How to use the pouchdb-binary-utils.blobOrBufferToBinaryString function in pouchdb-binary-utils

binaryMd5(att.data, function (md5) {
    att.digest = 'md5-' + md5;
    // size is for blobs (browser), length is for buffers (node)
    att.length = att.data.size || att.data.length || 0;
    if (blobType === 'binary') {
      blufferToBinaryString(att.data, function (binString) {
        att.data = binString;
        callback();
      });
    } else if (blobType === 'base64') {
      blufferToBase64(att.data, function (b64) {
        att.data = b64;
        callback();
      });
    } else {
      callback();
    }
  });
}