Reveal.js MIDI plugin - presentation remote paging via Web MIDI API

reveal_midi.js

/*
 * reveal_midi.js
 * MIDI control plugin for reveal.js (http://lab.hakim.se/reveal-js)
 * MIT licensed
 *
 * Copyright (C) 2015 aike, http://github.com/aike
 */

(function() {
    var mode = 0;   // 0: note_on:left, note_off:right
                    // 1: note_on and even note_no:left, note_on and odd note_no:right
                    // mode 0 for iOS App "Web MIDI Browser" default page
                    // mode 1 for MIDI Keyboards

    var sendActiveSensing = false;
                    // send Active Sensing message(0xFE) to every 1000msec
                    // for connection check

    var midi = null;
    var inputs = [];
    var outputs = [];

    navigator.requestMIDIAccess().then(onMidiSuccess, onMidiFailure);

    function onMidiSuccess(m){
        midi = m;
        var it = midi.inputs.values();
        for(var o = it.next(); !o.done; o = it.next()){
            inputs.push(o.value);
        }

        it = midi.outputs.values();
        for(o = it.next(); !o.done; o = it.next()){
            if (o.value.name.match(/bluetooth/i)) {
                outputs.push(o.value);
            }
        }

        for(var i = 0; i < inputs.length; i++){
            if (mode === 0) {
                inputs[i].onmidimessage = onMidiEvent0;
            } else {
                inputs[i].onmidimessage = onMidiEvent1;
            }
        }
    }

    function onMidiFailure(msg){
        console.log("Midi Failure: " + msg);
    }

    function onMidiEvent0(event){
        if (event.data.length >= 3) {
            var note_no = event.data[1];
            if ((event.data[0] & 0xF0) === 0x90) {
                var velocity = event.data[2];
                if (velocity > 0) {
                    // note on
                    Reveal.left();
                } else {
                    // note off
                    Reveal.right();
                }
            } else if ((event.data[0] & 0xF0) === 0x80) {
                // note off
                Reveal.right();
            }
        }
    }

    function onMidiEvent1(event){
        if (event.data.length >= 3) {
            var note_no = event.data[1];
            if ((event.data[0] & 0xF0) === 0x90) {
                var velocity = event.data[2];
                if (velocity > 0) {
                    // note on
                    if (note_no % 2 === 0) {
                        Reveal.left();
                    } else {
                        Reveal.right();
                    }
                }
            }
        }
    }

    function activeSensing() {
        for (var i = 0; i < outputs.length; i++) {
            outputs[i].send([0xFE] , window.performance.now());
        }
    }

    if (sendActiveSensing) {
        setInterval(activeSensing, 1000);
    } 

})();