This is a simple page and React app that lets a user bounce around a form, and when moving inputs, will try to save their work to the server. In this example, when the user blurs from an input, a call is made to the a remote action method with the Account record. If there is an error, the inputs are disabled and the error is displayed for the user; otherwise, nothing happens and the user may continue.
If you're interested in playing around with this page, it would be best to fork this repo and start working with the files in /dev/js/. You can run the following commands when in the repo's root folder to get started.
npm install
webpack --watch
Then as you make changes to your files in /dev/, you'll see them compiled into promises.resource/js/app.js, and can use MavensMate to deploy the resource bundle.