The GitHub page in question has now been taken down in line with the request made by Nintendo.
The company has decided to take down all the related content from GitHub and even wrote to them officially with a list of titles that the website is being used to get unauthorized access to:
Nintendo requests that GitHub, Inc., disable public access to the web site at http://jsemu.github.io/gba/. This web site provides access to unauthorized copies of Nintendo’s copyright-protected video games and videos making use of Nintendo’s copyrighted Pokémon characters and imagery in violation of Nintendo’s exclusive rights.
The list of games that the browser based Game Boy emulator was being used to play includes Advance Wars, Advance Wars 2: Black Hole Rising, Fire Emblem, F-Zero: GP Legend, F-Zero: Maximum Velocity, Game & Watch Gallery 4, Golden Sun, Kirby & The Amazing Mirror, Kirby: Nightmare in Dream Land, Mario & Luigi: Superstar Saga, Mario Kart – Super Circuit, Mario Party Advance, Mario Pinball Land: Super Mario Ball.
There also are numerous games from Pokemon, Metroid, Super Mario Advance and Legend of Zelda franchises.
There is a niche in the gaming industry where playing old classics using browser based emulators is a norm and I can see a lot of dedicated gamers not liking this decision.
Services like these provide a massive dose of nostalgia to the old timers but sadly Nintendo doesn’t want unofficial projects like these to get promoted. The browser based Game Boy emulator taken down by Nintendo is one of the few services of its kind, will you be affected?