A new JavaScript Language Service in VS 2012 Update1. It will include a full-program Hindley-Milner type inferencing engine, similar to F#. The current C# compiler only supports method-based type inferencing.

Think of it as the Roslyn front-end AST implementation but only utilizing the C# 'dynamic' bits.

This will allow the Visual Studio front end to provide the 'smarts' needed for large program maintainability that Anders has previously identified as and issue. For example, better lint checking and industry-leading refactoring support.

As the Windows team commit to even better WinJS support, this is a vital component in the toolchain.