I use html2canvas to export html elements to images. Now I am trying to export same canvas already generated by html2canvas to a pdf document using canvas2pdf but I am getting a blank pdf document.

<script>
   function getPdf() {
      var element = document.getElementById("qr-2");

        html2canvas(element).then(function(canvas) {

            var stream = blobStream();
            var ctx = new canvas2pdf.PdfContext(stream);

            ctx.stream.on('finish',
                function() {
                    var blob = ctx.stream.toBlob('application/pdf');
                    saveAs(blob, 'example.pdf', true);
                });
            ctx.end();
        });
    } 
 </script>