Make Web MIDI API listen to a specific channel

Question

I am making a proyect where I'm using the web MIDI API and a loopback MIDI port, but I want to know if there is any way tomakeit listen to different channel other than the first?

Here is my code:

var notes=[]
navigator.requestMIDIAccess()
    .then(onMIDISuccess, onMIDIFailure);

function onMIDISuccess(midiAccess) {
    for (var input of midiAccess.inputs.values()){
        input.onmidimessage = getMIDIMessage;
    }
}

function getMIDIMessage(message) {
    var command = message.data[0];
    var note = message.data[1];
    var velocity = (message.data.length > 2) ? message.data[2] : 0; // a velocity value might not be included with a noteOff command
    console.log(message)

    switch (command) {
        case 144: // noteOn
            if (velocity > 0) {
                noteOn(note, velocity);
            } else {
                noteOff(note);
            }
            break;
        case 128: // noteOff
            noteOff(note);
            break;
    }
}

function onMIDIFailure() {
    console.log('Could not access your MIDI devices.');
}

Also, I haven't seen any property in the MIDI messages related to the channels, so I really don't know how to do it.

Answer 1

The channel is encoded in the first byte. If the value is 144 it means the message is for the first channel. A value of 145 would be for the second channel. Up to 159 which is a note on message for the 16th channel.

The same principle applies to note off messages. A value of 128 is for the first channel. A value of 129 is for the second channel. ...

You can get the index of the channel with a binary operation like this:

const channelIndex = message.data[0] & 0x0F;

The type of event can be checked by shifting the value by four bits.

const eventType = message.data[0] >> 4;

A value of 8 would be a note off message. A value of 9 is a note on message.