Just to see how the google reCatcha works i did a small POC. This POC used jquery in front end and node js at backend.

The frontend app is hosted at : http://ill-informed-hall.surge.sh/ The backend app is hosted at : https://myapp-wxosimgzsb.now.sh/

Backend application is maintained in Bitbucket as it provides private repository for free. The objective of maintaining backend code in private repository is because google won't recommend to expose the secret key (Used for authentication) to expose.

The app is based on the learning did from here. The keys are maintained under Nikhil's gmail Id