function msToTime(s) {

  // Pad to 2 or 3 digits, default is 2
  function pad(n, z) {
    z = z || 2;
    return ('00' + n).slice(-z);
  }

  var ms = s % 1000;
  s = (s - ms) / 1000;
  var secs = s % 60;
  s = (s - secs) / 60;
  var mins = s % 60;
  var hrs = (s - mins) / 60;

  return pad(hrs) + ':' + pad(mins) + ':' + pad(secs) + '.' + pad(ms, 3);
}

console.log(msToTime(55018))