Q: How to create .xml files with custom name with javascript?

I am currently encountering the following problem: I have an SQL query that brings me data and stores it in a table, when I click on a button, it executes a Javascript that exports the information of the table to a .XML, but when exporting it it gives a name to the file . This is the code segment:

function exportarDatosExcel(){

      var tab_text="<meta charset='UTF-8'><table border='2px'><tr bgcolor='#87AFC6'>";
      var textRange; 
      var j=0;
      tab = document.getElementById('casos'); // id of table

      for(j = 0 ; j < tab.rows.length ; j++) 
      {     
         tab_text=tab_text+tab.rows[j].innerHTML+"</tr>";
       //tab_text=tab_text+"</tr>";
      }

      tab_text=tab_text+"</table>";


      var ua = window.navigator.userAgent;
      var msie = ua.indexOf("MSIE "); 

      if (msie > 0 || !!navigator.userAgent.match(/Trident.*rv\:11\./))      // If Internet Explorer
      {
         txtArea1.document.open("txt/html","replace");
         txtArea1.document.write(tab_text);
         txtArea1.document.close();
         txtArea1.focus(); 
         sa=txtArea1.document.execCommand("SaveAs",true,"Contactos.xls");
      }  
      else //other browser not tested on IE 11
        sa = window.open('data:application/vnd.ms-excel,' + encodeURIComponent(tab_text));  
        return (sa);


    }

the file is saved but with a previously defined name. Any ideas or suggestions?