Object.keys()

Object.keys（obj），返回一个数组，数组里是该obj可被枚举的所有属性名。请看示例：

示例一：

function Pasta(grain, width, shape) {
    this.grain = grain;
    this.width = width;
    this.shape = shape;
    this.toString = function () {
        return (this.grain + ", " + this.width + ", " + this.shape);
    }
}

console.log(Object.keys(Pasta)); //console: []
var spaghetti = new Pasta("wheat", 0.2, "circle");
console.log(Object.keys(spaghetti)); //console: ["grain", "width", "shape", "toString"]

示例二：

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

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

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