title: MutationObserver fails to observe textarea
body: <p>I'm trying to add custom undo operations to a textarea element by using a MutationObserver object.  I've looked on MDN for how to use this object, and as far as I know I seem to be using it correctly.  However, none of the mutations are registering - I want to observe whenever the text in the textarea changes.</p>
  
  <pre><code>function initObserver() {
      var editorObserver = new MutationObserver(function(mutations) {
          console.log("MUTATION");
  
          mutations.forEach(function(mutation){
              console.log(mutation.type);
          });
      });
  
      var editorObserverConfig = { characterData: true };
  
      var editor = document.querySelector("#editor");
  
      editorObserver.observe(editor, editorObserverConfig);
  }
  
  initObserver();
  </code></pre>
  
  <p>What might be wrong with this code?</p>