title: Why did I get [object HTMLParagraphElement]
body: <p>I am a newbie. Here is my code:</p>
  
  <pre><code>&lt;html&gt;
    &lt;head&gt;
      &lt;script type="text/javascript"&gt;
        function replyOne () {
          document.getElementById("comment_content").value = document.getElementById("username")
        }
      &lt;/script&gt;
    &lt;/head&gt;
    &lt;body&gt;
      &lt;p id="username"&gt;Jack&lt;/p&gt;
      &lt;textarea id="comment_content" &gt;&lt;/textarea&gt;
      &lt;button onclick="replyOne()"&gt;Copy Text&lt;/button&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>I expect that when I click the button, it will copy 'Jack' to the textarea. 
  But instead it just writes '[object HTMLParagraphElement]'.</p>