This is a quick and dirty way of implementing CORS in a Rails app. DO NOT DO THIS IN A PROFESSIONAL SETTING

1. Go to app/controllers/application_controller.rb and comment out the protect_from_forgery line.
2. Go to your Gemfile and add the following line to the bottom : gem 'rack-cors', :require => 'rack/cors'
3. Run bundle
4. Go to config/application.rb and add the following code to the bottom of the Application class definition:

    config.middleware.use Rack::Cors do
      allow do
        origins '*'
        resource '*', :headers => :any, :methods => [:get, :post, :put, :patch, :delete, :options]
      end
    end

5. If you haven't already, restart the Rails server; then, serve up your front-end and start making requests!

Versions

Ruby : 2.2.0
Rails: 4.2.1
Bundler: 1.10.2
Postgres: 9.4.2.0