title: How to get elements with multiple classes
body: <p>Say I have this:</p>
  
  <pre><code>&lt;div class="class1 class2"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>How do I select this <code>div</code> element?</p>
  
  <pre><code>document.getElementsByClassName('class1')[0].getElementsByClassName('class2')[0]
  </code></pre>
  
  <p>That does not work.</p>
  
  <p>I know that, in jQuery, it is <code>$('.class1.class2')</code>, but I'd like to select it with vanilla JavaScript.</p>