Visit on Github.
http://webaudio.github.io/web-midi-api/
(TR version has wrong Editors Draft link; I had to track it down on GitHub. http://www.w3.org/TR/webmidi/).
I have independently left some feedback on their repo before (issues here).
The attempts at making a Map-like class seem to have gone horribly awry: http://webaudio.github.io/web-midi-api/#midiinputmap-interface
OpenedJan 24, 2014
http://webaudio.github.io/web-midi-api/
(TR version has wrong Editors Draft link; I had to track it down on GitHub. http://www.w3.org/TR/webmidi/).
I have independently left some feedback on their repo before (issues here).
The attempts at making a Map-like class seem to have gone horribly awry: http://webaudio.github.io/web-midi-api/#midiinputmap-interface