jQuery没有更改滚动菜单类

Question

这是jQuery

    // Cache selectors
var lastId,
topMenu = $("#cssmenu"),
topMenuHeight = topMenu.outerHeight()+75,
// All list items
menuItems = topMenu.find("a"),
// Anchors corresponding to menu items
scrollItems = menuItems.map(function(){
  var item = $($(this).attr("href"));
  if (item.length) { return item; }
}),
noScrollAction = false;

// Bind click handler to menu items
// so we can get a fancy scroll animation
menuItems.click(function(e){
var href = $(this).attr("href"),
    offsetTop = href === "#" ? 0 : $(href).offset().top-topMenuHeight+1;
noScrollAction = true;
$('html, body').stop().animate({ 
    scrollTop: offsetTop
},{
    duration: 300,
    complete: function() {
        menuItems
            .parent().removeClass("active")
            .end().filter("[href=" + href +"]").parent().addClass("active");
        setTimeout(function(){ noScrollAction = false; }, 10);
    }
});
e.preventDefault();
});

// Bind to scroll
$(window).scroll(function(){
if(!noScrollAction){
   // Get container scroll position
   var fromTop = $(this).scrollTop()+topMenuHeight;

   // Get id of current scroll item
   var cur = scrollItems.map(function(){
     if ($(this).offset().top < fromTop)
       return this;
   });
   // Get the id of the current element
   cur = cur[cur.length-1];
   var id = cur && cur.length ? cur[0].id : "";

   if (lastId !== id) {
       lastId = id;
       // Set/remove active class
       menuItems
         .parent().removeClass("active")
         .end().filter("[href=#"+id+"]").parent().addClass("active");
   }
   }    
});​

这是菜单的HTML

        <div id='cssmenu' style="z-index:1">
    <br><br><br><br><br>
        <ul>

            <li class="active"><a href='#image'><span>Home</span></a></li>
            <li><a href='#vote'><span>Vote</span></a></li>
            <li><a href='#donate'><span>Donate</span></a></li>

        </ul>

    </div>

问题是当我滚动时，菜单类没有改变。 jQuery应该改变＆＃34; li＆＃34;但似乎没有，我无法发现这个错误（ps我很抱歉，我是javascript的菜鸟）

提前谢谢！