ScrollTopCommand.php

<?php

namespace Drupal\Core\Ajax;


/**
 * Provides an AJAX command for scrolling to the top of an element.
 *
 * This command is implemented in Drupal.AjaxCommands.prototype.scrollTop.
 */
class ScrollTopCommand implements CommandInterface {
    
    /**
     * A CSS selector string.
     *
     * @var string
     */
    protected $selector;
    
    /**
     * Constructs a \Drupal\Core\Ajax\ScrollTopCommand object.
     *
     * @param string $selector
     *   A CSS selector.
     */
    public function __construct($selector) {
        $this->selector = $selector;
    }
    
    /**
     * {@inheritdoc}
     */
    public function render() : array {
        return [
            'command' => 'scrollTop',
            'selector' => $this->selector,
        ];
    }

}