code: function (prefix, obj) {
              if (!obj.attr('id')) {
                  var generated_id;
                  do {
                      generated_id = prefix + '_' + randomNumber();
                  } while ($('#' + generated_id).length > 0);
                  obj.attr('id', generated_id);
              }
              return obj.attr('id');
          }
docs: return an element's id, after generating one when missing