Toggle display UL element

Toggle display UL element

I'm stuck! Can't figure out what's wrong with this:

<ul id="menu" class='menu'>
   <li><a href='test'>Födelsedag</a></li>
   <li><a href='#' onclick='showSubmenu(1)'>Högtider</a><ul id="submenu1" class='menu submenu'>
   <li><a href='test'>Jul</a></li>
   <li><a href='test'>PÃ¥sk</a></li>
        </ul></li>
</ul>


My code:
function showSubmenu(menuId)
{
   $('#submenu'+menuId).style.display = 'block';
}


I get the error:
$("#submenu1").style has no properties


Please help