Deploying Rails to Elastic Beanstalk, nodejs?

I want to host my app on a VPC EC2 instance with AWS, and this line in the documentation has me somewhat confused:

Install nodejs to allow the Rails server to run locally:

$ sudo apt-get install nodejs

I was just wondering why I need nodejs at all, let alone to allow the rails server to run locally since i thought that this was already handled by WEBrick.

Heres a link to the documentation in question:

http://ift.tt/1fa3chV