17、经典题

let obj = {
  2:3,
  3:4,
  length:2,
  push:Array.prototype.push
}
obj.push(1)            //obj[2] = 1
obj.push(2)            //obj[3] = 2
console.log(obj)



//模拟数组的push方法
Array.prototype.push = function(val){
  this[this.length] = val;            //往数组中push一个val，也就是把val放进index位数组第数组的长度位数处
    //  this.length 在原来的基础上加一，浏览器自动加一
}
//那么就得出如下结果{2: 1, 3: 2, length: 4, push: ƒ}
obj = {
  2:1,
  3:2,
  length:4,
  push:Array.prototype.push
}