How to implement a wrapper for the Javacript API of NodeJS in C++

I saw this website: appjs, and if you go to the end of it, you'll see the Section "We need your help!". Therein is explained that you could help by making wrappers for a specific plataform (whichever you want, be it Windows, Linux, Mac...) that should be an interface for the Javascript language so that the Javascript can call those functions (and obviously to create cross-plataform apps). So my question is and I can't find theory or explanations about how it works or who should I do it, to write something in C++, compile it, and then how the interface of that function can be called from outside, specifically from Javascript.

What should I know? Does the AppJS or the NodeJS have some kind of module programmed that allow that intercommunication between your own compiled C++ code and the JS part?

Basically how does wrapping works?

Thanks in advance.

Edit:

Probably, in the next couple of links there is information about the topic.

http://pravinchavan.wordpress.com/2013/11/08/c-binding-with-node-js/ http://es.slideshare.net/nsm.nikhil/writing-native-bindings-to-nodejs-in-c

Rather than "wrapping" the word that would fit the most would be "binding" I guess. Pthread (POSIX) is a "wrapper" but not a "binding".