title: momentjs get time difference
body: <p>I am trying to get the time that user spent in a page with moment.js but it returns the wrong value.</p>
  <p>Code:</p>
  <pre><code>dateStart: any;
  
  ngOnInit() {
    this.dateStart = moment(); // current time
  }
  
  // when user post data before being redirect
  moment(moment(this.dateStart).diff(moment())).format(&quot;hh:mm:ss&quot;);
  </code></pre>
  <p>The code above supposed to return for instance <code>00:00:04</code> which means user was in this page for <code>4 seconds</code>. but I got something like this <code>06:59:55</code></p>
  <p>Any ideas?</p>