[tacotacotaco]

Typescript won because is doesn’t ask developers to write better code, only that they write more code. As you pointed out, its syntax is familiar enough to be non-threatening to existing devs and its type system is completely optional in so far that I’ve worked with clients whose devs proudly proclaim their project is typescript yet they have _no_ types defined. Not that the type system is good anyway and I’m not even talking about `any`. That’s why it is so frustrating to me. Yes, we need a strong typed language but typescript’s type system is just disappointing, so of course it’s popular.

Typescript does make the devs _feel_ like it’s secure and that’s more important. Marketing works.

[satvikpendem]

Why is it disappointing? TypeScript's type system, via pseudo-dependent-types, is much more powerful than Elm's, Rust's, Haskell's etc. The only problem is that it's not sound, but JS itself is not sound, so TS can never be.

[creata]

> JS itself is not sound, so TS can never be.

What?

[danabrams]

The type system is not sound… that is there are things which the type checker cannot prove.

Not that the languages themselves are unsound.

[creata]

1. That's a horrible description of unsoundness; you're making it sound like incompleteness!

2. What I meant to ask was: what does satvikpendem mean by "JS is unsound"? It's a dynamically typed language, so they can't be talking about soundness in the type system...

[orta]

I did a bit of a writeup on the gaps in soundness for TypeScript in the docs, https://www.typescriptlang.org/play?strictFunctionTypes=fals...

[satvikpendem]

I should clarify, the JS type system is unsound, and because JS is valid TS, TS is by extension also unsound. Not sure why you'd think a dynamically typed language cannot be unsound, it still has types, they're just not static.

[creata]

Define soundness. Here's something close to the definitions that I've seen:

> The central result we wish to have for a given type-system is called soundness. It says this. Suppose we are given an expression (or program) e. We type-check it and conclude that its type is t. When we run e, let us say we obtain the value v. Then v will also have type t. - https://papl.cs.brown.edu/2014/safety-soundness.html

This only makes sense in the context of static types afaict, because you do not "typecheck an expression" in a dynamically typed language.

[satvikpendem]

Soundness is not decidability. The reason TS is unsound is not directly because it's undecidable, as any Turing complete system is undecidable, and the TS type system is Turing complete.

[demuxxed]

Typescript exists so you can press ‘.’ and find out what the npm library you just imported can do.

Types are more important/useful for library code than business/presentation logic. Typescript lets you can hire devs who can’t read documentation or understand type systems write javascript to stitch together enough imports to make something work.

[88913527]

Even if you aren't using types in first-party code, you're getting autocomplete and inline docs for all the third-party code, including the standard DOM API's, or NodeJS, or whatever types from your NPM modules. There's value in having that even if you live in a mostly `any`-typed codebase (which is likely more common than anyone's letting on).