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"]

    var arr = ["a", "b", "c"];

    console.log(Object.keys(arr)); // console: ["0", "1", "2"]

var str = 'ab1234';

console.log(Object.keys(obj));  //[0,1,2,3,4,5]