Yes, the combination of Windows Phone 8.1 and WinJs 2.1 will allow you to build cross platform WinJs based applications.
Universal apps written in Xaml also will be a very good way to share code across the two platforms with minimal changes.
Frage
I'm wondering if the Windows Phone 8.1 SDK supports WinJS? I saw there are some news that windows phone 8.1 start to support WinJS
If so, I will move to WinJS for WP and WinRT both.
Your comment welcome
Lösung
Yes, the combination of Windows Phone 8.1 and WinJs 2.1 will allow you to build cross platform WinJs based applications.
Universal apps written in Xaml also will be a very good way to share code across the two platforms with minimal changes.