(function() {
  var Calculator = {
    add: function(a, b) { return a + b; },
    subtract: function(a, b) { return a - b; },
    multiply: function(a, b) { return a * b; },
    divide: function(a, b) {
      return b !== 0 ? a / b : 'Error';
    }
  };
  console.log(Calculator.add(10, 5));
})();