select2_json_from_api : allow callback for attribute

[rroblik]

Hi,

I'm using the new select2_json_from_api field and it's working great !

It should be cool to allow a callable callback in the attribute option, for example to concatenate 2 attributes of the json data in the drop down list 🆒, something like that :

'attribute' => function ($item) {
  return $item['name'] . ' (' . $item['id'] . ')';
}