> Javascript is a great language for building UIs

I disagree. It is easy to build something presentable with HTML and browsers, and there have been many JS frameworks that lower the barrier. However, that is not because JS is a good language for it; it is because JS is the only language available in that environment.

In fact, there are at least two other languages that transpile to JS, because you need JS to be able to run in a browser. But JS the language is not good enough, so you want two write your code in something else.

Building a UI in a completely different language, without a browser, is definitely harder, but you might have several advantages in the other, non-UI parts.

You haven’t made any arguments about why Javascript isn’t good for building UIs there. Here’s mine for why it is:

- first class functions (callback style is a good fit for UI programming)

- async/await and single threaded - many components of UIs are async by nature, Javascript supports you well here while keeping things simple with its single threaded model

Sharing the UI thread with logic is something to be mitigated when building UIs, it's not a feature.

In theory, maybe. In practice, your UI thread very rarely has to do the kind of heavy lifting that would block it so badly you actually have problems.

I have encountered this -- for example parsing very large incoming JSON payloads -- but very rarely. And if you really need to mitigate it, there are webworkers.

There's... a large number of languages with both of those features.

Could you name few better than js?

In the context of writing reliable software for a spacecraft? Pretty much anything with a reasonable type system, for a start. Maybe C#, or some reasonable subset of C++20, or Rust. Maybe Reason or OCaml.

I mean very clearly the good people at SpaceX have heard of these languages and decided against it. I think JS and Chromium are the best UI kit I can think of in terms of man hours to get X done. If you're careful the only thing I've ever had issues with is latency, but in space if you're in a situation where missing a frame or two is important you're already beyond fucked.

From my experience, Qt/QML is way better for things like that. I mean, the UI does not need to be responsive, does it?

Maybe they couldn't afford the Qt license.

Many people are using TypeScript these days, it works very well.

I like C# and Rust too. I've built UI's in C++ and MFC/OpenGL/DirectX. It remains my fairly strong opinion that JavaScript is well suited to UI development.

Javascript is a bad language period. For anything. It's used for UIs for historical reasons, not because it's good.

Javascript has also evolved quite a bit and there is also TypeScript that improves on that. The language is not perfect by any means, but it gets better.

I would expect the UI in a space ship to be soft realtime. Chromium and JS are anything but.

The only thing that's self-evident to me is that Javascript is a popular language for building UIs.