You can use ivars so you don't need to make so many hilarious classes

classWithIvar.cocoascript.js

// Make a class with some handlers. 
function Class(handlers){
  var uniqueClassName = "fetchDelegate_" + NSUUID.UUID().UUIDString();
  var cls = MOClassDescription.allocateDescriptionForClassWithName_superclass_(uniqueClassName, NSObject);
  // Add each handler to the class description
  for(var selectorString in handlers) {
    var sel = NSSelectorFromString(selectorString);
    cls.addInstanceMethodWithSelector_function_(sel, handlers[selectorString]);
  }
  // Add ivar to store instance-specific info
  const ok = cls.addInstanceVariableWithName_typeEncoding("extraInfo", "@");
  return cls.registerClass();
};


const cls = Class({
  // Use this new syntax, but not arrow syntax to make sure we can still access the instance as this
  "test"() {
    log("extra = " + this.valueForKey("extraInfo"))
  },
});

const instance = cls.new();

// Slightly inelegant, can use properties to make it a bit shorter
instance.setValue_forKey({a:123}, "extraInfo");

instance.test();
/* Output
extra = {
    a = 123;
}
*/