获取匹配的第一个元素:
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-3.0.0.js'></script> -->
<script type='text/javascript' src='./js/jquery-1.12.1.min.js'></script>
<style type='text/css'>
li{100%;height:20px;margin:10px 0;background:GreenYellow;font:400 13px/20px 'Courier New';color:#000;text-align:center;}
</style>
<script type='text/javascript'>
$(function(){
$('#list li:first').html('":first : "伪类选择器演示');
});
</script>
</head>
<body>
<ul id='list'>
<li></li>
<li class='active'></li>
<li></li>
<li></li>
</ul>
</body>
</html>