for of和for in的区别

var array1 = [1,2,3];
array1.name = "xiaoyu";
for (var i in array1){
  console.log(i);      //依次输出1  2  3  name
}
console.log(array1.length); //输出3   这是原数组的长度


var array2 = [1,2,3];
array2.name = "xiaoyu";
for (var item of array2){
  console.log(item);     //输出1   2   3    没有输出name  
}
alert(array2.length); //输出3

var myObject={
　　a:1,
　　b:2,
　　c:3
}
for (var key in myObject) {
  console.log(key+":"+myObject[key]);//输出a:1 b:2 c:3
}