title: Get offset from timezone
body: <p>I have a javascript timestamp and timezone ( "Europe/Stockholm" for example)</p>
  
  <p>How can I get difference from UTC? It can be seconds, or any other time unit.</p>
  
  <p>For example my timezone is UTC-2hrs, so I would get result of 7200sec.</p>
  
  <p>Any ideas?</p>