ble>
</div>

<p>Currently, options can be nested at the maximum third levels. (eg. user.name.first_name)</p>
<h1 id="specifying-callback-function">Specifying callback function</h1>
<p>Using callback is the common pattern of JavaScript, especially in Node.js.
You can add a comment for this like following:</p>
<pre><code class="language-javascript">/**
 * Asynchronous file open
 * @param {String} path the path to open
 * @param {String} flags flags for opening
 * @param {Number|String} [mode=&#39;0666&#39;] f