When I set out, a few years ago, to build a gui app in JS in Windows (but cross-platform), I found RingoJS which is a wrapper around Java. My entire app could be in a single .js file, with access to all Java libs. For the widget library, I chose SWT. I built a few very simple apps, despite having never programmed in Java before. Later, I found how to run my .js file directly with RhinoJS and SWT from the command line.
I'm pretty confident that this is the simplest way to build desktop apps in JS in Windows :)