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>