对象扩展

1. Object.is(v1, v2)

• 判断2个数据是否完全相等

2. Object.assign(target, source1, source2..)

• 将源对象的属性复制到目标对象上

3. 直接操作 proto 属性
   let obj2 = {};
   obj2.proto = obj1;

    console.log(0 == -0);//true
    console.log(NaN == NaN);//false
    console.log(Object.is(0, -0));//false
    console.log(Object.is(NaN, NaN));//true
        let obj3 = {};
    let obj4 = {money: 5000000};
    obj3.__proto__ = obj4;
    console.log(obj3);//{}obj3为空
    console.log(obj3.money);//5000000