Object.keys()的簡單理解

1、物件的話返回屬性名

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"]

2、陣列的話返回索引

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

3、字串的話返回索引

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