AnnounceCommand.php

<?php

namespace Drupal\Core\Ajax;

use Drupal\Core\Asset\AttachedAssets;

/**
 * AJAX command for a JavaScript Drupal.announce() call.
 *
 * Developers should be extra careful if this command and
 * \Drupal\Core\Ajax\MessageCommand are included in the same response. By
 * default, MessageCommand will also call Drupal.announce() and announce the
 * message to the screen reader (unless the option to suppress announcements is
 * passed to the constructor). Manual testing with a screen reader is strongly
 * recommended.
 *
 * @see \Drupal\Core\Ajax\MessageCommand
 *
 * @ingroup ajax
 */
class AnnounceCommand implements CommandInterface, CommandWithAttachedAssetsInterface {
    
    /**
     * The assertive priority attribute value.
     *
     * @var string
     */
    const PRIORITY_ASSERTIVE = 'assertive';
    
    /**
     * The polite priority attribute value.
     *
     * @var string
     */
    const PRIORITY_POLITE = 'polite';
    
    /**
     * The text to be announced.
     *
     * @var string
     */
    protected $text;
    
    /**
     * The priority that will be used for the announcement.
     *
     * @var string
     */
    protected $priority;
    
    /**
     * Constructs an AnnounceCommand object.
     *
     * @param string $text
     *   The text to be announced.
     * @param string|null $priority
     *   (optional) The priority that will be used for the announcement. Defaults
     *   to NULL which will not set a 'priority' in the response sent to the
     *   client and therefore the JavaScript Drupal.announce() default of 'polite'
     *   will be used for the message.
     */
    public function __construct($text, $priority = NULL) {
        $this->text = $text;
        $this->priority = $priority;
    }
    
    /**
     * {@inheritdoc}
     */
    public function render() {
        $render = [
            'command' => 'announce',
            'text' => $this->text,
        ];
        if ($this->priority !== NULL) {
            $render['priority'] = $this->priority;
        }
        return $render;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getAttachedAssets() {
        $assets = new AttachedAssets();
        $assets->setLibraries([
            'core/drupal.announce',
        ]);
        return $assets;
    }

}