[Javascript] for in / for of

1) for in

var obj = {
    x : 1,
    y : 2,
    z : 3
};

for (var i in obj) {
    console.log(i + " : " + obj[i]);
}

=>

x : 1
y : 2
z : 3

 

2) for of

var array = [1, 2, 3];

for (var val of array) {
  console.log(val);
}

=>

1, 2, 3