The reason you wouldn't want a cross-compiler for that other language is that there are true semantic differences between languages, and many languages simply cannot fully support the JS runtime- and if your primary application is still in Typescript, trying to cross-compile for a single feature is downright ridiculous.

> The invention, support and defense of Typescript baffles me. It feels like an intensely wasteful work-around for poorly written interpreter error messages concocted by comp-sci grads who think compiled languages are superior to interpreted ones in all situations and they want to bring this wisdom to developers of loosely typed languages.

I sincerely don't think statically typed languages are superior, but I'd argue a large part of the increase in quality over the last few years of the ecosystem is due in large part to Typescript.

Is it going to fix all, or even a majority of the issues? Probably not. But if it can improve upon the situation I don't see why we'd make perfect the enemy of good.

Coming from a mostly C/C++ background, I had been very skeptical of “gradually typed” languages like Dart (and now Python), but I’ve come around to the view that for many purposes it’s better than a completely statically typed compiled language.

You don’t need to compile TS at all, just bundle it, which is lightning fast in current tools, so it feels almost as nimble as pure JS. But you have almost-instant type checking in tooltips and code completions, and you can run a full project check whenever you want (that’s slow, but still way faster than compiling Rust).

The type system isn’t perfect but it’s incredibly expressive. Almost anything you could imagine doing in straightforward JS can be typed (admittedly sometimes with a lot of effort and head-scratching) and once typed it’s generally easy to use with confidence that most runtime errors will be avoided.

The fact that JS and TS are separate languages is a bonus -- it keeps TS honest, and the competition between JS engines means runtime performance is great. If you were designing TS from scratch, I think you’d be tempted to add some kind of runtime type reification, but TS is better off without that. Completely erasing types means compilation will always be fast, and in my experience RTTI causes more architectural problems than it solves.