Untitled

<!DOCTYPE html>
<html lang="ja">
<head>
    <meta charset="utf-8" />
    <title>MutationObserver</title>
    <script src="domObserver.js"></script>
</head>
<body>
    <input type="button" value="Hello" onclick="appendTextNode()"/>
    <div id="text-container"></div>
</body>
</html>