title: "parameter 1 is not of type 'Node'" when using MutationObserver
body: <p>I am a total noob at JS (as well as with the web development in general) :(</p>
  
  <p>Currently, I am working on a small script for Tampermonkey, which looks after specific elements in a particular class and plays a sound whenever any changes occur with the element. (Value changes, elements hides/shows, etc.).</p>
  
  <p>Currently, I have the following code:</p>
  
  <pre><code>     var audio = new Audio('URL_to_the_sound');
          var mutationObserver = new MutationObserver(function(mutations) {
        mutations.forEach(function(mutation) {
          console.log(mutation);
            audio.play();
        });
      });
      var target = document.getElementsByClassName('CLASSNAME');
          mutationObserver.observe(target, {
        attributes: true,
        characterData: true,
        childList: true,
        subtree: true,
        attributeOldValue: true,
        characterDataOldValue: true
      });
  </code></pre>
  
  <p>However, my browser responds with the following error:</p>
  
  <p><code>Uncaught TypeError: Failed to execute 'observe' on 'MutationObserver': parameter 1 is not of type 'Node'.</code></p>
  
  <p>I should mention that there are several elements in the same class.</p>
  
  <p>What should I do? :(</p>