It's been ages, but I swear that sometime in 2017 or so, @danr.bsky.social (TS team) told me "Use interfaces, not types, for objects". I've also seen people whom I trust less tell everyone to "use types, not interfaces". What is everyone doing now? cc @mattpocock.com - ThreadSky

benlesh.bsky.social • 193 days ago

It's been ages, but I swear that sometime in 2017 or so, @danr.bsky.social (TS team) told me "Use interfaces, not types, for objects". I've also seen people whom I trust less tell everyone to "use types, not interfaces".

What is everyone doing now? cc @mattpocock.com

Comments

runspired.com•193 days ago

Types unless you have a good reason for an interface. Interfaces being open reduce their performance and make them useless in editors for both typeahead and inline documentation.

runspired.com•193 days ago

I’ve never understood what the “interfaces are faster” crowd is doing wrong, feels like every perf issue or crazy TS bug I’ve dealt with has come back to having used an interface instead of a type.

runspired.com•193 days ago

Also discriminating unions are almost always worth it for the DX. Especially if you need to be able to narrow inside an overloaded function or method

runspired.com•193 days ago

The implicit index signature also makes them way more composable. Fewer rough edges for compatible but not exact signatures

cliff76.bsky.social•193 days ago

I'd err on types, but that's just me. Types are more flexible and can define primitives, intersections, unions, and tuples and can be used with literal value constraints.

jacobmgevans.bsky.social•193 days ago

Types because they can be computed, whereas interfaces are more performant because they are static objects basically

nickmccurdy.com•193 days ago

For performance and extensibility reasons, I recommend interfaces.

malindu.dev•193 days ago

How come interfaces are faster than types?

benlesh.bsky.social•193 days ago

I think it's less of a burden on the TypeScript compiler to reason about interfaces than it is to deal with the complications around & and | types.

But that's honestly just my rudimentary understanding of it.

nickmccurdy.com•193 days ago

To be fair they have made significant performance improvements to how types get cached, but I'm not sure it's reached performance parity with interfaces yet.

lancejeffers.bsky.social•193 days ago

That's largely it. Type unions with `& otherType` can easily lead to slowness in the compiler so are generally something to avoid. In contrast, interfaces basically do everything you'd want from a Type but can still be extended without the perf hit

natespilman.com•193 days ago

Also aren't types transpiled into classes, where as interfaces aren't converted into JS at all?

forivall.com•193 days ago

No, neither show up in js

samalrasmussen.bsky.social•193 days ago

https://github.com/microsoft/TypeScript/wiki/Performance#preferring-interfaces-over-intersections

cathalmacdonnacha.com•193 days ago

Matt says: "You should use types by default until you need a specific feature of interfaces, like 'extends'."

https://www.totaltypescript.com/type-vs-interface-which-should-you-use

astahmer.dev•193 days ago

I usually go with interfaces by default unless I need types (dynamic keys etc)

forivall.com•193 days ago

Interfaces. I'm almost always preferring interfaces

forivall.com•193 days ago

In addition to performance, https://bsky.app/profile/nickmccurdy.com/post/3lbatp2zvik2z , I find that they have better dev experience, at least for my preferences. Lmk if anyone has other preferences!

mattpocock.com•193 days ago

The question is not types vs interfaces, but interface extends vs intersections.

If you're choosing between those, interface extends is pretty much always better. type vs interface is basically moot.

nicolas.dubien.me•193 days ago

So sad that `type` still implies a performance penalty. I find the keyword way better to express functional types without OOP in mind. The interface carries too much of OOP and inheritance IMO. If only they were closer performance-wise 😔

bohlenlabs.com•193 days ago

Are we really worrying about this tiny bit of compiler performance? Let’s be clear: it’s not relevant at runtime!

benlesh.bsky.social•193 days ago

Scale is a thing for some of us.

mattpocock.com•193 days ago

It doesn't. '&' does.

l422y.com•193 days ago

interfaces for transmitted/external/parsed data, types for data that doesn't leave the application or needs enhanced typing

jamie.build•193 days ago

Only semi-related, but a common difference I see between real world usage of interfaces vs type aliases

Always prefer to use properties with function types, not methods

Methods are bivariant even with --strictFunctionTypes

https://www.typescriptlang.org/play/?target=9&jsx=4#code/PTAEGUEMFsFNQGYHsBOoBGSAuALUBLAOy1hQUgGNYBnUSQgE1CwE8AHeSAG30mpoBQREmUrwAogA8YbLvADeA0KDi4kDABRE2AVywAuUIR3R0pUAB8jOrlwCUhgG5J8DJaDYokbQ1sK6Da1NzK2NbO1AAXgA+UGdXAQBfAQEQUAA5bFhDABUcfFoCo2xQCiRoNkgsfHQ5UAB3fFxmHHgEHUIKaqRCZnYaOkxHWAF2zu7ewh70my5IWtg-AMNjYJQIxWU0gCUO6rhQUi80fAQG+ErqQt6AAzCuG-cywmokOQA6LiQAcyW9d6wSAACihYBQCvgeho7HYkik5FhDtIKnJDFIZHVIqBNqA0gAhbB4JBnXA0eDUHBIGxMMyHFDHajuVSUhgraazeZyAA0uLAAElOqhQV13J5vGzCDNbJzYDy0gBhIVgrBJIA

statisticsftw.bsky.social•193 days ago

Wow, why is prop allowed for method? That is obviously wrong.

jamie.build•193 days ago

In what way (that TypeScript actually models)?

statisticsftw.bsky.social•193 days ago

Oops I meant why is nonNullable allowed for method 😅

nicolas.dubien.me•193 days ago

I personally prefer types over interfaces. Interfaces carry an OOP philosophy with them, types look more functional conceptually speaking. That said for performance reasons, I should prefer interfaces 😅

likeafunnername.bsky.social•193 days ago

I don't prefer one over the other. But I guess I am curious if there are actual benefits in TS performance in certain scenarios.

reinhold.is•193 days ago

There's always a blog post.

https://www.totaltypescript.com/type-vs-interface-which-should-you-use

a11ymel.bsky.social•193 days ago

I use interfaces.

alanscodelog.bsky.social•193 days ago

Writing libraries I prefer types unless it's okay for the end user to extend the type, in which case I use interfaces since they can support interface merging. And if I expect the user to extend the type I use a Register pattern for more flexibility (pattern stolen from lucia auth).

samalrasmussen.bsky.social•193 days ago

If performance is your top concern the interfaces:
https://github.com/microsoft/TypeScript/wiki/Performance#preferring-interfaces-over-intersections

Matt Pocock comes to the conclusion that type is simpler to reason about for the most part though:
https://www.totaltypescript.com/type-vs-interface-which-should-you-use#default-to-type-not-interface

benlesh.bsky.social•193 days ago

I actually disagree that they are easier to reason about. & isn’t always reader friendly, and I find that reopening an interface can be prevented with lint, and in 10+ years of using TS, even at massive scale, I’ve never seen an interface reopened accidentally

samalrasmussen.bsky.social•193 days ago

Yeah I've used ts since 2014 and never knew you could accidentally merge interfaces, because I just have never named two interfaces the same in the same file. Why would I even expect that to work?

likeafunnername.bsky.social•193 days ago

Cool, thanks for the links!

rokuyondev.bsky.social•193 days ago

📌

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