TypeScript

TypeScript lets you write JavaScript the way you really want to.
TypeScript is a typed superset of JavaScript that compiles to plain JavaScript.
Any browser. Any host. Any OS. Open Source.

Ref:http://definitelytyped.org

Ref:http://www.typescriptlang.org

Ref:http://www.typescriptlang.org/Handbook

Ref:https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md