simple_midi_forwarder.js

// npm i easymidi esm && node -r esm simple_midi_forwarder.js

import { Input, Output, getInputs, getOutputs } from 'easymidi'

// these are lists of available devices
const inputs = getInputs()
const outputs = getOutputs()

console.log({ inputs, outputs })

// these will depend on your setup
const input = new Input(inputs[1])
const output = new Output(outputs[0])

const handler = ({ _type, ...params }) => {
  output.send(_type, params)
}

input.on('noteon', handler)
input.on('noteoff', handler)
input.on('poly', handler)
input.on('cc', handler)
input.on('program', handler)
input.on('channel', handler)
input.on('pitch', handler)
input.on('position', handler)
input.on('mtc', handler)
input.on('select', handler)
input.on('clock', handler)
input.on('start', handler)
input.on('continue', handler)
input.on('stop', handler)
input.on('reset', handler)
input.on('sysex', handler)