Typescript is my favourite language. Glad it's being continuously developed.
I really don’t see TypeScript destined for long term success with the rise of Wasm on the web. It is only where it is currently because it has operated at a huge advantage of being the only viable solution to a problem that every web developer has needed.
I say this as someone who writes a lot of typescript professionally and a lot of Dart for everything else I possibly can. The difference between the two is huge on almost every factor I can think of where Dart wins by a considerable margin. I’m thankful that Typescript existed at a time when it did but I don’t think it’s in anyway actually a good or sensible language (because it’s so closely to JavaScript) and I can’t wait to not have to use it in the future because better options exist and are becoming viable for more use cases.
Having used Swift and Kotlin in the past, their typesystems don’t come close to the flexibility with which you can wrangle data in TS. Many concepts that I would consider fundamental are either not present or require complicated syntax eg.: product types A & B, sum types A | B, { …spreading }.
And where Swift needs custom syntax such as `guard let` and `case let` to narrow types, Typescript is able to analyze normal control flow.
For practical reasons, there are a ton of ugly workarounds, but I’d rather live with those than go back to the rigid “Java++” languages.
But it's a double edged sword:
- You can brand types with additional information. For example, React Query does this to keep track of which type is stored under which cache-key. This is where most strongly typed languages just give up.
- You can progressively extend/narrow types without having to worry about inheritance. Invariants can be statically checked by encoding them in a type: eg IssuedInvoice = Invoice & { … }. A function that needs only a subset of a domain-object can specify this rather than requiring the email-address to verify a phone number.
- You can even emulate nominal types using keyed unions.
The first two alone have saved me from more errors than structural typing introduced.
those are intersection types and union types and are much more unique and rare in type systems eg all typed functional languages have product/sum types but typescript is the only mainstream language I know to have unions and intersection.