[mike-cardwell]

> `var` declares the variable globally"

Not quite. var's are hoisted to the top of their most local function.

  (function(){
    (function(){
      var x = 123;
    })();
    {
      var y = 123;
    }
    // Here, x is not defined, but y is
  })();
  // Here, neither x nor y are defined

The above code essentially gets translated to the following:

  (function(){
    var y;
    (function(){
      var x;
      x = 123;
    })();
    {
      y = 123;
    }
    // Here, x is not defined, but y is
  })();
  // Here, neither x nor y are defined