var a = function() {
      var z = "a";
      window.b = function() { z = "b"; }
      window.c = function() { return z; }
    };
    a();
    window.c(); // returns "a"
    window.b();
    window.c(); // returns "b"

So each function does not have its own closure -- closures work "upwards", referencing everything in every scope above them.