There are several things under the TypeScript umbrella: a type system, language spec, JavaScript-targeting compiler and tooling that provides interactive code completion. I have tried TypeScript on a few small projects, the latest one being TypedPhoneGap. I also worked extensively with the language spec, wrote a parser and analyzer for the `.d.ts` contract specification fragment, pondered the semantics, and engaged in little flamewars on the language forum. My conclusion, in short, is this: the type system[...]