//**dataURL to blob**

    function dataURLtoBlob(dataurl) {

        var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],

            bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);

        while (n--) {

            u8arr[n] = bstr.charCodeAt(n);

        }

        return new Blob([u8arr], { type: mime });

    }

    //**blob to dataURL**

    function blobToDataURL(blob, callback) {

        var a = new FileReader();

        a.onload = function (e) { callback(e.target.result); }

        a.readAsDataURL(blob);

    }

    //test:

    //var blob = dataURLtoBlob('data:text/plain;base64,YWFhYWFhYQ==');

    //blobToDataURL(blob, function (dataurl) {

    //    console.log(dataurl);

    //});