This is a calculator built with Rails, webpacker and react-rails. It saves recent calculations to local storage and allows the user to choose whether to evaluate the expressions in the frontend or backend.
You can visit this link to try the app in production (Give it a chance to load, it's running on a free Heroku dyno).
$ cd react-rails-app
$ bundle && yarn
$ foreman start -f Procfile.dev -p 3000