MIDI-controlled PTT in Discord

discord-midi-ptt.user.js

// ==UserScript==
// @name     Discord: MIDI controlled PTT
// @version  1
// @grant    none
// @match    https://discord.com/*
// ==/UserScript==

/*
 * This listens for any MIDI device sending a "note on" or "note off" event,
 * and rebinds this to F9.
 *
 * This should allow you to use any MIDI device as a way to activate Discord's
 * push-to-talk in the browser, even when it doesn't have focus!
 *
 * There's nothing specific in this script to Discord's UI, and should be
 * trivial to adapt to other sites.
 */

(() => {
	// We're going to send F9.
	const KEYCODE = 120;

	// MIDI command codes, we don't care which note.
	const NOTE_ON = 9;
	const NOTE_OFF = 8;

	// Send a keystroke to the page.
	function press(release) {
		document.activeElement.dispatchEvent(new KeyboardEvent(
			release ? 'keyup' : 'keydown', {keyCode: KEYCODE, bubbles: true, cancelable: true}));
	}

	navigator.requestMIDIAccess().then(
		(midi) => {
			// Listen on all MIDI input devices.
			const inputs = Array.from(midi.inputs.values());
			for (const input of inputs) {
				input.addEventListener('midimessage', (m) => {
					const cmd = m.data[0] >> 4;
					if (cmd == NOTE_ON) {
						press();
					} else if (cmd == NOTE_OFF) {
						press(true);
					}
				});
			}
		},
		(err) => console.log('midi fail:', err)
	);
})();