }   // observe data | 响应式数据   const ob = observe(data)   ob && ob.vmCount++ } /**  * 获取data内容|转为对象  * @param data  * @param vm  * @returns  */ export function getData(data: Function, vm: Component): any {   // #7573 disable dep collection when invoking data getters   pushTarget()   try {     return data.call(vm, vm)   } catch (e: any) {     handleError(e, vm, `data()`)     return {}   } finally {     popTarget()   } }  const computedWatcherOptions = { lazy: true }  function initComputed(vm: Component, computed: Object) {   // $flow-disable-line   // 创建一个空对象   const watchers = (vm._computedWatchers = Object.create(null))   // computed properties are just getters during SSR   // 计算的内容只是SSR期间的getter   // 是否服务端渲染   const isSSR = isServerRendering()    for (const key in computed) {     const userDef = computed[key]     const getter = isFunction(userDef) ? userDef : userDef.get     if (__DEV__ && getter == null) {       warn(`Getter is missing for computed property "${key}".`, vm)     }      if (!isSSR) {       // create internal watcher for the computed property.       // 不是服务端渲染,就为计算属性创建内部观察程序。       // noop 空函数：function() {}       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.     // 组件定义的计算内容已经在组件原型上定义。我们只需要在这里定义实例化时定义的计算内容。     if (!(key in vm)) {       defineComputed(vm, key, userDef)     } else if (__DEV__) {       // 开发环境下检查key名是否被过早的定义在data,props,methods中       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 "${key}" is already defined as a prop.`, vm)       } else if (vm.$options.methods && key in vm.$options.methods) {         warn(           `The computed property "${key}" is already defined as a method.`,           vm         )       }     }   } }  export function defineComputed(   target: any,   key: string,   userDef: Record<string, any> | (() => any) ) {   // 是否服务端渲染   const shouldCache = !isServerRendering()   // 定义get和set   if (isFunction(userDef)) {     sharedPropertyDefinition.get = shouldCache       ? createComputedGetter(key)       : createGetterInvoker(userDef)     sharedPropertyDefinition.set = noop   } else {     sharedPropertyDefinition.get = userDef.get       ? shouldCache && userDef.cache !== false         ? createComputedGetter(key)         : createGetterInvoker(userDef.get)       : noop     sharedPropertyDefinition.set = userDef.set || noop   }   if (__DEV__ && sharedPropertyDefinition.set === noop) {     sharedPropertyDefinition.set = function () {       warn(         `Computed property "${key}" was assigned to but it has no setter.`,         this       )     }   }   Object.defineProperty(target, key, sharedPropertyDefinition) }  function createComputedGetter(key) {   return function computedGetter() {     const watcher = this._computedWatchers && this._computedWatchers[key]     if (watcher) {       // 是否被计算过,如果dirty为true表明未被计算过       if (watcher.dirty) {         watcher.evaluate() // 调用watcher.get方法,值会保存在watcher.value上       }       if (Dep.target) {         if (__DEV__ && Dep.target.onTrack) {           Dep.target.onTrack({             effect: Dep.target,             target: this,             type: TrackOpTypes.GET,             key           })         }         watcher.depend()       }       return watcher.value     }   } }  function createGetterInvoker(fn) {   return function computedGetter() {     return fn.call(this, this)   } }  function initMethods(vm: Component, methods: Object) {   const props = vm.$options.props   // 循环遍历methods   for (const key in methods) {     if (__DEV__) {       // 不是函数类型发出警告       if (typeof methods[key] !== 'function') {         warn(           `Method "${key}" has type "${typeof methods[             key           ]}" in the component definition. ` +             `Did you reference the function correctly?`,           vm         )       }       // 函数名称和props中的是否冲突       if (props && hasOwn(props, key)) {         warn(`Method "${key}" has already been defined as a prop.`, vm)       }       // 函数名不能以_和$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 $.`         )       }     }     // 将methods绑定在当前实例上     vm[key] = typeof methods[key] !== 'function' ? noop : bind(methods[key], vm)   } }  function initWatch(vm: Component, watch: Object) {   // 遍历watch   for (const key in watch) {     const handler = watch[key]     // 是否是数组     if (isArray(handler)) {       // 循环创建watcher监听回调函数       for (let i = 0; i < handler.length; i++) {         createWatcher(vm, key, handler[i])       }     } else {       // 创建watcher监听回调函数       createWatcher(vm, key, handler)     }   } }  function createWatcher(   vm: Component,   expOrFn: string | (() => any),   handler: any,   options?: Object ) {   // 检查是否是普通对象   if (isPlainObject(handler)) {     // 将handler挂载到options属性上     options = handler     // 提取handler属性赋值给handler     handler = handler.handler   }   // 是否是字符串   if (typeof handler === 'string') {     // 从实例中找到handler赋值给handler     handler = vm[handler]   }   // 实例上的$watch方法   return vm.$watch(expOrFn, handler, options) }