Related, GBA.js is a project a friend of mine has been working on to make a GameBoy Advance emulator in pure Javascript. A WIP version is running at http://endrift.com/gbajs/index.html but there's a lot of bugs and compatibility is far from perfect. Source code is all on GitHub at https://github.com/jpfau/gbajs/
ahahahaha, I'm working on my own GBA emulator in JS too. It seems I might have started a trend, since I've been working on https://github.com/grantgalitz/IodineGBA for a bit now.