Sum function with carring

sum.js

function sum(n) {
  var self = sum;
  
  if (typeof n === 'undefined') {
    var result = self.numbers.reduce(function (prev, next) { return prev + next; }, 0);
    self.numbers = [];
    return result;
  }
  
  if ( ! self.numbers ) { self.numbers = [] };
  self.numbers.push(n);
  return self;
}

var sum = (function () {
  var numbers = [];
  
  return function sum(n) {
    if (typeof n === 'undefined') {
      var result = numbers.reduce(function(prev, next) { return prev + next; });
      numbers = [];
      return result;
    }
    
    numbers.push(n);
    return sum;
  };
})();

var sum = (function () {
  var numbers = [];
  
  return function (n) {
    if (typeof n === 'undefined') {
      var result = numbers.reduce(function(prev, next) { return prev + next; });
      numbers = [];
      return result;
    }
    
    numbers.push(n);
    return arguments.callee;
  };
})();