node.js export to pdf system download folder

I've been working with node.js,the following function working fine in export to pdf.

but i want to this export file path sytem download folder path. i want to like this

for example: "c:/user/username/download"/filename.pdf";

Please help to how can i do it.

convertpdf :  function(req,res){
     var  wkhtmltopdf = require('wkhtmltopdf')
      var outputPDF =  "c:/temp/"+uniqueIDs+".pdf";

   _.map(exportDate, function(ep) {

        html = html + "<tr><td>" + ep.orderno +"</td><td>" + ep.amount +"</td><td>" +ep.milestoneid +"</td><td>" + ep.storyid +"</td><td>" + ep.date +"</td><td>" + ep.status +"</td><td>" + ep.description +"</td></tr>";
  });
   html = html + "</table></body></html>";
         wkhtmltopdf(html, {output: outputPDF}, function (err, result) {
             if(!err) {
                   message = "successFully exported to" + outputPDF ;
             return res.json({
                   message: message,
                    type: 'success'
            });
    }else {
           message = "unsuccessFull exported to pdf";
             return res.json({
                    message: message,
                     type: 'error'
               });
     }  
 }); // end of wkhtmltopdf 

please any one help me how can i solve this issue.

Thanks.