克隆元素
clone() 创建匹配结果及其后代和文本
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>unwrap</title>
<script src="https://ajax.aspnetcdn.com/ajax/jquery/jquery-3.3.1.min.js">
</script>
</head>
<body>
<div>
<ul id="ul">
<li>hgfd</li>
<li>gffd</li>
<li>hgfe</li>
<li>hgef</li>
</ul>
</div>
<button>克隆</button>
<script>
$('button').on('click', function () {
$li = $('#d').clone();
$li.insertBefore('#a');
});
</script>
</body>
</html>