<html lang="en">
<head>
<meta charset="UTF-8">
<title>bootstrap4</title>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css">
<link href="https://cdnjs.cloudflare.com/ajax/libs/summernote/0.8.9/summernote-bs4.css" rel="stylesheet">
</head>
<body>
<textarea id="summernote"></textarea>
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.11.0/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/js/bootstrap.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/summernote/0.8.9/summernote-bs4.js"></script>
<script>
$('textarea#summernote').summernote();
</script>
</body>
</html>