How to add new attributes for API

BinhQuang

I want add new attributes
protected function getDefaultAttributes($tag)
{
$attributes = [
'name' => $tag->name,
'description' => $tag->description,
'slug' => $tag->slug,
'color' => $tag->color,
'backgroundUrl' => $tag->background_path,
'backgroundMode' => $tag->background_mode,
'iconUrl' => $tag->icon_path,
'discussionsCount' => (int) $tag->discussions_count,
'position' => $tag->position === null ? null : (int) $tag->position,
'defaultSort' => $tag->default_sort,
'isChild' => (bool) $tag->parent_id,
'isHidden' => (bool) $tag->is_hidden,
'lastTime' => $this->formatDate($tag->last_time),
'canStartDiscussion' => $this->actor->can('startDiscussion', $tag),
'test' => $tag->test
];

    if ($this->actor->isAdmin()) {
        $attributes['isRestricted'] = (bool) $tag->is_restricted;
    }

    return $attributes;
}