JavaScript 'var' Hoisting

Question | Sep 20, 2015 | nextptr 

Javascript processes variable declarations before code and it moves all the declarations to top of scope. This behavior is called hoisting. Read here for more information.
It is a generally considered good practice to declare all javascript variables at top of scope. In understanding of hoisting one fact that is often overlooked is that only declarations are hoisted - not initializations.

var x = 101;
var foo = function() {
     x = 102;
     console.log(z);
};

var z = x;
foo();

What is the outcome of above code?

2015 nextptr