test-types.js

// with defined properties
function accessors(index) {
  return {
    enumerable: true, configurable: false,
    get: function() { return this._value[index]; },
    set: function(value) { this._value[index] = value; }
  };
}

function defineTypeWithDefinedProperties(fields) {
  function Type(values) { this._value = values || []; }
  var _len = fields.length, properties = {};
  for (var i = 0; i < _len; ++i) properties[fields[i].name] = accessors(i);
  Type.prototype = Object.create(Object.prototype, properties);
  return Type;
}

// with get/set on prototype
function defineTypeWithGetSetOnPrototype(fields) {
  function Type(values) { this._value = values || []; }
  var _len = fields.length, properties = {};
  for (var i = 0; i < _len; ++i) properties[fields[i].name] = i;
  Type.prototype.properties = properties;
  Type.prototype.get = function(prop) {
    return this._value[Type.prototype.properties[prop]];
  };

  Type.prototype.set = function(prop, value) {
    this._value[Type.prototype.properties[prop]] = value;
  };

  return Type;
}

// prep
var fields = [ { name: 'first' }, { name: 'second' } ];
var WithDefinedProperties = defineTypeWithDefinedProperties(fields);
var WithGetSetOnPrototype = defineTypeWithGetSetOnPrototype(fields);

var definedWithValues = new WithDefinedProperties([1, "two"]);
var definedWithNoValues = new WithDefinedProperties();

var getSetWithValues = new WithGetSetOnPrototype([1, "two"]);
var getSetWithNoValues = new WithGetSetOnPrototype();