My computer does not even support MIDI. I have to use an external driver called Timidity:
You can package Timidity with your project if you follow the license. You can also use Timidity to convert midi files into WAV, or OGG files. This would only be useful for the NodeWebkit, and you would need to pass commands via CLI.
I hope if Chrome adds Midi they also include some sort of MIDI driver for crappy computers like mine.