In Flaam, Stavanger amd Oslo we used euros with no problem whatsoever....in fact never bought any of the local currency!!
Norway has even less involvement with the EU than we in the UK do so, just like us, the euro is a foreign currency (and have you thought what it would be like if you tried to spend euro in Liverpool?). Credit cards are widely accepted but otherwise I recommend you take krone as it's pretty essential for odd purchases such as coffee or local transport. If you do try to spend euro the rate of exchange would be very poor.