Is there a way that I can check if a data attribute exists?

if ($("#dataTable").data('timer')) {
  ...
}

NOTE this only returns true if the data attribute is not empty string or a “falsey” value e.g. 0 or false.

If you want to check for the existence of the data attribute, even if empty, do this:

if (typeof $("#dataTable").data('timer') !== 'undefined') {
  ...
}