[ygra]

Out of curiosity, have there been features that were thought to be part of JS one day, added by TypeScript, and then abandoned for JS again, leading TS to rip them out as well? Or do such vestiges remain in TypeScript and have to be changed into different constructs on compilation?

[underwater]

TypeScript has incompatibilities with the private keyword and decorators. I don't think they have a strategy to deprecate.