Add defer or async attribute to dynamically generated script tags via JavaScript
<p>I am dynamically putting a script tag to the DOM of my page like this:</p>

<pre><code>var tag = document.createElement('script');
tag.src = "https://www.youtube.com/iframe_api";
var firstScriptTag = document.getElementsByTagName('script')[0];
firstScriptTag.parentNode.insertBefore(tag, firstScriptTag);
</code></pre>

<p>This should generate something like this:</p>

<pre><code>&lt;script src="https://www.youtube.com/iframe_api"&gt;&lt;/script&gt;
</code></pre>

<p>I just want to put in a <code>defer</code> or <code>async</code> to this script tag like this:</p>

<pre><code>&lt;script src="https://www.youtube.com/iframe_api" defer async&gt;&lt;/script&gt;
</code></pre>

<p>So how do I do this using JavaScript?</p>