old_contents: angular.module('app.services')
  
  .service('BillService', [function(){
    var bill = {
      vat: 0,
      serviceCharge: 0
    };
  
    return {
  
      setBill: function(bill) {
        bill = bill;
      },
      
      getBill: function() {
        return bill;
      }
  
    };
  }]);
new_contents: angular.module('app.services')
  
  .service('BillService', [function(){
    var bill = {
      totalAmount: undefined,
      vat: 0,
      serviceCharge: 0
    };
  
    return {
  
      setBill: function(bill) {
        bill = bill;
      },
      
      getBill: function() {
        return bill;
      }
  
    };
  }]);
subject: Refactor bill service