DEV Community

Cover image for Stop Using TypeScript Interfaces

Stop Using TypeScript Interfaces

Afzal Imdad on June 09, 2024

Why You Should Use Types Instead Join our Vibrant Discord Community for exclusive information and insightful discussions Types and In...
Collapse
 
fyodorio profile image
Fyodor

IMO the described criteria are not enough to say “stop using” 😅 I’d say, use interfaces for object-oriented code and types for more functional codebases. And as usual, consistency importance prevails over specific choice.

Collapse
 
papilocloud profile image
papilo-cloud

My thoughts though 😃

Collapse
 
raunor profile image
Ville Uksi

STOP posting STOP posts if you are not aware of the topics you're ranting about. Interfaces and types have clear distinction on use cases and both are essential for TS.

Collapse
 
wintersunset95 profile image
Winter

💯

Collapse
 
szeredaiakos profile image
szeredaiakos

NO!
Interfaces are interfaces and type definitions are type definitions. You should probably dig into the history of both before starting another "best practices" scam.

Collapse
 
bwca profile image
Volodymyr Yepishev

Alternatively one could stick to what TypeScript team recommends. Always type over interface seems like religious fundamentalism 💁

Collapse
 
zeeh1975 profile image
zeeh1975

"For the most part, you can choose based on personal preference, and TypeScript will tell you if it needs something to be the other kind of declaration. If you would like a heuristic, use interface until you need to use features from type."

Collapse
 
wintersunset95 profile image
Winter

STOP using CLICKBAIT titles

Collapse
 
matthewjheaney profile image
Matthew Heaney

The argument that you should stop using interfaces because of declaration merging is completely bogus, since use of this typescript feature is extremely rare, and it's doubtful more than a few typescript programmers even know about it.

At Google we're required to use interfaces instead of types. If you do use a type, it gets flagged by the TS linter and the presubmit check would fail.

In practice types and interfaces are complimentary language features, and sometimes for advanced type manipulation, these features must be used in combination.

Collapse
 
bwca profile image
Volodymyr Yepishev

How do you handle generics that produce mapped types with mere interface if it's linter flagged? Do you just write new interface instead? 🤔

Collapse
 
matthewjheaney profile image
Matthew Heaney

The rule at Google is, don't use a type if you can use an interface. Of course this doesn't rule out all use of type-style declarations. Really, it just boils down to this:

type T = {n: number};
vs
interface I {n: number}

The latter is allowed, the former is not.

Collapse
 
afzalimdad9 profile image
Afzal Imdad

Subject: Apology for Posting Incomplete Blog Content

Dear Esteemed Blog Readers,

I hope this message finds you well. I am writing to extend my sincerest apologies for the recent oversight regarding the incomplete documentation in the blog post I shared with you all. It was an error on my part to neglect thorough verification before posting, and I deeply regret any inconvenience or confusion it may have caused.

I understand the importance of providing accurate and comprehensive information to our readers, and I take full responsibility for falling short of this standard. Please know that this oversight does not reflect the values or commitment of our blog team.

I want to assure you that I am taking immediate steps to rectify this situation. I will diligently review the complete documentation and replace the incomplete content with accurate and detailed information within the next few days.

Your trust and engagement are of utmost importance to me, and I am dedicated to ensuring that our blog maintains the highest quality standards. Your understanding and patience during this time are greatly appreciated.

If you have any further questions or concerns, please do not hesitate to reach out to me directly. Thank you for your continued support and readership.

Warm regards,

Afzal Imdad

Collapse
 
pwnorris profile image
Pwn Norris • Edited

Imagine being a "Person" but also being "Work"...
You'll soon be a "Person" implementing "Unemployed" if your employer sees this post!

Correction: According to my wife, I am indeed, a piece of "Work"...

Collapse
 
chobotx profile image
ChobotX • Edited

I found out that the best for our team is to use types for data and interfaces for function parameters and vue component props.. This way we achieve both dependency inversion and interface segregation in our vue/ts cosebase.

eg.:

type Person = {
    name: string;
    surname: string;
    age: number;
};

interface Named {
    name: string;
    surname: string;
}

const getFullName = (input: Named): string => {
    return input.name + ‘ ‘ + input.surname;
};
Enter fullscreen mode Exit fullscreen mode

Function doesn’t and shouldn’t need to know anything about age.

The difference for us is simple. Type is always complete, interface might and probably is only partial.

Collapse
 
jackd5011 profile image
Jack Davenport

That last line isn’t necessarily true. Types and interfaces both have support for optional parameters, and obviously at runtime it’s possible for any of the parameters to be undefined.

All you’re doing is inexplicitly creating an extended interface/intersection type.

Collapse
 
chobotx profile image
ChobotX

I might missunderstood you, but my example is exactly the opposite I think.

It’s not about extending ‘Named’ with ‘age’ yet about ommiting ‘age’ from ‘Person’ without any direct dependency on it. So you can use ‘getFullName’ for types ‘Person’, ‘Cat’ or even a ‘Car’ as long as it satisfies ‘Named’ interface 🤔

Sure you can take it the other way and make your data be an intersection type of the component/function types it’s used at, but then there is no segregation..

Am I missing something?

Collapse
 
mattpocockuk profile image
Matt Pocock

Thanks for the shout-out, but there is a lot that's incorrect in this article.

Classes can implement types.
Interface extensions are significantly faster for tsc to parse than intersections. Types and interfaces are the same, but the way you extend them matters.
There is no 'order of precedence' with declaration merging.

I still agree that types are preferred until you need a feature of interfaces, but I don't think this article has enough fact in it to be used as a reference.

Collapse
 
jackd5011 profile image
Jack Davenport

Hello Matt 👏

Collapse
 
jason_espin profile image
Jason Espin

Please do not write clickbait articles like this when you do not know what you are talking about. It is misleading for junior developers who do not know any better. To anyone reading the comments, ignore this article and instead follow the guidelines laid out by the Typescript team.

Collapse
 
digitalhallucinations profile image
DigitalHallucinations

Damn you got shut down… and rightly so

Collapse
 
yutakusuno profile image
Yuta Kusuno • Edited

Especially, in large code bases, the performance of the interface is better than that of the type in some cases.
github.com/microsoft/TypeScript/wi...

Collapse
 
zero_001 profile image
zero

Your exemple : Person extends Job is so wrong and kinda anti clean code...
You don't tell a person has a job by doing that, actually you create Interface Person and Interface Job,
You then create a class to represent a person with a job(extends Person, extends Job)
That's a basic concept of Object oriented programming present in many programming languages.

Collapse
 
marcus-sa profile image
Marcus S. Abildskov

Tell me you know nothing about TypeScript without telling me you know nothing about TypeScript.

Interfaces are strict, types are not.

Collapse
 
iamfoxx profile image
jerry Almeida

I appreciate your efforts, but No thanks!

Collapse
 
jackd5011 profile image
Jack Davenport

Tbh I feel like article does a better job of convincing you why you should use interfaces rather than shouldn’t.

The main drawback seems to be declaration merging and while that could cause issues, it’s pretty unlikely to happen in a well managed codebase, so I don’t think the argument is really strong enough.

For my projects I use interfaces primarily for defining object shapes, and then types for creating union types or extending existing types from libraries. They both have valid uses in most Typescript codebases.

Collapse
 
motss profile image
Rong Sen Ng

Come work with me and I'll force you to use interface by default.

Collapse
 
emwadde profile image
emwadde

The title sounded clickbait, so i came for the comments to actually learn something.

Collapse
 
mafi020 profile image
Mahfuz Ahamed

As both does almost the same, one should stick to what they are comfortable with.

Collapse
 
ankit_saiyan profile image
Ankit Saiyan

Not informative at all or should I say it's misleading... It didn't give away any useful fact to prove we should not use Interfaces... Click Bait!

Collapse
 
harlyon profile image
Harrison Ekpobimi

Hmm your opinions. But I don’t think it’s a valid reason to say one should stop

Collapse
 
abdul_rauf_baf9f0f265dd39 profile image
Abdul Rauf

You didn't even justify the title of your artical. Please be carefully to select a title and stop wasting time of others.