it seems to me that since the loading from chrome storage isn't synchronous that we'd have to do something a bit more explicit to know when the data is read and loaded in. We'd have to start out with default values for each (say null) and as they're read this would have to save the ATTR, and then loop and see if the rest are still null. If so, it carries on, and only when all of them are not null does it callback(). Just sticking callback on the last one does not guarantee it's the last one loaded.