Object.keys详解

实际开发中，有时候需要知道对象的所有属性，原生js提供了一个很好的方法：

Object.keys()，该方法返回一个数组

传入对象，返回属性名

var obj = {
        'a':'123',
        'b':'345'
};
console.log(Object.keys(obj));  //['a','b']
var obj1 = { 
        100: "a", 
        2: "b", 
        7: "c"
};
console.log(Object.keys(obj1)); // console: ["2", "7", "100"]

传入字符串，返回索引

var str = 'ab1234';
console.log(Object.keys(obj));  //[0,1,2,3,4,5]

构造函数 返回空数组或者属性名

function Pasta(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(Pasta)); //console: []

    var spaghetti = new Pasta("Tom", 20, "male");
    console.log(Object.keys(spaghetti)); //console: ["name", "age", "gender", "toString"]

数组 返回索引

    var arr = ["a", "b", "c"];
    console.log(Object.keys(arr)); // console: ["0", "1", "2"]