为什么执行结果都是元素的长度=0？
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8" />
<title></title>
<link rel="stylesheet" href="imooc.css" type="text/css">
<script src="http://libs.baidu.com/jquery/1.9.1/jquery.js"></script>
</head>
<body>
<h2>可见性筛选选择器</h2>
<h3>:visible/:hidden</h3>
<div class="left">
<div class="div">
<a>display</a>
<p id="div1" style="display:none;">display</p>
</div>
<div class="div">
<a>width</a>
<a>height</a>
<p id="div2" style="width:0;height:0">width/height</p>
</div>
<div class="div">
<a>visibility</a>
<a>opacity</a>
<p id="div3" style="visibility:hidden;opacity:0">visibility</p>
</div>
</div>
<p id="show"></p>
<script type="text/javascript">
function show (ele) {
if (ele instanceof jQuery) {
$("#show").html('元素的长度的 = ' + ele.length)
} else {
alert(ele+' 不是jQuery对象')
}
}
</script>
<script type="text/javascript">
//查找id = div1的DOM元素,是否可见
show( $('#div1:visible') );
</script>
<script type="text/javascript">
//查找id = div2的DOM元素,是否可见
show( $('#div2:visible') );
</script>
<script type="text/javascript">
//查找id = div3的DOM元素,是否可见
show( $('#div3:visible') );
</script>
<script type="text/javascript">
//查找id = div1的DOM元素,是否隐藏
show( $('#div1:hidden') );
</script>
<script type="text/javascript">
//查找id = div2的DOM元素,是否隐藏
show( $('#div2:hidden') );
</script>
<script type="text/javascript">
//查找id = div3的DOM元素,是否隐藏
show( $('#div3:hidden') );
</script>
</body>
</html>
