I recently bought a Fitbit scale and spent a few hours trying their APIs. At the same time, I decided to open source the code I wrote. It's basically a Fitbit client library to talk to Fitbit.
Github repo of Fitbit-node
It's still a work in progress but the library is available as of now. It's not a lot of code and I am using npm package: OAuth.
When I get a chance, I'm going to add an example on how to use it.