Vue.extend源码解读

Vue.extend源码解读

//源码位置:src/core/global-api/extend.js
import { ASSET_TYPES } from 'shared/constants'
import { defineComputed, proxy } from '../instance/state'
import { extend, mergeOptions, validateComponentName } from '../util/index'
/*
思路：Sub继承Super.prototype原型链上的属性或者方法,将Super构造函数的静态属性赋值给Sub
  Sub.superOptions = Super.options(子类存储父类的Options)
  Sub.extendOptions = extendOptions(子类存储自身原有的Options)
  Sub.sealedOptions = extend({}, Sub.options)(子类存储合并后的Options)

结果:创建子类
*/
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: Object): Function {
    extendOptions = extendOptions || {}
    const Super = this
    const SuperId = Super.cid
    const cachedCtors = extendOptions._Ctor || (extendOptions._Ctor = {})
    if (cachedCtors[SuperId]) {
      return cachedCtors[SuperId]
    }

    const name = extendOptions.name || Super.options.name
    if (process.env.NODE_ENV !== 'production' && name) {
      validateComponentName(name)
    }

    const Sub = function VueComponent (options) {
      this._init(options)
    }
    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
    //代理Sub.options.props
    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
  }
}
function initProps (Comp) {
  const props = Comp.options.props
  for (const key in props) {
    proxy(Comp.prototype, `_props`, key)
  }
}

function initComputed (Comp) {
  const computed = Comp.options.computed
  for (const key in computed) {
    defineComputed(Comp.prototype, key, computed[key])
  }
}

initProps执行过程

/*
 过程:子类的options.props便利，通过proxy方法将options.props中的key通过 Object.defineProperty方法代理到类的原型prototype上，重写key的get和set方法，当对key进行操作的同时其实是对vm._props.key进行操作
 结果:this.key = this._props.key
*/
function initProps (Comp) {
 const props = Comp.options.props
 for (const key in props) {
   proxy(Comp.prototype, `_props`, key)
 }
} 
function proxy (target: Object, sourceKey: string, key: string) {
 sharedPropertyDefinition.get = function proxyGetter () {
   return this[sourceKey][key]
 }
 sharedPropertyDefinition.set = function proxySetter (val) {
   this[sourceKey][key] = val
 }
 Object.defineProperty(target, key, sharedPropertyDefinition)
}