There are numerous ways to get the IP address off of the request object.
The header x-forward-for will hold the originating IP address if a proxy is placed in front of the server. This would be common for a production build.
req.ips wwill hold an array of IP addresses in x-forward-for header. Client is likely at index zero
req.ip will have the IP address
req.socket.remoteAddress is an instance of net.socket which is used as another method of getting the IP address
req.ip and req.ips will work in express but not with other frameworks