title: Getting Error: Object doesn't support property or method 'assign'
body: <p>I am using this jquery popup plugin <a href="https://web.archive.org/web/20170808060543/http://dixso.github.io:80/custombox/" rel="noreferrer">from this link</a> on my WordPress site. It's working fine on all browsers but giving the following error on IE11.</p>
  
  <p><a href="https://i.stack.imgur.com/exRCH.png" rel="noreferrer"><img src="https://i.stack.imgur.com/exRCH.png" alt="enter image description here"></a></p>