TypeScript 5.8 Beta Sneak Peek 🤫: This New Feature is AWESOME!

[@ThiagoOliveiraSantosfaren]

I've just had to write some overloads for this exactly problem last week. That's awesome to know that this'll no longer be a problem in version 5.8!

[@Typed-Rocks]

Awesome. I‘m also looking forward to it

[@dmitryts9093]

Could it be easier to create two types?

[@ThiagoOliveiraSantosfaren]

@ there're plenty of scenarios where you may create a single function that returns many different types according to its parameter with no additional logic. If you have opportunity to make code simpler, typescript shines giving precise return types

[@DirkLuijk]

Finally! Been waiting for this feature for a long time. Had to depend either on overloading (which doesn’t actually check whether the implementation is consistent with the overloading contract!), or a dirty type-cast.

[@malvoliosf]

This doesn’t sound like a feature so much as a bug fix. I would have thought that it would work in 5.7.

[@Typed-Rocks]

You have to check the pullrequest. There it is explained why it wasn‘t possible before. It „kinda“ is a bug but it is explainable why it was the case.

[@dzienisz]

TS is mostly fixing on bugs. I think feature set was done years ago.

[@keteremillpario]

Ts is a joke...

[@tamirbahar]

Thanks for the video! Now I'm eagerly awaiting the 5.8 release

[@Typed-Rocks]

Me too. Glad you like it :)

[@TheCoonHouse]

Not sure if I understand this. Why wouldn't you create separate types for "PersonType" and "CompanyType"? What's the benefit of doing it this way?

[@Betadesk]

Just to flex some TypeScript magic

[@Typed-Rocks]

I wanted to use a similar example as in the pull request where it was merged to make it easier for the reader of the pr to understand.

[@TheCoonHouse]

@@Typed-Rocks Could you give an example of where this would be useful? Always willing to learn.

[@rajikkali]

Yeah, looks like bad coding practice to me too

[@benny123tw]

Well explain!

[@LostZenith_]

I don't know about write less code, but it's definately a lot more readable. Excellent change indeed!

[@Typed-Rocks]

Absolutely. The thing aber better readability is always a plus

[@arthurtweak3801]

Omg 🚀

[@EmilyK92345]

type UserType = { person: { firstname: string; lastname: string }; company: { name: string }; }; function mockUser(type: T): UserType[T] { const mockData: { [K in keyof UserType]: UserType[K] } = { person: { firstname: "John", lastname: "Doe" }, company: { name: "Apple" }, }; return mockData[type]; } const personMock = mockUser("person"); const companyMock = mockUser("company"); compiled in 5.7 without overloads

[@gdgdgdgdgdgdgdgd]

works even without that mapped type annotation in const mockData

[@mikuhl]

This is not a great solution for performance sensitive applications.

[@Krmpfpks]

@@mikuhli doubt that it is slower in any JS runtime, they all will optimize that out.

[@eliuddyn]

Amazing 🔥🔥

[@Typed-Rocks]

Thanks 🔥

[@thechoephix]

Finally!

[@zeratax]

this was one of my biggest issues with typescript tbh

[@jon1867]

This is super nice!

[@Typed-Rocks]

Glad you like it!

[@pookiepats]

When your Linter gets a cool new feature

[@coder_one]

In all these years of commercial work, I have not missed this feature. What are its actual real world use cases (not so trivial like mocking data)?

[@Typed-Rocks]

Often it's for library authors. In a normal codebase you rarely need these advanced types. That's 100% true.

[@thejimmylin]

What is the nice // ^? feature from?

[@Typed-Rocks]

Its from a plugin called „twoslash-queries“

[@thejimmylin]

@@Typed-RocksThank you so much!😊

[@meuscc]

need partial type inference and pipe operator

[@Typed-Rocks]

Maybe in the future

[@moh6823]

You can just use keyof instead of overloading the function. It would result in the same code?

[@Typed-Rocks]

In the final one, this is true 👍. But we don‘t need that anymore with 5.8

[@darkerisbetter8699]

I’ve wanted this feature to narrow arrays. The overload style is gross (though I have used it).

[@Typed-Rocks]

I agree. The new approach is really nice and concise 🤘

[@ErnaSolbergXXX]

This just seems like one more way to create a messy code base with typescript.

[@giovanesouza8664]

JS devs got types and now they do this with them... Why?

[@taquanminhlong]

Good to see typescript being less dump 😂

[@SaurabhSrivastava-i1q]

I am not writing types which has become another programming language itself!

[@tesilab994]

How very strange to illustrate this example with a "UserType" which isn't really a type, but just a holder for unrelated types each with its own property name. The example would be better if your property names were capitalized, and each one independently defined as a type, and then you combined them into so a union.

[@zohnannor]

bro, please, increase the bitrate when exporting/recording the video. your videos are great, but all those artifacts ruin the experience!

[@Typed-Rocks]

Interesting. Are you watching it on a pc? I‘m exporting it with h.264 from final cut as mp4. Sometimes KZbin does scale it down :(

[@zohnannor]

@@Typed-Rocks yeah, I'm on pc, watching in 1080p. I constantly see those "flashing rectangles" of artifacts, and the edge of the circle of your webcam is very blurry hard to see :( I don't really know how to describe the artifacts lol

[@pantherofsteel]

Being so much excited for TS is one of the saddest things that I saw on internet today.

[@Typed-Rocks]

Then you must have an awesome curated internet feed 🤘

[@cenkakay3506]

yeah switch case really messy

[@dzienisz]

TypeScript is the most complicated thing in JS world. I just personally hate it.

[@Typed-Rocks]

Sad to hear. But I can understand

[@Betadesk]

Yeah I believe the type system is Turing complete lmao, but just cause it can be complicated doesnt mean it has to be. For example you could easily just make a mockPerson() and mockCompany() function whose types are straightforward

[@coder_one]

@dzienisz perhaps jsDoc?

[@hugodsa89]

Dude instead of overloading you could do an XOR

[@LordErnie]

Although I love TypeScript, these are the moments where I think its just still lacking. Really with all of the different ways we can use typing in TypeScript I'd imagine this would be a base feature in the first place.

[@Typed-Rocks]

I was also expecting that but the language is always evolving.

[@ShinSpiegel]

Unpopular opinion, the new code look uglier.

[@Typed-Rocks]

Maybe for this simple case. But if you have more cases, the overloading would be quite repetitive. But everyone to their likings

[@ShinSpiegel]

@ repetitive, yes. But also expressive. It shows what expect, generics on this level makes the code “unpredictable” since it depends on other types (that can or cannot exist closer) to the function. Either way, it was already a unpopular opinion.

[@userasd360]

type UserType = { person: { firstName: string; lastName: string }; company: { name: string }; }; function mockUser(type: T): UserType[T] { switch (type) { case "person": return { firstName: "John", lastName: "Doe" } as UserType[T]; case "company": return { name: "ACME" } as UserType[T]; default: return undefined as unknown as UserType[T]; } } Just for the return type to match each return is forcefully type casted to that return type or need to create overloaded functions for the same as suggested by you.

[@Typed-Rocks]

Also a great way👍

[@airman122469]

Until TypeScript has strict TYPES, I really couldn’t give less of a shit about its other features.

[@Typed-Rocks]

I don‘t think we will ever have this :(