Using 'nodobjc' a nodeJS->ObjectveC bridge to listen to distributed notification centre of macOS/OSX.

nodobjc-macOS-notification-listener.js

var $ = require('nodobjc')

$.framework('Foundation')
$.framework('AppKit')

var GetSongs = $.NSObject.extend('Delegate');

GetSongs.addMethod('getMySongs:', 'v@:@', function(self, _cmd, notif){
    var userInfo = notif('userInfo') 
    var keys = userInfo('keyEnumerator');
    var key;
    var song = {};
    
    while(key = keys('nextObject')){
        var value = userInfo('objectForKey', key)
        song[key.toString()] = value.toString();
    }
    console.log(song);
});

GetSongs.register();

var gs = GetSongs('alloc')('init');
var nc = $.NSDistributedNotificationCenter('defaultCenter');
var selector = $.NSSelectorFromString($('getMySongs:'));
var notification = $('com.spotify.client.PlaybackStateChanged');

nc(
    'addObserver', gs, 
    'selector', 'getMySongs:',
    'name', notification, 
    'object', null)

var app = $.NSApplication('sharedApplication');
function runLoop() {
  var pool = $.NSAutoreleasePool('alloc')('init');
  try {
    app('nextEventMatchingMask', $.NSAnyEventMask.toString(),
        'untilDate',             $.NSDate('distantFuture'),
        'inMode',                $.NSDefaultRunLoopMode,
        'dequeue',               1);
  } catch(e) {
    console.error('run loop error', e.message);
  }
  pool('drain');
  setTimeout(runLoop,1000);
  //process.nextTick(runLoop);
}

runLoop();