append为内部插入
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
<script src="js/jquery-3.3.1.js"></script>
</head>
<body>
<p id="content">I love </p>
<script>
$("#content").append("<span>you.</span>");
//或者写为 $("<span>you.</span>").appendTo("#content");两者效果一样
</script>
</body>
</html>
显示输出为 I love you.
