title: Datatables get filter text input string
body: <p>I have a Datatable that loads with new data every time the user changes the option from a dropdown list for which I want to keep the same filter even even if the table content changes. I've tried to get the current value from the search input by using:</p>
  
  <pre><code>$('div.dataTables_filter input').val() 
  </code></pre>
  
  <p>suggested in <code>https://datatables.net/forums/discussion/242/getting-filter-text</code></p>
  
  <p>or</p>
  
  <pre><code>table = $("#datatable-buttons").DataTable({...});
  table.fnSettings().oPreviousSearch;
  </code></pre>
  
  <p>but without any success :( Is there a way to get the filter input text?</p>