How to add additional class name to an element?
<p>I can't believe I can't find this in google - I need to add an additional class name to a <code>div</code> with the classname <code>checkField</code>:</p>

<pre><code>&lt;div id="wth" class="checkField"&gt;&lt;label&gt;Ok whatever&lt;/label&gt;&lt;/div&gt;

document.getElementById("wth").className="error"; // This works
document.getElementsByClassName("field").className="error"; // Doesn't work
</code></pre>

<p>I tried this:</p>

<pre><code>document.getElementsByClassName("field").getElementsByTagName("label").className="error";
</code></pre>

<p>^ Also doesn't work.</p>

<p>Can someone please give me some advice? I'm too use to JQuery.</p>
