function login(){
    HttpSession Session = request.getSession();
    var aa = Session.getAttribute("MM_username");
    if(aa == ""){
          document.getElementById('top_2').style.display = "inline";
          document.getElementById('top_3').style.display = "none";
    }
    else{
          document.getElementById('top_2').style.display = "none";
          document.getElementById('top_3').style.display = "inline";
    }
}
.
.
.
<a href="javascript:login()" onclick="submit()">[登陆]</a>

<div id="top_2">222</div>
<div id="top_3">333</div>


这是个用dw做的用户登录，登陆之后top_2隐藏，top_3显示代码。没登陆时top_2显示 top_3隐藏的。请问哪里做得不对？
MM_username是存放登陆成功后的用户名