ReplaceTitleCommand.php

<?php

namespace Drupal\views\Ajax;

use Drupal\Core\Ajax\CommandInterface;

/**
 * Provides an AJAX command for replacing the page title.
 *
 * This command is implemented in Drupal.AjaxCommands.prototype.viewsReplaceTitle.
 */
class ReplaceTitleCommand implements CommandInterface {
    
    /**
     * The page title to replace.
     *
     * @var string
     */
    protected $title;
    
    /**
     * Constructs a \Drupal\views\Ajax\ReplaceTitleCommand object.
     *
     * @param string $title
     *   The title of the page.
     */
    public function __construct($title) {
        $this->title = $title;
    }
    
    /**
     * {@inheritdoc}
     */
    public function render() {
        return [
            'command' => 'viewsReplaceTitle',
            'title' => $this->title,
            'siteName' => \Drupal::config('system.site')->get('name'),
        ];
    }

}