How to get previous node in onMoveNode

Hi. Thanks a lot for this library. It looks really promising for my project. However I have one question. I'm using https://github.com/collectiveidea/awesome_nested_set in rails backend and to move node it accepts only move_to_left_of node and move_to_right_of_node. The problem is now to find the previous node in onMoveNode callback. How to get previous node here? Let's say I want to move node B into C before D.

- A
- B
- C
- D