Max for Live,
in JavaScript

// 1. By PATH — positional, readable, but shifts if tracks move
new LiveAPI(null, "live_set tracks 0 devices 0");

// 2. By ID — a runtime handle Live hands you; stable *within* a session
new LiveAPI(null, "id", 42);

// 3. By a VIEW path — "what the user has selected right now"
new LiveAPI(null, "live_set view selected_track");

inlets  = 1;     // how many inlets the object box shows
outlets = 2;     // and how many outlets

// Handlers are matched by the *type* of the incoming message:
function msg_int(n)    { /* an integer arrived */ }
function msg_float(f)  { /* a float arrived     */ }
function bang()        { /* a bang arrived      */ }
function msg_symbol(s) { /* a single word       */ }
function list(a, b)    { /* a space-separated list */ }
function anything(sel) { /* anything else; sel = first word */ }

// Which inlet did it come in on?  ->  this.inlet  (0-based)

let lastFire = 0;
function msg_bang_action() {
    const now = Date.now();
    if (now - lastFire < 50) return;   // swallow burst replays
    lastFire = now;
    doTheDestructiveThing();
}

// trackvol.js — a minimal Max for Live device.
// Shows and controls the volume of the *currently selected*
// track, and updates live when you pick a different track or
// move the fader.
// Runs in a v8 object (Max 9 / Live 12.2+); the legacy js
// object works too.
autowatch = 1;   // reload on save while developing

inlets  = 1;     // inlet 0: a float 0.0–1.0 to set the volume
outlets = 2;     // outlet 0: track name  |  outlet 1: volume

// You CANNOT create a LiveAPI in global code — only inside a
// function, after Live has opened the Set.
let volumeObserver = null;
let volumePath     = null;

// A `live.thisdevice` object bangs once, when the device is
// fully loaded. Wire its bang to this script.
function init() {
    const view = new LiveAPI(onTrackChange, "live_set view");
    view.property = "selected_track";
    onTrackChange();   // prime it for whatever's selected now
}

function onTrackChange() {
    const t = new LiveAPI(null,
        "live_set view selected_track");
    if (t.id === 0) return;   // id 0 = "no object"

    // .get() ALWAYS returns an array: ["Drums"]
    outlet(0, "set", t.get("name")[0]);

    volumePath =
        "live_set view selected_track mixer_device volume";
    if (!volumeObserver)
        volumeObserver = new LiveAPI(onVolumeChange);
    volumeObserver.path     = volumePath;
    volumeObserver.property = "value";
}

// Fires whenever the volume changes — whether we set it,
// the mouse moved the fader, or automation did.
// args looks like ["value", 0.85].
function onVolumeChange(args) {
    if (args[0] === "value") outlet(1, args[1]);
}

// A float arriving on inlet 0 sets the current track's volume.
function msg_float(v) {
    if (this.inlet !== 0 || !volumePath) return;
    const vol = new LiveAPI(null, volumePath);
    vol.set("value", Math.max(0, Math.min(1, v)));
}

// A bang re-reads everything — handy behind a "refresh" button.
function bang() { onTrackChange(); }