It seems like it should be safe, but I can change it if you prefer.

Quote from MDN:
"In general it is best not to add, modify or remove properties from the object during iteration, other than the property currently being visited."

https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Statements/for...in
http://stackoverflow.com/questions/3463048/is-it-safe-to-delete-an-object-property-while-iterating-over-them