.toString(radix) ?

i've written something like that

var reponse= {trame:"",longueur:0};

s.setup(9600,{rx:B6, tx:B5});
s.on('data', function(data) {
  reponse.trame+= data;
  if (reponse.trame.length >= reponse.longueur) {
    switch (reponse.trame.charCodeAt(1)) {
      case 0x01: // status
        console.log("status:",reponse.trame.charCodeAt(3));
        break;
      case 0x09: // status
        console.log("check Drive:",reponse.trame.charCodeAt(3));
        break;
      case 0x12: //Check the total numbers of audio in all folders(12)
        console.log("nbr total audios:",(reponse.trame.charCodeAt(3)<<8 ^ reponse.trame.charCodeAt(4)));
        break;
      case 0x0C: //Check the total audios(0C)
        console.log("nbr total audios:",(reponse.trame.charCodeAt(3)<<8 ^ reponse.trame.charCodeAt(4)));
        break;
      case 0x0D: //current audio
        console.log("nom fichier audio:",reponse.trame.charCodeAt(3),reponse.trame.charCodeAt(4));
        break;
      case 0x24: //duration audio
        console.log("Duréé: "+reponse.trame.charCodeAt(3)+"H "+reponse.trame.charCodeAt(4)+"mn "+reponse.trame.charCodeAt(5)+"s");
        break;
      default:
        break;
      }
  }
});

and each command sent, fill the reponse.longeur with the appropriate value...

function Duration() {
 var command = [0xAA, 0x24, 0x00, 0xCE];
  // Return: AA 24 03 hour minute second SM
  reponse.longueur = 7;
  reponse.trame = "";
  s.write(command);
}

Not Tested

Thanks for your help @allObjects.