Ask HN: Is there any apps out there built using single lang for the whole stack?

I am working on a web app and thinking of using javascript (react, node, express, mongo etc) as only language for full stack of this app. Is there any apps out there (preferably the ones you worked on) that are using single language (javascript, python, ruby etc) for the full stack of the app? And what are pros and cons you faced building the stack in same language?