sfHover = function() {
  var sfEls = document.getElementById('nav').getElementsByTagName('li');
  for (var i=0; i<sfEls.length; i++) {
    sfEls[i].onmouseover=function() {
      this.className+=' sfhover';
    }
    sfEls[i].onmouseout=function() {
      this.className=this.className.replace(new RegExp(' sfhover\\b'), '');
    }
  }
}
window.onload=sfHover;