js Object.keys 用法

Object.keys()   可以將對象里的所以的鍵取出來放到一個數組中

 

1、傳入對象， 返回 包含對象可枚舉屬性和方法的數組

 

var obj = {'a': 'Beijing', 'b': 'Haidian'};

 

console.log(Object.keys(obj));

    //['a', 'b']

 

2、傳入字符串，返回索引值

var str = "Beijing";

console.log(Object.keys(str));

 

// ["0", "1", "2", "3", "4", "5", "6"

3、傳入數組，返回索引值

 

var arr = ["a", "b", "c"];

 

 

console.log(Object.keys(arr));

 

//["0", "1", "2"]

 

4、構造函數，返回空數組或者屬性名

function Demo(name, age) {

this.name = name;

this.age = age;

}

console.log(Object.keys(Demo));

// []