title: How to remove class from siblings of an element without JQuery?
body: <p>I'm adding a class to an element and want to remove it from siblings. In JQuery it is simple, but how to do it the best way in plain JS?
  Here is an example of my code.</p>
  
  <pre><code>&lt;div class="controllers"&gt;
    &lt;span id='one' class='active'&gt;&lt;/span&gt;
    &lt;span id='two'&gt;&lt;/span&gt;
    &lt;span id='three'&gt;&lt;/span&gt;
  &lt;/div&gt;
  
  firstBtn.onclick = function() {
    slides[0].className = 'slide active';
    this.className = 'active';
  };
  </code></pre>