Gives the same impression as less and we use that one too for building our styles.
This is the feature I like most, duck typing at its core. Just define what you are expecting and the compiler will check this for you. The Microsoft TFS team converted their web client to use TypeScript and already fixed 13 bugs that they didn’t know existed before, while they still have unit tests, integration tests and no jslint errors.
More info: http://www.typescriptlang.org/ (with a play ground in the browser)