grab form data in websockets - nodejs

I try to mix websockets, nodejs server and HTML5 API

On the front-end I have

var formData = new FormData();  
formData.append('file', files[0]);
formData.append('case', 'test');

so that I can grab an image and send it with using websockets like so

mysoc.send(formData)

My question is, on nodejs 0.10.12, how can I retrieve the form data, how can I do something like

$case=$_POST['case'];

Using php I can do it, but using javascript and nodejs I am lost. I am using the pg module but I found no similar example.

Any help?

Thanks