When i copy the code in a folder names npcscan it doesn't appear in the list of loaded addons.
If i rename the folder to unitscan it appears but it doesn't work - doesn't select the npc although i'm right by it and i use /unit scan npc_name

Only the retail branch is supposed to work in classic and only with a lot of limitations due to the API changes. Also, the command is /unitscan without spaces.