<script type="text/javascript" charset="utf-8">
  function response(obj){
   var $list = $(obj);
   var $children = $list.children();
   var num= $children.size();//$list  总个数
   var current=0; //当前选中项
   addnow()
   $(document).bind('keydown',function(e){
    if($list.is(":visible")){
     if(e.keyCode == 40){ //向下
      if(current<num -1) current = current +1;
      addnow()
      e.preventDefault();
     }else if(e.keyCode ==38 ){//向上
      if(current > 0)current= current -1;
      addnow()
      e.preventDefault();
     }else if(e.keyCode == 13){
      var url = $children.eq(current).find('a').attr('href');
      document.location= url;
     }
    }else{
     current = 0;
     addnow()
    }
   });

   function addnow(){
    $children.eq(current).addClass('now').siblings().removeClass('now');
   }

  }

  response('#ul');