for jekyll templates - determine if item in menu is the current one navigated to

check-for-current.html

{% for item in sorted_items %}
    {% assign current = nil %}
        {% if page.id == item.url %}
          {% assign current = 'currentItem' %}
        {% endif %}
      <li class="{{current}}"><a href="{{item.url}}"><img src="{{item.imageId}}.jpg" /></a></li>
{% endfor %}