Object.keys()返回对象的属性

 <script>
         // 传入对象，返回属性名
         let obj = {
             'a': '123',
             'b': '456'
         }
         console.log(Object.keys(obj)) //["a","b"]
         // 传入字符串，返回索引
         let str = 'abc'
         console.log(Object.keys(str)) //["0","1","2"]
         // 构造函数，返回空数组或属性名
         function Person(name, age, gender) {
             this.name = name;
             this.age = age;
             this.gender = gender;
             this.toString = function () {
                     return (this.name + ", " + this.age + ", " + this.gender);
             }
         }
             console.log(Object.keys(Person)) // []
         // 数组返回索引
         let arr = ["a", "b", "c"]
         console.log(Object.keys(arr)) // ["0", "1", "2"]
 </script>