It would essentially involve changing the meaning of `: Type` and `as Type`. Basically, instead of ignoring type annotations at runtime, you'd have to throw whe

It would essentially involve changing the meaning of `: Type` and `as Type`. Basically, instead of ignoring type annotations at runtime, you'd have to throw when a cast fails. This would also have other implications on the language design. Checking if an expression has a certain type at runtime would mean relying less on structural types to make these checks cheap. I've been thinking about this exact language a lot recently, but it would not be the same as Typescript. A superset of JavaScript which can be statically optimized based on type information. Fwiw, I don't think Assembly script is this language either. It's a completely different language than JavaScript with a superficially similar syntax.