[c-hendricks]

Conversely, TypeScript is my favourite type system because it has to support the wild things people did in untyped languages.

[awepofiwaop]

The issue with TS is that it's not really a type system, it's mostly just comments with a linter bolted on. It tries, but it's fundamentally broken in too many ways.

Here's just one very simple example, there are many more. I've checked all the strict mode options and this appears to still "typecheck".

  var x: {a: number} = {a: 1};
  var y: {a: number|string} = x;
  y.a = 'FAIL';
  var n: number = x.a; // not actually a number

Source: https://www.typescriptlang.org/play/?noUncheckedIndexedAcces...

[koito17]

Two things to note:

1. TypeScript doesn't aim to have a sound type system. i.e. there may be things the type system accepts that are actually unsafe.

2. this is more of an issue with mutation. If those properties were marked `readonly`, then the assignment of y.a wouldn't work at all. You can also encapsulate mutation behind functions with your intended types.

I tend to write TypeScript in a "functional" or "immutable" way, and in this case, most soundness issues come from things like array index access, which can't really be solved without dependent types anyway.

With that said, TypeScript still gets one quite far *despite* soundness not being a goal of the type system. The problem is that writing imperative, mutable code will make you go through (intentionally!) unsound covariance of types. Similar issues exist for code with side effects, since TypeScript has no way to encode effects in the type system. This is why some language communities settle on ideas like "functional core, imperative shell", where the ultimate goal is absolute minimum amount of code involved in side effects and mutation, while everything else is designed to be easy to test (and, ideally, expressible with a sound subset of your type system).

[siwatanejo]

Haha, it is actually my least favorite statically typed lang for this very reason.

[awepofiwaop]

I agree. The sheer amount of flexibility it provides makes it both hard to use/read and also not particularly safe/sound. No other type system in existence allows you to be as incoherent as TS.

[throwaway81523]

You didn't like Purescript? It looked pretty cool to me. Its main competition back in the day was Elm, but Typescript has now taken over. From a distance Typescript seems to have too many gaps. I haven't used it though.

[rapnie]

The Lustre [0] web framework in Gleam was directly inspired by Elm.

[0] https://github.com/lustre-labs/lustre

[culi]

I think TypeScript can feel like there's too many gaps because not enough people take it seriously enough to truly learn it. Hardly anyone reads a book about best practices/design the way many do about C/Java/Rust.

It's actually a very powerful tool when used thoughtfully. Although it wasn't the first structurally typed language I tried, it's the one that made me fall in love with structural type systems

[galaxyLogic]

I like the strutural typing as well. But I hesitate to use TypeScript because AI tells me this:

It Catches: Mismatched function arguments, missing object properties, and typos in variable names.

It Misses: Invalid JSON from an API, unexpected database outputs, and bad user input.

[culi]

You use Zod if you want runtime features. I'd say it's pretty industry standard. On the type level there's no reason it couldn't account for any of the examples you pointed out. And since Zod supports all the expressiveness of the actual language, you can certainly have those as runtime checks

I would also just like to point out that the "It Misses" your robot pointed out aren't actually flaws with TypeScript but flaws with JavaScript.