Anyone tried this or know if it's possible? Missus wants a NES Classic but we don't have a TV (we're odd like that!). She has a 2015 15inch MPB, and I've got a late 2012 iMac. Can it be done on either? Or have i Got to get a TV too?
The issue is that the computers aren't displays. They are computers. It's possible, but it isn't really what you are looking for. There's no good way to turn these computers into displays, even if they have one. It's a hardware limitation.
Now, you could get video capture hardware, but it's easier just using OpenEMU like the other poster says, or buying a cheap 1080p monitor. And depending on how good the video capture tool is, it can be in the same price range (or more) than even a gaming 1080p monitor, but introduce lag because it's capturing and processing the video rather than displaying it. That's why I don't recommend it.