Small recommendation for folks looking to use JS for Windows development (I understand this is just a runtime, but people may be inclined to combine these two things): do not use WinJS for any reason. It's undoubtably the worst UI "framework" I've ever used. Completely inflexible (HTML and styles defined in private and inaccessible methods, swallows events, monolithic functions) and riddled with bugs and incomplete features. Really surprised it's an official Microsoft project. I don't mean to disparage the developers of it, but it's really bad. Don't use it if you value your time or peace of mind and plan on customizing it in any meaningful way.