看vue源码，梳理一下响应式对象
输入

 const obj = {
  a: {
    num: 1,
    text: '123'
  },
  b: {
    num: 2
  },
};

输出

obj={
  a: {
    num: 1,
    text: "123",
    __ob__: Observer {value: {…}, dep: Dep},
    get num: ƒ reactiveGetter(),
    set num: ƒ reactivesetter(newVal),
    get text: ƒ reactiveGetter(),
    set text: ƒ reactivesetter(newVal),
    __proto__: Object,
  },
  b:{
    num: 2,
    __ob__: Observer {value: {…}, dep: Dep},
    get num: ƒ reactiveGetter(),
    set num: ƒ reactivesetter(newVal),
    __proto__: 
  },
  __ob__: Observer {value: {…}, dep: Dep},
  get a: ƒ reactiveGetter(),
  set a: ƒ reactivesetter(newVal),
  get b: ƒ reactiveGetter(),
  set b: ƒ reactivesetter(newVal),
  __proto__: Object,
}

实现

let uid = 0;
//保存订阅者
class Dep {
  constructor(){
    this.id = uid++;
    this.subs = [];
  }

  addSub(sub) {
    this.subs.push(sub);
  }

//发布通知
  notify() {
    let subs = this.subs.slice();
    for (let i = 0; i < subs.length; i++) {
      subs[i].update();
    }
  }
}

//给对象挂载__ob__: {value...,dep...}
function def(obj, key, val,enumerable) {
  Object.defineProperty(obj, key, {
    value: val,
    enumerable: !!enumerable,
    writable: true,
    configurable: true
  });
}

//给对象挂载get set
function defineReactive(obj, key, val) {
  const dep = new Dep();
  let property = Object.getOwnPropertyDescriptor(obj, key);
  if (property && property.configurable === false) {
    return;
  }
  const getter = property && property.get;
  const setter = property && property.set;

  if ((!getter || setter)) {
    val = obj[key];
  }
  let childOb = observer(val);
  Object.defineProperty(obj,key,{
    enumerable: true,
    configurable: true,
    get:function reactiveGetter() {
      const value = getter ? getter.call(obj) : val;
      return value;
    },
    set: function reactivesetter(newVal) {
      const value = getter ? getter.call(obj) : val;
      if (newVal === value) {
        return
      }
      if (getter && !setter) return
      if (setter) {
        setter.call(obj, newVal)
      } else {
        val = newVal
      }
      childOb = observer(newVal);
    //触发通知
      obj.__ob__.dep.notify();
    }
  })
}

//深度遍历对象里的值 把每个都变成响应式
class Observer{
  constructor(value) {
    console.info(this);
    this.value = value;
    this.dep = new Dep();
    def(value, '__ob__', this);
    if (Array.isArray(value)) {

    }else {
      this.walk(value);
    }
  }

  walk(obj){
    const keys = Object.keys(obj);
    for (let i = 0; i < keys.length; i++) {
      defineReactive(obj, keys[i]);
    }
  }
}

//把普通对象变成响应式对象
function observer(value) {
  if (typeof value !== 'object') {
    return;
  }
  let ob;
  ob = new Observer(value);
  return ob;
}

const obj = {
  a: {
    num: 1,
    text: '123'
  },
  b: {
    num: 2
  },
};

let up = {
  update: () => {
    console.log('update...');
  }
};
observer(obj);
console.info(obj);
obj.__ob__.dep.addSub(up);

obj.a = 10;