Javascript Scoping Confusion

Question

I could not find an exact match on my issue, although many questions on the javascript scope really exist. Here is my current code for the question.

var my_var = "blank";
var MyFunc = function() {
    my_var = "one";
    //var my_var = "two";
}
alert(my_var);
MyFunc();
alert(my_var);

When I run this, I am warned with "empty" and then "one" as expected. However, if I uncomment this line, it looks like this.

var my_var = "blank";
var MyFunc = function() {
    my_var = "one";
    var my_var = "two";
}
alert(my_var);
MyFunc();
alert(my_var);

I am warned with "blank" and then "blank" . This is not what I would expect, and I am confused that adding a line will remove the behavior. Can someone explain what is going on here? I see this behavior in both firefox and safari.

Answer 1

var "" ( ). , , var my_var , , "my_var" .

( " ", var , , .)

Answer 2

, JavaScript. .

Answer 3

Javascript , C, ++, Java #, ( ).

: JavaScript

http://net.tutsplus.com/tutorials/javascript-ajax/quick-tip-javascript-hoisting-explained/