How to set a downloading file name using window.open in javascript

Question

Hello I am very new to javascript. I am using the following code to export html table to xl file. It is working fine. But I am unable to set a file name. I searched for this got some solutions but nothing is working for me.

HTML Code:

<a onclick="fnExcelReport('customers');" href="#" download="your-foo.xls"> EXPORT </a>

Javascript Code:

function fnExcelReport(tableId)
        {
              var tab_text="<table border='2px'><tr bgcolor='#87AFC6'>";
              var textRange; var j=0;
              tab = document.getElementById(tableId); // 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>";
              tab_text= tab_text.replace(/<A[^>]*>|<\/A>/g, "");//remove if u want links in your table
              tab_text= tab_text.replace(/<img[^>]*>/gi,""); // remove if u want images in your table
                          tab_text= tab_text.replace(/<input[^>]*>|<\/input>/gi, ""); // reomves input params

                   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,"Say Thanks to Sumit.xls");
                              }  
                      else                 //other browser not tested on IE 11
                          sa = window.open('data:application/vnd.ms-excel,' + encodeURIComponent(tab_text));  


                          return (sa);
          }

Requirement: How to set downloading file name.

Your help will be appreciated. Thanks.