SetValueIfEmptyCommand.php
<?php
declare(strict_types=1);
namespace Drupal\my_module\Ajax;
use Drupal\Core\Ajax\CommandInterface;
/**
* Ajax command: fill empty form elements with a predefined value.
*
* This command targets one or more form elements via a CSS selector and sets
* their value only if the current value is empty (after trimming).
*
* The command also triggers `input` and `change` events so Drupal behaviors and
* other listeners react as if the user entered the value manually.
*/
final class SetValueIfEmptyCommand implements CommandInterface {
/**
* The Ajax command name used by Drupal.AjaxCommands.
*/
public const COMMAND = 'setValueIfEmpty';
/**
* Default selector used when none is provided.
*/
public const DEFAULT_SELECTOR = '[data-my-fill-target]';
/**
* Creates a command instance.
*
* @param string $fillValue
* The value to set when the target element is empty.
* @param string|null $targetSelector
* CSS selector for the target elements. If omitted, DEFAULT_SELECTOR is used.
*/
public function __construct(
protected string $fillValue,
protected ?string $targetSelector = null,
) {}
/**
* {@inheritdoc}
*/
public function render(): array {
return [
'command' => self::COMMAND,
'selector' => $this->targetSelector ?? self::DEFAULT_SELECTOR,
'value' => $this->fillValue,
];
}
}
media_fill_if_empty.js
/**
* @file Field empty check.
*/
(function (Drupal) {
'use strict';
Drupal.AjaxCommands.prototype.setValueIfEmpty = function (ajax, response) {
const targetSelector = response && response.selector ? response.selector : '';
const fillValue = response && typeof response.value === 'string' ? response.value : '';
if (!targetSelector) {
return;
}
const elements = document.querySelectorAll(targetSelector);
for (const element of elements) {
let currentValue = '';
if (typeof element.value === 'string') {
currentValue = element.value.trim();
}
else if (element.isContentEditable) {
currentValue = (element.textContent || '').trim();
}
if (currentValue !== '') {
continue;
}
if (typeof element.value === 'string') {
element.value = fillValue;
}
else if (element.isContentEditable) {
element.textContent = fillValue;
}
else {
continue;
}
element.dispatchEvent(new Event('input', { bubbles: true }));
element.dispatchEvent(new Event('change', { bubbles: true }));
}
};
})(Drupal);my_module.libraries.yml
set_value_if_empty:
js:
js/set_value_if_empty.js: {}
dependencies:
- core/drupal
- core/drupal.ajaxMyResponse.php
use Drupal\Core\Ajax\AjaxResponse;
use Drupal\my_module\Ajax\SetValueIfEmptyCommand;
$response = new AjaxResponse();
// Example: fill a media name field if it's empty.
$fill_value = 'foo-bar';
// Selector for a specific element in this use-case.
$target_selector = '[data-drupal-selector$="my_field"]';
$response->addAttachments([
'library' => [
'my_module/set_value_if_empty',
],
]);
$response->addCommand(new SetValueIfEmptyCommand($fill_value, $target_selector));
return $response;
23.10.2026 | Lothar Ferreira Neumann
