Records, Values, and Structs

record.js

function Record (template) {
  if (Record.prototype.isPrototypeOf(this)) {
    var struct = this;

    Object.keys(template).forEach(function (key) {
      Object.defineProperty(struct, key, {
        enumerable: true,
        writable: true,
        value: template[key]
      });
    });
    return Object.preventExtensions(struct);
  }
  else return new Record(template);
}

struct.js

function Struct () {
  var name = arguments[0],
      keys = [].slice.call(arguments, 1),
      constructor = eval("(function "+name+"(argument) { return initialize.call(this, argument); })");

  function initialize (argument) {
    if (constructor.prototype.isPrototypeOf(this)) {
      var argument = argument,
          struct = this;

      keys.forEach(function (key) {
        Object.defineProperty(struct, key, {
          enumerable: true,
          writable: true,
          value: argument[key]
        });
      });
      return Object.preventExtensions(struct);
    }
    else return constructor.prototype.isPrototypeOf(argument);
  };

  constructor.assertIsPrototypeOf = function (argument) {
    if (!constructor.prototype.isPrototypeOf(argument)) {
      var name = constructor.name === ''
                 ? "Struct(" + keys.join(", ") + ")"
                 : constructor.name;
      throw "Type Error: " + argument + " is not a " + name;
    }
    else return argument;
  }

  return constructor;
}

value.js

var Value = (function () {

  function Value (template) {

    if (Value.prototype.isPrototypeOf(this)) {
      var immutableObject = this;

      Object.keys(template).forEach(function (key) {
        Object.defineProperty(immutableObject, key, {
          enumerable: true,
          writable: false,
          value: template[key]
        });
      });
      return Object.preventExtensions(immutableObject);
    }
    else return new Value(template);
  }

  Value.prototype = new Record({});

	function eqv (a, b) {
		var akeys, bkeys;

		if (a === b) {
			return true;
		}
		else if (a instanceof Value && b instanceof Value){
			akeys = Object.keys(a);
			bkeys = Object.keys(b);

			if (akeys.length !== bkeys.length) {
				return false;
			}
			else return akeys.every(function (key) {
				return eqv(a[key], b[key]);
			});
		}
		else return false;
	}

	Value.eqv = eqv;
	Value.prototype.eqv = function (that) {
		return eqv(this, that);
	};

	return Value;

})();

Extracted from JavaScript Spessore