let obj = { 1: { id: 1, a: 2, b: 3 }, 2: { id: 1, a: 2, b: 3 } };
const {
  1: {},
  ...afterDel
} = obj;
console.log(afterDel);

let obj = { a: {}, b: { a: 2 } };
let { a, ...aa } = obj;
console.log(aa);

for (const key in filter) {
  if (filter[key] === "") {
    delete filter[key];
  }
}

let user = {
  name: "wang",
  age: 20,
};
let key = "name";
user[key]; //=>  输出wang

//key 可以是一个变量
let key = prompt("What do you want to know about the user?", "name");
//prompt  浏览器的输入弹窗  在输入后会返回输入的值给key（默认输入name）
user[key]; //==> John（如果输入 "name"）

let key = prompt("What do you want to know about the user?", "name");

let user = {
  [key]: "wang", // 属性名是从 key 变量中得到的
};

alert(user.name); // 5 如果 key="name"

user.key === undefined  返回true表示不存在
“key” in user  返回true表示存在

let obj = { a: "", b: 2, c: "wang" };
let target = {};
Object.keys(obj).map((v) => (obj[v] !== "" ? (target[v] = obj[v]) : ""));
console.log(target); //=>{b: 2, c: "wang"}

let o = {};
let p = Object.create(null);
Object.prototype.say = function(){
    console.log('hello')
}
console.log(o.say)
console.log(p.say)

>> f(){}
>> undefined

let val = { 1: { a: 1, b: 3 }, 2: { a: 2, b: 5 } };
let newVal = { ...val["1"], b: 4 };
val = { ...val, 1: newVal };
//outinput {"1":{a:1,b:4},"2":{a:2,b:5}}

class A {
  constructor() {
    this.nameA = "a";
  }
  wangA() {
    console.log("A");
  }
}

class B extends A {
  constructor() {
    super();
    this.nameB = "b";
  }
  wangB() {
    console.log("B");
  }
}

class C extends B {
  constructor() {
    super();
    this.nameC = "c";
  }
  wangC() {
    console.log("C");
  }
}

var c = new C();
let arr = [];
function FindMembers(L, att, method) {
  if (L.__proto__) {
    let Att = Object.keys(L).filter((a) => a.indexOf(att) > -1);
    let Method = Object.getOwnPropertyNames(L.__proto__).filter(
      (m) => m.indexOf(method) > -1
    );
    arr = arr.concat(Att, Method);
    FindMembers(L.__proto__, att, method);
  }
  return arr;
}
const members = FindMembers(c, "name", "wang");
console.log("members", members);