Pushing react/expressJS app to Heroku

I have a simple React/ExpressJS app that I would like to push to Heroku. On my local machine I use webpack to build the app.

In my .gitignore file I ignore the /build directory mainly because they do this when using create-react-app

My question is do I push everything up to Heroku and let it build the app again once it's pushed up or do I build locally and then push everything up (including all the src files)?

via tommyd456