So this is one area where I think TypeScript made a mistake: it added syntax that wasn't compatible with Javascript. This means you couldn't seamlessly support

So this is one area where I think TypeScript made a mistake: it added syntax that wasn't compatible with Javascript. This means you couldn't seamlessly support JS and TS with the same repo. Wouldn't comments be a better solution to this given the legacy? Here's what I think the type system should allow at a minimum: 1. Scalar types (number, string) 2. Common union types (eg something that could be a number or a string) 3. This is a big one: nullability should be part of the type system; 4. Object typing that includes mandatory and optional keys and their legal types; 5. Array types (generics); 6. Dictionary types (generics); and 7. An unknown type (like "mixed" in Hack). Part of this is you need the option of preserving types at runtime and doing runtime type enforcement. This should be optional to generate a "debug" build and can be stripped out. You should be able to assert types as well as turn on automatic type checking on entry and exit to function calls as a method of finding bugs. These errors should also be available as a warning (ie print to console.log) or an error (fatal). Lastly, you should be able to easily write a type error handler to capture such violations.