code: function (o, cb) {
      try {
        var reader = new FileReader();
        reader.onload = function (event) {
          cb && cb(reader.result);
        };
        reader.readAsText(o);
      } catch (error) {
        throw error
      }
    }
docs: Blob data convert to String
  @param o Blob obj
  @param cb callback function