I was worried that MS would drop support for WinJS and double down on XAML. Allowing fully native builds for Windows Phone from Javascript instead of just native wrappers is great, now if only iOS and Android would follow suit.

They've just announced they are making WinJS cross-platform and open source (under Apache license). Now I haven't used WinJS, I haven't ever developed a WinRT app (just a few for the Phone), but doesn't WinJS have a ton of quality components, even more so than WinRT XAML? This seems pretty awesome.

I missed the cross platform part, I've been bouncing between the live stream and work this morning. So the claim is iOS apps with WinJS as if it had been built in Obj C with XIBs and not just a web view hosted in a native harness? If true that would be pretty amazing (it would probably also cause Xamarin to shit a brick)

No, definitely just a WebView. Still having a set of quality cross-platform MVVM-aware components for HTML5 is nice.

Oh, I misunderstood what the implications were for "cross platform" then in this context. I would never think that javascript wasn't cross platform, I'll have to look into the MVVM components but JS already has that with libraries like Knockout so obviously I need to go back and watch the keynote again.

Thanks for the clarification.

The APIs are what is now cross-platform. Previously WinJS had hooks for opening files (as one example) that obviously only worked in Windows.

Unless it is shoehorned into their appstore ... have they said anything about that?

Couldn't you do this with javscript before and also get MacOS, Linux, and Android? Anything with a web-browser?

win8's js framework isn't just a browser with your code in it. They expose pretty much all of their API surface to JS with JS-friendly APIs and things like promises for async calls, so you're not stuck using dumbed-down apis or calling out to native code shims for things HTML5 can't do yet.

No, web browsers don't have APIs for accessing everything the native platforms are capable of doing.