AlertCommand.php

<?php

namespace Drupal\Core\Ajax;


/**
 * AJAX command for a javascript alert box.
 *
 * @ingroup ajax
 */
class AlertCommand implements CommandInterface {
    
    /**
     * The text to be displayed in the alert box.
     *
     * @var string
     */
    protected $text;
    
    /**
     * Constructs an AlertCommand object.
     *
     * @param string $text
     *   The text to be displayed in the alert box.
     */
    public function __construct($text) {
        $this->text = $text;
    }
    
    /**
     * Implements Drupal\Core\Ajax\CommandInterface:render().
     */
    public function render() {
        return [
            'command' => 'alert',
            'text' => $this->text,
        ];
    }

}