title: Javascript MutationObserver Error
body: <p>The following script works, but chrome says that there is an error..<br />
  What should I do to solve this error?</p>
  
  <pre><code>function Do(){alert("test");}
  
  new MutationObserver(Do).observe(document.body,{childList:true,subtree:true}); //works, but there's error.
  </code></pre>
  
  <p>The error message in chrome console is this;</p>
  
  <blockquote>
    <p>Uncaught NotFoundError: An attempt was made to reference a Node in a
    context where it does not exist. (anonymous function)</p>
  </blockquote>