TypeScript definition files

In addition to what @Christoffer has said for the DOM, @Boris Yankov has a really useful repository here: https://github.com/borisyankov/DefinitelyTyped with definition files for more than thirty, one hundred and thirty close to two hundred libraries(and counting!).

There's even a manager for the type definition files now: http://definitelytyped.org/tsd/ (Do not follow: link is now NSFW spam)

AND: Quite a lot of definition files are now on nuget: http://www.nuget.org/packages?q=TypeScript

The lib.d.ts that is included in the source (http://typescript.codeplex.com/SourceControl/changeset/view/fe3bc0bfce1f#bin%2flib.d.ts) contains definitions for most of the DOM related stuff. If you are using Visual Studio, you should consider downloading the tools which includes a template where lib.d.ts is bundled.

If anything is missing, I think you can use the declare syntax.