How can i Duplicate a slide using office js?

I am trying to develop a powerpoint add-in using officejs and it seems the simplest of the things, duplicating a slide, is not available. Anyone faced this issue before and has found a workaround it ?

I have tried to add a new slide and copy all the shapes of the slide I want to copy. But it is not working. Also, when should we use .load() function and for what items ??

Thank you for your help.