Vue面试中observable原理详解

Vue.observable({ count : 1})

new vue({ count : 1})

// 引入vue
import Vue from 'vue
// 创建state对象，使用observable让state对象可响应
export let state = Vue.observable({
  name: '张三',
  'age': 38
})
// 创建对应的方法
export let mutations = {
  changeName(name) {
    state.name = name
  },
  setAge(age) {
    state.age = age
  }
}

<template>
  <div>
    姓名：{{ name }}
    年龄：{{ age }}
    <button @click="changeName('李四')">改变姓名</button>
    <button @click="setAge(18)">改变年龄</button>
  </div>
</template>
import { state, mutations } from '@/store
export default {
  // 在计算属性中拿到值
  computed: {
    name() {
      return state.name
    },
    age() {
      return state.age
    }
  },
  // 调用mutations里面的方法，更新数据
  methods: {
    changeName: mutations.changeName,
    setAge: mutations.setAge
  }
}

export 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
}

export 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])
    }
}

export 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()
    }
  })
}