Its possible to add an embedded emulator on the page and play levels online?
The closest we've gotten to having an emulator inside the browser is the RetroArch Web Player, which runs at a barely tolerable speed and I'm not sure if it can be embedded. You'd also need to make the user provide their own clean ROM, download the patch from the server, and apply it locally. Overall, I'd say it'd be way too much work for something which wouldn't even be properly playable.
After a bit of searching I found this, which seems to run at an acceptable framerate, but it seems pretty complicated to get running and as telinc said you'd need to provide your own clean ROM, which would be a hassle for both me and the user.
Ehm i test one of the lvls but i get error this patch is not for this rom i get Super Mario World (U) [!] from the goddsnes folder wich is the right super mario world rom.Wich rom i need to test some of the lvls