com_ajax to plugin / or plugin field

Question

I have this customfield plugin where the user can select a folder in a popup, the call should be ajax based. The form-"field" including AJAX call etc. works already in some of my modules where the Ajax call goes via com_ajax into the module class and calls there MethodNameAjax. But i'm not able to bring this to work in my customfield module...

Where do i have to write in my Ajax Response Point & how?

customfield.php:

class PlgFieldsCustomfieldname extends FieldsListPlugin{
   public function onCustomFieldsPrepareDom($field, DOMElement $parent, JForm $form){...}
}

then inside models/fields/modalfolderselect.php the formfield for the "selection":

class JFormFieldModalFolderSelect extends JFormField{
  protected function getInput(){ ... Field render ... }
  protected function getLabel(){ ... }
}

And the JS (for the modal and the AJAX Call from backend) /assets/modalfolderselect.js:

function getFilesystemAjax(path = ''){
    let data = {
        path:path,
    };
    let request = {
        'data': JSON.stringify(data),
        'format': 'json',
        'option':'com_ajax',
        'group': 'fields', (also tried 'Fields' here)
        'plugin': 'customfieldname',
        'method': 'listfilesystem'
    };
    return jQuery.ajax({
        url: '/index.php',
        type : 'GET',
        data: request,
        dataType:'json'
    });
}

My problem now is, the plugin itself is not of type "Ajax" and it does not has to be because it is a customfield that has to extend FieldsListPlugin - and also the form field itself is has to extend JFormField... So i've found a hint that you can send the "group" as query option - unfortunately this is not enough. I need at least a simple example code how the AJAX call into a plugin in this scenario will work...

At least i've tried to put in this methods on various locations in my code without any response / error log at all.

public ?static? function onAjaxListfilesystem(){
        error_log("AJAX Call!");
        return "Ajax Call!";
}

Answer 1

Plugins don't use method parameter. Instead the value you currently have there should be used in plugin parameter. This is because com_ajax dispatches an event rather than calling a specific method of a specific plugin. So the request data should be this:

let request = {
    'data': JSON.stringify(data),
    'format': 'json',
    'option':'com_ajax',
    'group': 'fields',
    'plugin': 'listfilesystem'
};