gistfile1.js

var A = function(){
  console.debug("A constructor");
  A.build();
}; 
(function(){
  var p = 0;
 
  this.B = function(){
      console.debug('B constructor');
  };
  this.B.prototype = {
    foo: function(){console.debug("p:",p); return p;}
  };

  var self = this;
  this.build = function() {
    console.debug('build function');
    return new self.B();
  }

}).apply(A);

var a = A.build();
var aa = new A();
var b = new A.B();
console.debug([a,aa,b, b.foo() ])