Saving dataURL(base64) to file on PhoneGap (android)

I'm converting canvas to dataURL(base64) type and I wanted to save it to phone filesystem using PhoneGap's writer but without success (I get broken file which I cannot open) - here's some of my code:

        var dataURL = document.getElementById("gen").toDataURL('image/png'); //substr() .replace('datadata:image/png;base64,', '');

         window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, gotFS, fail);
         function gotFS(fileSystem) {
            fileSystem.root.getFile("screenshot.png", {create: true, exclusive: false}, gotFileEntry, fail);
        }

        function gotFileEntry(fileEntry) {
            fileEntry.createWriter(gotFileWriter, fail);
        }

        function gotFileWriter(writer) {
            console.log("open and write");
            writer.seek(0);
            writer.write(dataURL);
            console.log("close and save");
        }

        function fail(error) {
            console.log(error.code);
        }

        var fileTransfer = new FileTransfer();
        fileTransfer.download("/", screenshot.png,  
            function(entry) {
                alert("download complete");
            },
            function(error) {
                alert("download error source " + error.source);
                alert("download error target " + error.target);
                alert("upload error code" + error.code);
            }
        );

I've tried also other solution from stackoverflow, which was based on addtional java plugin but it hasn't work for me. Is there pure JS(with additional js libs) solution for it?