Is Nibbana a state of mind or an element (dhamma)?

I have four parts of this question, 1. Is Nibbana a state of mind or a dhamma? 2. If Nibbana is a state of mind, is it merely the uprooting of craving? 3. If the answer for the second question is **"Yes"**, then why it's said "Nibbana is the object of eight super-mundane consciousness? Or simply, how would a stream winner experience/see Nibbana with the existence of craving? 4. "One attain Nibbana by uprooting craving" or "One uproots craving by attaining Nibbana" Which one of the aforesaid is correct?