TypeScript has quickly become my current favorite language. If you haven't heard of it yet then go here :
http://www.typescriptlang.org/
Why?
Any self respecting developer that does javascript work should definitely check it out. I really like the ideas in javascript and the ability to modify the language according to my liking but I really really miss the great tooling / typo checking we get with static typing.
I strongly suggest you look at Ander's talk here :
http://channel9.msdn.com/posts/Anders-Hejlsberg-Introducing-TypeScript (also embedded below) to get an idea of the awesomeness that becomes at your disposal:
Its open source. The tooling will be awesome. Developers, Developers, Developers.
Its better than CoffeeScript
In my opinion typescript is going to be as awesome for Javascript as LESS has proved to be for CSS. And in case you haven't heard of LESS its a superset of CSS that compiles down to CSS (example of popularity, twitter bootstrap uses it :
http://twitter.github.com/bootstrap/extend.html ). Similarly TypeScript is a Superset of Javascript, all your javascript is still valid TypeScript. Super Cool. You are not learning a new language, you are extending your knowledge of a language.
So to
learn typescript === learn javascript + more goodness
The community Loves it
The response from the community is what makes me really happy, and raises my faith in human support of all that is righteous and good :) . My measure of community response
Stackoverflow :
http://stackoverflow.com/questions/tagged/typescript And its not the number of questions they got in one month. Its the the number of votes on the accepted solutions. People are monitoring it a lot, in their own time. Always a good sign.
All your definitions are us
This is quickly becoming the definitive resource for all the typescript definitions your heart can desire :
https://github.com/borisyankov/DefinitelyTyped Love the open source