code: function listenOn (elements, event, callback) {
    if (elements instanceof Array) {
      elements.forEach((element) => {
        // If it's array inside array do recursive
        if (element instanceof Array) {
          listenOn(element, event, callback);
        } else {
          attachEventListener(element, event, callback);
        }
      });
    } else {
      attachEventListener(elements, event, callback);
    }
  }
docs: ./