Variable declarations in JS

gistfile1.js

var a = 0;
(function() {
  var f = function() {
    console.log(a);
  };
  f();
})(); // 0

var b = 0;
(function() {
  var f = function() {
    console.log(b);
  };
  f();
  var b = 5;
  f();
})(); // undefined, 5