title: How to do HH:mm:ss subtraction in momentjs
body: <p>I have below code :</p>
  
  <pre><code>moment(moment("23:00:00", "HH:mm:ss").diff(moment("18:00:00", "HH:mm:ss"))).utc().format("HH:mm:ss");
  </code></pre>
  
  <p>produces o/p: 05:00:00 - 
  working correctly</p>
  
  <pre><code> moment(moment("00:00:00", "HH:mm:ss").diff(moment("18:00:00", "HH:mm:ss"))).utc().format("HH:mm:ss");
  </code></pre>
  
  <p>it produces wrong o.p: 00:00:00:</p>
  
  <p>i need an below o/p: -18:00:00</p>