title: How does Bootstrap convert class in Javascript with babel without using @babel/plugin-transform-classes
body: <p>Bootstrap is using classes here : 
  <a href="https://github.com/twbs/bootstrap/blob/master/js/src/button.js#L51" rel="nofollow noreferrer">https://github.com/twbs/bootstrap/blob/master/js/src/button.js#L51</a></p>
  
  <p>It doesn't seem that they are using plugin-transform-classes</p>
  
  <p><a href="https://github.com/twbs/bootstrap/blob/master/package.json#L109-L115" rel="nofollow noreferrer">https://github.com/twbs/bootstrap/blob/master/package.json#L109-L115</a></p>
  
  <p>I noticed they are using rollup though, but I don't think that is what is causing class to convert to es5 properly.</p>
  
  <p>Any ideas how they are achieving this?</p>