remove filter and map methods. It is unclear what they should return. Should it return a set? What if the set has been subclassed then should the returned value be an instance of that subclass? Should they simply return an array? The ECMAScript committee has not included filter and map in any draft of Set. I dont want to end up with Object Set being inconsistent with the final spec. Folks using ObjectSet will need to make do with forEach.
change the empty method to be called clear to match the ECMAScript draft for Set. Spec chasing is not fun.
change length to size to match the ECMAScript spec
remove isEmpty method. There is nothing like it in the ECMAScript spec and users of ObjectSet can use set.size === 0.
do not send the set as the second argument to the callback function when iterating. The ECMAScript committee has this crazy idea that the set should be sent as the third argument. By making this change here, we'll be able to match the ECMAScript spec when it is finalized.