Display file "Open, save as" dialog before downloading the file

Display file "Open, save as" dialog before downloading the file

Hi,
 
I am trying for download files (doc, xls, pdf,ppt) using jQuery. I have the full path of the filename, which I am now passing to window.url.
 
Problem is the file is directly getting opened, but I would like to show the "Open, save as " Popup.
 
Below is the code used:
 
  1. // aspx
     <input type="button" id="filesDownload" value="Download" />
  3. // Sepearate JS file:
    $('#filesDownload).click(function () {
  4.         InvokeDownloader();
  5.     });

  6. function InvokeDownloader() {
             
                    var filename = currentItem.get_item('FileLeafRef');  // I get the Name of file
  7.                 var dir = currentItem.get_item('FileDirRef'); // I get the file path
  8.                 var imgfilename = dir + '/' + filename;
  9.                 window.location = imgfilename;
            }

How to show the "Open, Save as" dialog box and when user clicks on the save download the file?
 
Thanks