Nonetheless, implementing MIDI through javascript would be kind of cool. I'm about 90% done an HTML5 emulation of a Boss DR-110 (warts and all), and while the timing of the audio playback ain't great, I'd be curious to see if better results could be achieved by sending the sequencer data out as MIDI instead.
Considering how picky folks get about latency in audio software though, generating MIDI with Javascript seems more useful as a learning tool than an actual music production tool.