18.104.22.168.3 Enumerator.prototype.item ( )
If the this object is not an Enumerator object, raise a TypeError exception.
Let collection be the value of the this object’s [[Collection]] property.
If collection is undefined, return undefined.
Let state be the value of the this object’s [[EnumerationState]] property.
If state indicates that the end of the enumeration has been reached, return undefined.
Return the current enumeration item as indicated by state.