This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.
Object. It is returned or used as an argument by
Node.getUserData(), used as the third argument to
UserDataHandler, and is used or returned by various
DOMUserData is not persisted nor serialized and will not be present after the application has restarted or after a crash. If you are interested in persisting data you might rather need to use