选取指定类型(p)父元素下的第几个子元素:
实例:
<!DOCTYPE html>
<html lang='zh-cn'>
<head>
<title>Insert you title</title>
<meta http-equiv='description' content='this is my page'>
<meta http-equiv='keywords' content='keyword1,keyword2,keyword3'>
<meta http-equiv='Content-Type' content='text/html; charset=utf-8'>
<script type='text/javascript' src='./js/jquery-1.12.1.min.js'></script>
<style type='text/css' >
*{margin:0;padding:0;}
html{font:400 15px/1.2em 'Courier New';color:#666;}
div > *{margin:10px 0;cursor:pointer;}
#demo{750px;margin:75px auto;}
button{padding:5px 15px;border:0;outline:none;margin-top:-5px;border-radius:2px;font:400 12px/1.2em 'Courier New';}
.active{background-color:yellow;transition: .3s;}
.hover{background-color:red;transition: .3s}
p{text-indent:8px;}
</style>
<script type='text/javascript'>
/**
概述
选择同属于一个父元素之下，并且标签名相同的子元素中的第n个。
因为jQuery的实现:nth-是严格来自CSS规范，n值是“1-indexed”，也就是说，从1开始计数。对于所有其他选择器表达式比如:eq()或 :even ，jQuery遵循JavaScript的“0索引”的计数。
*/
$(function(){
$("span:nth-of-type(2)").addClass('hover');
});
</script>
</head>
<body>
<div id='demo'>
<div>
<span>John</span>
<b>Kim</b>
<span>Adam</span>
<b>Rafael</b>
<span>Oleg</span>
</div>
<div>
<b>Dave</b>
<span>Ann</span>
</div>
<div>
<i><span>Maurice</span></i>
<span>Richard</span>
<span>Ralph</span>
<span>Jason</span>
</div>
</div>
</body>
</html>