We have code like: 

var numbers = [1,2,3];for(var i in numbers){     setTimeout(function(){console.log(numbers[i]);     }, 0);}//3//3//3

Note:

1. function block doesn‘t create scope!

2. setTimeout function run after all the other code finished.

Therefore, before setTimeout get run, for block already exec 3 times and i was set to 2. 

Once setTimeout get running, it prints out numbers[i] which is 3.

Now, we change the code to:

var numbers = [1,2,3];for(var i  in  numbers){   (function(){       var j = i;        setTimeout(function(){           console.log(numbers[j]);        })    })();}//1//2//3

Note:

1. function does create new scope.

2. the (function(){})() run immedatly.

3. (function(){}) inside for block actually is closure which does remeber the local var value (in our case is var j).

[Javascript] Function scope