JavaScript 'var' Hoisting

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?