Sending request to proxy server (Connecting front-end to back-end)

I'm trying to fetch JSON from darksky api (weather api) and according to its api, it is suggested to use a proxy server. I want to implement this using a nodejs proxy server demonstrated here: https://gist.github.com/davemo/4027855. If I already have the user's lat&long coordinates, how do I pass this to the nodejs server on the backend?

via Owen Chak