An alternative idea for a typed language living alongside/inside JavaScript

What if instead of trying to type existing JS code, like TypeScript, we made objects of a new typed language completely separate from JS objects? The TypeScript idea is to be able to type any old JavaScript that's out there. On the one hand this is admirable, but OTOH it leads to a very complicated type system. Here's an alternative idea: instead of typing existing, legacy JavaScript, treat it as…