Select an element by its index without jquery
<p>I have nothing but only this useless code:</p>

<pre><code>document.getElementsByClassName('dynamic_area').index(input+4);
</code></pre>

<p>What is my mistake?</p>

<p>Important:</p>

<ul>
<li><p>Don't use jQuery,</p></li>
<li><p><code>input</code> is a variable</p></li>
</ul>
