Object.keys

Object.keys()返回对象可枚举属性构成的字符串数组，数组的排列顺序与for--in循环一致

1.Array

Object.keys([1, 2, 3]) //[0,1,2] 可枚举属性为其序号

2.Object

Object.keys({a: 1, b: 2}) //[a,b]

注意:其顺序与for--in循环一致

let a = { 100: 'a', 2: 'b', 7: 'c' };;
console.log(Object.keys(a)) //[2, 7, 100]
for( var i in a){
console.log(i)
}

//2 7 100

详情可查看: https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/keys