It seems to me that the type checking in TypeScript is extremely limited compared to what the Closure Compiler supports. The examples only show simple `fooInstance : Foo` examples, whereas Closure supports function prototype validation and such, a la C. I will need to see more elaborate examples.

Granted, there is no documentation that I could find on the website. I understand that this is a "preview," but I disagree with this way of presenting a tool. When the Closure Library was released, for instance, it was absolutely chock full of API documentation. This is because it was used for real-world projects and extensive docs mattered, even internal to Google.

There is a language specification (PDF, in the source tree) which is encouraging, but where's the manual? <http://www.floopsy.com/post/32453280184/w-t-f-m-write-the-fr.... The specification is largely a rewording of the ES5 spec with insertions where the typing additions are important. It will take a good bit for the reader to separate the wheat from the chaff, as they say.

I have more than a sneaking suspicion that this project is essentially a proof-of-concept, and that it is not heavily used at Microsoft. Do you remember "Microsoft Atlas" in 2006, at the height of the JS DOM Library Wars? In the end, they just pushed their developers to use jQuery with some code generation helpers. Microsoft's open-source track record for JavaScript is not impressive, and I think you'd be a damned fool to invest in this technology for any serious project.