Problem to download image on html2canvas by iPad tablet

The method below downloads a generated image, which works in Chrome and Firefox, but does not work in Safari using a tablet over the iPad, how do I download it?

$scope.downloadFile = function() {

    html2canvas($("#stage"), {
        onrendered: function(canvas) {
            //document.body.appendChild(canvas);
            canvas.toBlob(function(blob) {
                saveAs(blob, $scope.content.filename);
            });
        }
    });
};

html2canvas library and FileSaver