title: add td element to tr with id
body: <p>Pretty much what the title says. I have html documnet with</p>
  
  <pre><code>&lt;table&gt;
    &lt;tr&gt;
      &lt;td id="1"&gt;&lt;/td&gt;
    &lt;/tr&gt;
  &lt;/table&gt;
  </code></pre>
  
  <p>setup and want a javascript function to add <code>&lt;td id="2"&gt;&lt;/td&gt;</code> under the previous one so it looks like.</p>
  
  <pre><code>&lt;table&gt;
    &lt;tr&gt;
      &lt;td id="1"&gt;&lt;/td&gt;
      &lt;td id="2"&gt;&lt;/td&gt;
    &lt;/tr&gt;
  &lt;/table&gt;
  </code></pre>