execCommand for SaveAs not working in Internet Explorer 9

Question

Below is function which I am using to save csv file using execCommand

function opensave() {

   var w = window.open('about:blank', '_blank');

   w.document.write(csvText);

   w.document.close();

   var success = w.document.execCommand('SaveAs',  true, 'test.csv');

   w.close();
} 

I am not able to see SaveAs dialog in IE 9

If I remove true from

w.document.execCommand('SaveAs',  true, 'test.csv');

SaveAs dialog opens, but I am seeing filename as untitled in SaveAs dialog.

How do I get filename as test.csv instead of untitled in SaveAs dialog ?

Thanks