Could we have TypeScript with no build step? Could we have types in JavaScript? Maybe! We're exploring bringing optional type syntax into the JavaScript language! devblogs.microsoft.com/typescript/a-p…

@typescript For a type system, but comments are for humans. Have another iteration for a proper extension of the ECMAScript syntax, take inspiration from other modern languages such as Rust, Dart, Swift, as well TypeScript. I really think it could be great, but not with comment hacks! :)