Object.keys方法之详解

• 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"]
  
  var obj2 = Object.create({}, { getFoo : { value : function () { return this.foo } } });
  obj2.foo = 1;
  console.log(Object.keys(obj2)); // console: ["foo"]
  

• 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"]