javascript - Why is x undefined in inner scope?

In the code below

var x = 1;

(function () {

  console.log(x);
  var x = 2;
}());

Why is it that when console.log(x), x is undefined?

Answer

Variable hoisting. The actual code is executed like this.

var x = 1;

(function() {
    var x; // x = undefined
    console.log(x);
    x = 2;
})();

Edit: On Mr Lister's advice, a bit on variable hoisting. From MDN (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/var):

"Variable declarations, wherever they occur, are processed before any code is executed. The scope of a variable declared with var is its current execution context, which is either the enclosing function or, for variables declared outside any function, global."