using parent.postMessage in c3runtime/actions.js

I have tried to use parent.postMessage but parent is undefined , also tried self.parent etc.

anyone know how to we to it in plugin, c3runtime/actions.js?

Thanks in advance

Also found that if I also have a script action on the event sheet along with the plugin action, the self.parent became defined.

What are you trying to do? Usually the parent global is only set if the document is running in an iframe. So it's normal that it's not set to anything if you're viewing it as a top-level page.