How to know if there are any deleted keys in Knouckout’s observableKeySet?

self.Items = new keySet.ObservableKeySet();
self.Items.addAll();
Now if any key is deleted from Items, how can I know that?

self.misc = function() {
            if(self.selectedItems().isAddAll()){
                if(self.selectedItems().keys.seletedKeys.size>0)
                    return true;
            } else {
                return false;
            }
};

Cannot read properties of undefined (reading ‘size’) in expression
I’m getting this error from above function. How to solve this?