Worth noting that webpack (via the webpacker gem) is supported in Rails 5.2, and will be default in Rails 6; using that gets you access to current versions of R

Worth noting that webpack (via the webpacker gem) is supported in Rails 5.2, and will be default in Rails 6; using that gets you access to current versions of React, Redux, and pretty much anything else packaged as npm modules. You still need some kind of view layer to serve up the pages that invoke the JS, but if what you're doing is a single-page app that's almost all React, then that view layer doesn't actually have to do very much.