JQuery中Checkbox的一些功能

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script type="text/javascript" src="jquery.js"></script>

<script type="text/javascript">
$(function(){
   $(":checkbox").attr("checked",false);
             $(":checkbox:eq(0)").click(function(){
    if($(":checkbox:first").is(":checked"))
    {
     $("input:checkbox").attr("checked",true);
    }else
    {
      $("input:checkbox").attr("checked",false);
    }
    });
    $(":button:eq(0)").click(function(){
     $("input:checkbox[name=xuanx]").attr("checked","checked");
    });
    $(":button:eq(1)").click(function(){
     $("input:checkbox").attr("checked",false);
    });
    $(":button:eq(2)").click(function(){
    $(":checkbox[name=xuanx]").each(function(){
      if($(this).attr("checked"))
      {
       $(this).removeAttr("checked");
      }else
      {
       $(this).attr("checked",true);
      }
     });

    });

    $(":button:eq(3)").click(function(){
    var result="您当前的选项是：";
    $(":checkbox[name=xuanx]:checked").each(
     function(){
       result+=$(this).val()+" ";
      }
    )
     alert(result);

    });
  })
</script>
</head>