title: jQuery - Append a Value to a INPUT, keeping it a Comma Delimited list
body: <p>I have an input like follows:</p>
  
  <pre><code>&lt;input type="hidden" id="attachment-uuids" value=""&gt;
  </code></pre>
  
  <p>I'd like to be able to append a value to the Input, at different times:</p>
  
  <pre><code>$('#attachment-uuids).val('55555');
  </code></pre>
  
  <p>results in:</p>
  
  <pre><code>&lt;input type="hidden" id="attachment-uuids" value="55555"&gt;
  </code></pre>
  
  <p>But then doing: </p>
  
  <pre><code>$('#attachment-uuids).val('66666');
  </code></pre>
  
  <p>results in:</p>
  
  <pre><code>&lt;input type="hidden" id="attachment-uuids" value="66666"&gt;
  </code></pre>
  
  <p>Where I'd like the following:</p>
  
  <pre><code>&lt;input type="hidden" id="attachment-uuids" value="55555, 66666"&gt;
  </code></pre>
  
  <p>how can I append values when the value is empty and when the value is not empty  with a comma delimited list?</p>
  
  <p>Thanks</p>