jQuery 可见性过滤选择器

直接输入$(':visible')和$(':hidden')会有些好玩的东西；<div></div>是visible的，<span></span>是hidden的；<div />是visible的；

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
    String path = request.getContextPath();
    String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
%>
<!DOCTYPE html>
<html>
<head>
<base href="<%=basePath%>">
<meta charset="UTF-8">
<title>b index</title>
<link rel='stylesheet' type="text/css" href='b/css/bootstrap.css'>
</head>
<body style="margin:150px;">
    <h1>this is h1</h1>
    <div id="p1">
        <h2>this is h2</h2>
        <input type="text" >
        <div id="c1">1</div>
        <div id="c2">2
            <div id="cc21">21</div>
            <div id="cc22">22</div>
            <div id="cc23">23</div>
        </div>
        <div id="c3">3</div>
        <div id="c4">d4</div>
        <div id="c5">d5</div>
        <div id="c6"> </div><!-- 有一个空格:empty就找不到了 -->
        <div id="c7"></div>
        <div id="c71"><!-- 这种情况:empty也找不到 --></div>
        <div id="c8"><span></span><span>2</span></div>
        <div id="c9" style="display:none"></div>
    </div>
    <script type="text/javascript" src="js/jquery-1.11.1.js"></script>
    <script type="text/javascript" src="b/js/bootstrap.js"></script>
    <script type="text/javascript" src="js/index021.js"></script>
</body>
</html>