Vue.observable

Vue.observable 可以代替 VueX 作为小型全局状态托管工具。看看用法：

import Vue from 'vue'

// 模拟 state
const state = Vue.observable({
  name: 'John Doe',
  email: 'fake@email.com',
  username: 'jd123',
  posts: ['post 1', 'post 2', 'post 3', 'post 4'],
})

// 模拟 getter
export const getters = {
  postsCount: () => state.posts.length,
}

// 模拟 mutation
export const mutations = {
  insertPost: (post) => state.posts.push(post),
}

组件内引入的方法和 VueX 是一样的，mapState 和 mapMutation 可以自己实现。

Vue.observable 源码：

// src\core\observer\index.js

function observe(value: any, asRootData: ?boolean): Observer | void {
  if (!isObject(value) || value instanceof VNode) {
    return
  }
  let ob: Observer | void
  // 判断是否存在__ob__响应式属性
  if (hasOwn(value, '__ob__') && value.__ob__ instanceof Observer) {
    ob = value.__ob__
  } else if (
    shouldObserve &&
    !isServerRendering() &&
    (Array.isArray(value) || isPlainObject(value)) &&
    Object.isExtensible(value) &&
    !value._isVue
  ) {
    // 实例化Observer响应式对象
    ob = new Observer(value)
  }
  if (asRootData && ob) {
    ob.vmCount++
  }
  return ob
}

class Observer {
  value: any
  dep: Dep
  vmCount: number // number of vms that have this object as root $data
  constructor(value: any) {
    this.value = value
    this.dep = new Dep()
    this.vmCount = 0
    def(value, '__ob__', this)
    if (Array.isArray(value)) {
      if (hasProto) {
        protoAugment(value, arrayMethods)
      } else {
        copyAugment(value, arrayMethods, arrayKeys)
      }
      this.observeArray(value)
    } else {
      // 实例化对象是一个对象，进入walk方法
      this.walk(value)
    }
  }
  walk(obj: Object) {
    const keys = Object.keys(obj)
    // 遍历key，通过defineReactive创建响应式对象
    for (let i = 0; i < keys.length; i++) {
      defineReactive(obj, keys[i])
    }
  }
}

function defineReactive(obj: Object, key: string, val: any, customSetter?: ?Function, shallow?: boolean) {
  const dep = new Dep()

  const property = Object.getOwnPropertyDescriptor(obj, key)
  if (property && property.configurable === false) {
    return
  }

  // cater for pre-defined getter/setters
  const getter = property && property.get
  const setter = property && property.set
  if ((!getter || setter) && arguments.length === 2) {
    val = obj[key]
  }

  let childOb = !shallow && observe(val)
  // 接下来调用Object.defineProperty()给对象定义响应式属性
  Object.defineProperty(obj, key, {
    enumerable: true,
    configurable: true,
    get: function reactiveGetter() {
      const value = getter ? getter.call(obj) : val
      if (Dep.target) {
        dep.depend()
        if (childOb) {
          childOb.dep.depend()
          if (Array.isArray(value)) {
            dependArray(value)
          }
        }
      }
      return value
    },
    set: function reactiveSetter(newVal) {
      const value = getter ? getter.call(obj) : val
      /* eslint-disable no-self-compare */
      if (newVal === value || (newVal !== newVal && value !== value)) {
        return
      }
      /* eslint-enable no-self-compare */
      if (process.env.NODE_ENV !== 'production' && customSetter) {
        customSetter()
      }
      // #7981: for accessor properties without setter
      if (getter && !setter) return
      if (setter) {
        setter.call(obj, newVal)
      } else {
        val = newVal
      }
      childOb = !shallow && observe(newVal)
      // 对观察者watchers进行通知,state就成了全局响应式对象
      dep.notify()
    },
  })
}