var oEspressoWithMochaAndWhip = new Espresso(); oEspressoWithMochaAndWhip = new Mocha(oEspressoWithMochaAndWhip); oEspressoWithMochaAndWhip = new Whip(oEspressoWithMochaAndWhip); console.log(oEspressoWithMochaAndWhip.cost());