var nav_timeout = 500;
var nav_timer = 0;
var nav_menuitem = 0;

function nav_open(id) {
  nav_cancelclosetimer();
  if (nav_menuitem) nav_menuitem.style.visibility = 'hidden';
  nav_menuitem = document.getElementById(id);
  nav_menuitem.style.visibility = 'visible';
}

function nav_close() {
  if (nav_menuitem) nav_menuitem.style.visibility = 'hidden';
}

function nav_closetimer() {
  nav_timer = window.setTimeout(nav_close, nav_timeout);
}

function nav_cancelclosetimer() {
  if (nav_closetimer) {
    window.clearTimeout(nav_timer);
    nav_timer = null;
  }
}