Why use Type and not Interface in TypeScript
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- Опубліковано 10 чер 2024
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⏱️ Timestamps:
0:00 Type Alias vs Interface
2:05 Interface problem 1
3:15 Interface problem 2
4:05 Interface problem 3
5:39 Interface problem 4
6:49 Consideration
7:34 Interface problem 5
9:41 Interface problem 6
11:49 Classes
12:33 Best arguments!
12:47 Arguments pro interface
#typescript #typescripttutorial
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TypeScript, not InterfaceScript
Hahaha
Cool!!man
hahaha nice!
that line made me like and subscribe
😮😮😂😂😅
My rule of thumb is use interface until type is needed. 90% of the times I find myself defining objects
Samezies. Best of both worlds
For sure to me it all looked like code smells taking the idea of DRY too far adding more complexity then the problems they solve, or maybe a smarter way of being lazy, just write a few more lines of code and don't create un-nessisary coupling
yeah, i think it doesn't matter that much between type and interface
True. Same for me. Having type in all places over interfaces is bit fancy in TS though 😅
For me its just more natural to define interface for a component rather than its type. That interface can have typed members in it self. Interface is like a contract while type defines ... well type :)
I use interface for objects (which is mostly what I do when defining data models) and type for all else as needed. I don't think they're mutually exclusive. Use them both.
I've heard about following one pattern is a good practice. That means if your project uses interfaces it is right to use only interfaces and vise versa
Me too. I prefer not using equal sign if i can
They may do similar things but the concept they convey is different. I use interface as the meaning of the interface that there is in Java/C# or other OOP languages, that is something a class needs to implement. While type is like a struct/record, something that is only used to pass around data, not methods.
This way in my opinion the codebase is clear, since you have a separation between two concepts.
I agree with this. You don't have to exclusively use one or the other. The bad use case examples for interfaces in this video are a result of misusing interfaces IMO.
This is the way
There’s no material distinction between those two, especially in a language with function types. Maybe it’s the functional programmer in me speaking, but I try to break the boundaries between those two things and stick to the one thing that can represent EVERYTHING.
However, I do understand the benefit of providing something that’s clear and similar to the code that my teammates have worked with in other languages.
Just my personal preference…
@@rafaelkhan_ I agree there is no difference. However I tend to use "type" for records or structs, and interface for defining the methods that an object exposes. For example, in the Rust language, type would be the struct, and interface the trait.
I disagree. Interfaces has limited functions for a reason. It makes it clearer to understand what the code is intended for at first glimpse. Having lack of features is an advantage in this case when it comes to readability.
I'm afraid that junior developers will now haphazardly add 'type' to their code after watching this video.
Examples of where using type is going to break the world?
I don't really consider these to be problems... I consider them different use cases. Type I use when aliasing.. Interfaces I use when defining an interface. Call it semantics - because it mostly is. I actually consider the fact that interfaces only define object shapes to be a benefit, it's generally pretty rare that I want to simply alias an underlying / primitive type other than as a placeholder when passing it around. Quite often I'd alias a string as EmailAddress for example but usually because I'm passing the type around and at some point I suspect I may want to replace that type alias with a proper interface without replacing all the areas where the type is passed (of course you have to change the places that actually operate on the type).
It's far more common that I want to define a contract for an object so I'm happy using interfaces as that's what they are. I also actually prefer the syntax as it conveys more info (seems more expressive) saying "interface IDerivedThing extends IBaseThing {...}" rather than "type IDerivedThing = IBaseThing & {...}".
Wrote this reply in another reply thread, but essentially it's to answer some people who complain to just use interfaces until you can't. I create an example hypothetical scenario to showcase why this is unnecessary in this reply:
I favor always using types just like Wesley explains in this video, because essentially it keeps everything consistent. If you really have the specific case for more complex interface polymorphism, e.g. complex hybrid types, then you will already know you should use interfaces and create that exception. If not, every other case you can use types and make it consistent.
To say you use interfaces until type is needed is like saying, if we bridge the example to declaring variables, that when you define an object u do:
const obj = { example: 'example string' }
and when you "know" you need to not use an object you just use another way of declaring:
dec loggedIn = false
In this situation, "dec" is a made-up replacement for const / let that stands for "declare variable", where you know you are declaring a variable that is not an object. This is the same as the interface type situation, but if you can do:
dec obj = { example: 'example string' }
why would u keep switching between dec and const... just use dec all the time.
Now back to the video, it's the same with types and objects. If I need a union I use type = type1 | type2 | type3 etc or some type like type = AnotherType[] or type = typeof keyof Anothertype, and if I needed to type an object I have to suddenly swap to interface or vice versa it's just messy. Just always use types, just like you can always use const, even if they add a new keyword to declare variables with objects to allow you to do very specific things that aren't needed often you would still continue to use const to declare both objects and other stuff.
Interface is for shapes in the form of objects, you can "extend" a shape. With shapes you can build a hierarchy.
Type alias is for type composition. you can compose types from simple types. A type is a fixed definition. You can change/omit properties with the help of utility types.
That's because interfaces are... well, interfaces. They represent a contract - a set of methods and properties exposed by the object. They are not types. If types were only for primitives, interfaces would make much more sense in TS.
Btw, you can create an interface for a primitive too like this: interface Address extends InstanceType {}; It is just not as convenient as with types :)
his point is that using type is just much more cleaner
One point in favor of interface is that it can extends from both type alias and interface. A type alias can extends (intersects) from types but cannot from interfaces. When working with third party libs that export props as interfaces, this might be an issue if you strictly use type alias in your project
Hmm. Didn't get you. You can do like this: `type User = IGuest & { createdAt: Date }`
@BlueCell
interface A{}
interface B extends A{} //works
type A = {}
interface B extends A{} //works
type A = {}
type B = A & {} //works
interface A {}
type B = A & {} //breaks
@tiagoc9754 you are not right. Maybe it's old version of ts? For me it works. Just tried
@@BlueCell it might be the case. I haven't tested on new versions as it never worked before
this should now work in the recent versions of TS. Maybe you mean TS interface overriding.
Funny thing is that this video convinced me to use interface over type unless necessary :)
As a person who new on this typescript world, your video is really understandable. Thank you.
i prefer interfaces honestly because they feel more strict and the extend keyword feels more clean and i find the most complex features of types not really necessary. And ofc interfaces are a concept that exists in other languages. I only use type when i need the union feature. In my company I work on a massive react project with ts and most devs prefer interfaces it gets the work done.
you can use ampersand in types, it's like an extend but can do more.
I'm going with interface always, type for everything else interface can't. So I have a nice distinction without any confusion.
This knowledge is extremely useful when you're fixing someone else's code. You would understand the working 'intent' more clearly (or quicker) knowing the utility and restrictions of each facility. Thanks for the review & lesson.
what plugin do you use for this autocomplition?
While it might be debatable what to use, but this is the first time I understood the difference between interface and type. Thanks for that!
What do you think about creating DTOs interfaces? I know we can use "Omit" to filter a field but what if someone forgets about that and sends back the entire model to the client.
I would absolutely love a series of videos on how to get started with TypeScript, specifically the main places where TypeScript needs to be written in an app, where it doesn't, and all the necessary syntax.
Just finishing editing this exact video. Stay tuned :)
What do you mean where ? Everywhere !
What adson do you have installed to give you completion suggestions?
there is one thing interface absolutely crush type, that is when building higher kinded type, an interface that can accept another utility type as argument
Hmm would you mind giving an example?
@@ByteGradI assume he means generics. And yes, that is something that is extremely useful.
Which extension makes the object's properties suggestion when creating an object?
I still prefer interfaces for simple object shapes or anything that contains a function, so it can be used to implement into a class instance. Types for anything more complicated when dealing with plain objects. That's my rule.
I must say I was skeptical, but that was quite convincing 🤔
It's "Typescript" not "Interfacescript" I like this a lot 😂😂😂, by the way, this is one of the best videos about a comparison between Types alias and Interface in Typescript, thank you!
One uses interfaces if they wish to flip the dependencies of a system around, mainly in OO environments like C++, C#, and Java. Javascript has the rule of composition over definition;Javascript follows structural comparison rules and doesn't really care about structural definition comparisons (is it of the same direct type or is it a child of one).
Because objects in js follow different rules for substitution, interfaces aren't really as needed in the same way they are needed in the earlier mentioned environments. In js, expecting an object of a type with a function validate means it can be any object as long as their validate matches the expected function header (and even that doesn't have to be true).
Typescript interfaces are a bit weird. They are nice, but types are indeed a better alternative.
I loved the "Type"Script pun.
The reason I use Interfaces instead of Types is because when skimming through code Types can confuse me with regular variable assignments.
But I totally agree with the video. I wished that maybe something more in between where types don't look like too much like regular code assignment but it would be as flexible as types and less verbose compare to interfaces.
good comment
Thank you so much for your video, I just started learning typescript and it's a bit confusing at first, but I'm getting the hang of it
This video is a great refresher of TS!
In the example where you extract a type from a const, how would you specify a property as having a union type?
I use interface for initiating a generic class blueprint (interface has some methods that class needs to implement). Can Types also be used to define as containing functions ? sorry for the basic question.
As someone just starting out in typescript you may have sold me on using type > interface
came for the info - subbed for the voice
A bit skeptical at first but this makes sense! Thank you for sharing.
Thanks for the great insight and your explanation ByteGrad !
However, I wanted to ask. You mention that type aliases has some advantages over interfaces, but why do you then arrive at the conclusion to favor Type aliases pretty much always over interfaces, and not interfaces for objects, and type aliases for all else for example?
Also, I believe I had read that interfaces is a bit lighter on the tsc compiler lol, not that it matters much in terms of dev experience.
What theme are you using? @ByteGrad
The last argument pretty much makes the biggest point in favour of using 'interface', i.e. getting better error messages. When you're dealing with TypeScript and complex types that can often float around in libraries and codebases, you need all the help you can get from error messages.
This is a misleading title! Types are not a silver bullet and there are plethora of articles out there explaining it better than I could ever do. As with everything, use the right tool for right problem! It is that simple. I mean, there is even an eslint rule (called "prefer-interface") that is part of the "recomended" config that suggests you to use interface where possible.
I used class for Dtos , not sure type is better ? (I am from c# developer)
Super, always looking to understand when to decide between these two
One of the best of your videos which I watched. But still many to watch. Great job. Thanks.
very concise and clear examples. great!
The problem with keyword `type` is that first two letters t and y are the most hard to reach on the keyboard... the finger needs most stretch :) ... that's why I'm constantly using interfaces for object types as after two letter the completion gives me full word
Interfaces have advantage where we want to implement Dependency injection, can we do that with types?
Omg, So many typescript tricks that I dont know, love it
What a great video! I understand now many things what’ve not understood before! Thanks dude!
Don’t use extends unless you absolutely have to because when managing a large production codebase you may eventually get stuck in a web of dependencies. Nothing is worse than sorting through a tangled web when you have a pressing deadline. Keep everything as independent and modular as possible, even if it adds a bit more boilerplate, because it will save you time in the long run.
agreed!!
Thanks I never used types this way
agree, for me interface required only if you develop some library, just because of merge availability
Very Interesting !
I believe we can also use Pick keyword to assign part of a type
I recommend using interface when dealing with objects as it provides faster performance and provides more info in code hints. If there's a need for a feature that exists only in types, then use types.
"It's called 'Type'Script, not 'Interface'Script." ROFL Touche... Good point...
Can you please tell us which all extensions you use ? Specifically for the intellisense. Thanks!!🙏🏼
Its actually GitHub Copilot
Most of these "problems" assume that interfaces and types are exclusive, which they are not! Just because you decide to prefer interfaces to define your objects doesn't mean that you must limit yourself and not use types to solve all those use cases. Only problem 6 really touches on a "problem" of interfaces, everything else was never something interfaces were meant to solve. Interfaces are meant for objects, and types can do objects too, a far more interesting video topic would be to ask "for objects, should I use interfaces or types?". Aside from problem 6 (which is mostly solvable by avoiding global types which is a bad practice anyway imo), this video doesn't really provide any arguments for one or the other.
Thanks, it was very helpful. Just a comment the Typescript's interfaces seems to follow the Open-Closed Principle. And that is very helpfull when you want to extend the behavior without modifying the interface
Good examples for good usages of type. My pattern is to use interfaces to describe behaviour and types for state.
The thing with "open interfaces" is really crap in typescript. especially when you see an interface a contract.
agree. I'm getting tired to see class defined in Typescript project: keep passing arguments to create instances do the same job, or use to create one instance only to handle a single work , instead of write curry functions. 2023 and people still stick with OOP in JS/TS development.
thanks didn't know all differences. I always use type everywhere, interface when I need it which is very weird unless when Im working with other devs
I use type all the time. I can use type for anything related to type which TS needs. Typing "type" for me is faster, saving some keystrokes.
Really appreciate your content man, very useful!
omiting something from interface, you probably did it wrong
you can make the name optional property indicates that its can be null or undefined, but still there
or just split the interface coz its reflecting types of different concern
I figure this out on my first day with TS.
I'd argue that there is literally no point in defining a type alias for a primitive.
Try out an FP language like OCaml, then we can argue.
Interface is an OOPs way of defining types, type is a functional construct and aliasing is common in functional land. You get to define complex types in a terse wayand aliasing gives self documentation.
The way he showed type alias in the video doesnt add too much value, but there are useful cases of aliasing
The TS compiler is more performant when extending interfaces vs. intersecting types. Usually no visual difference until you're doing something complicated and have to create a type that intersects 50-200 different object types.
But if that's the case you should probably figure out why you feel the need to do so and refactor the runtime code to be more TS friendly
do you have any source about performance? its new info for me :) i cannot find serious source of info even compiler itself! :D )
That doesn’t affect the production build though, right? Like, only in dev or when deploying, but the end user won’t get a performance hit because it’s already compiled.
"more performant when extending interfaces" - may be that's why the TypeScript docs in fact recommend using interfaces over types
Well explained! I love the TypeScript not IntefaceScript part 😂
This was very helpful, thank you!
Most arguments in the video and comments are mostly subjective code style. Many feel it's more natural to write interface to reason with their architecture like they did in Java and C# - I WAS in this camp and defaulted to interfaces, only using types when needed. However, there is a very frustrating error message that made me default to types:
Typescript: No index signature with a parameter of type 'string' was found on type '{ "A": string; }
Since interfaces can be extended, the TypeScript team doesn't consider it safe to infer the index signature even if you provide a subset of the type (the type in question very clearly only has string indexes, so you'd except TS to naturally accept this). You often encounter this when you use generics -> POV: you made a nice generic component that should handle anything derived from your base type and when you use it TS slaps you with that error that makes no sense at first (and to me just seems like a bug!)
There are two workarounds:
1) de-structuring the object before you pass it -> this is ugly and feels like a hack
2) use a type instead of an interface and inferring index signature simply works as you'd expect it
Can you tell your extensions please? This auto complete of yours seems perfect! Also great video.btw
Copilot
However, something useful about interfaces, is that you can define an interface of the same name multiple times, and they will all be merged together. This is super nice for things like adding a function onto a builtin class like Array, String, Object, etc.
I'd rather have a new type that explicitly has new behaviour rather than overriding built-in types. Sounds like it'd become hard to follow for new engineers to a codebase.
You probably shouldn't extend built-ins, but write additional behavior in a reusable function.
@@HackersRUs how would you do that if said type comes from a library? With interfaces it is very easy and straight forward, but with types you would have to copy everything from the type manualy and than add new props
Don't pollute prototypes. Bad juju
This is the exact reason why interfaces are bad
Btw, you forgot to mention at 5:43 that you can also give label names to tuples, found that very handy especially when separating a function paramaters into a separate type and then spreading them out 😁
that info of double Interface declaration causing merge is helpful!
but i will still use interfaces for the sorter error message highlighting
Thanks for the video, great explanation!
don't know how it works in typescript, but for other languages I use Interface when I should describe an object with methods, but don't want to code methods, because they will be in a different project. so my current project needs to know how to use these objects and compile without knowing and compiling interfaces code.
to me interface and class were designed for people from OOP language (Java, .Net., python, Ruby, C...) switch to JS.
So, I use type over all interface, because I don't want to see any classes in my Typescript project : Composition over Inheritance :).
Having an OOP background, imho "interface" is completely wrong in TypeScript. An interface should describe a way to communicate with other parts via methods by defining their signatures.
I agree on the type is the better choice for all your examples, not because something may be ugly to write, but because it simply is wrong to me to define properties on an interface. For me, that's actually the line a draw: Types defines data structures. Interfaces define ways to communicate throughout the system.
So interface for objects and types for literally everything else?, very nice to know, thanks!
And type can define objects as well
I've had discussions about this before but never took the time to look into it properly. You've sold me with just the interface problem 1! Great video, subbed. :)
Interface Problem 2 is the exact reason I DON'T use Types... saying this could be an array or a string means any consumer of that data has to account for both. A type should be a single, immutable thing.
Thanks a ton, this cleared lots of concepts...🙏
It mostly comes down to coding conventions. We eventually desided to use interfaces for props and types for individualy typings.
Great video, I'm so glad that UA-cam recommended your channel, I found myself doing a lot of mistakes that you explain in your videos and they improved my skills. Thanks!
I disagree:
I use both type & interface and as you shared in the docs, the benefit of interface is the extensibility, so you can reuse the same interface & extend it to be used in other places.Thats a big plus with complex code base where you have types manipulation to be reused in different areas of the app.
You can just use types for any of the situations you mentioned, the whole point of the video is that interfaces are the wrong primitive to use.
You gonna use one when you need one, but most of the time you don't need a interface. even in large codebases.
"&": Am I a joke to you
@@Enderman0000it’s like people don’t watch the video, right?… 🤦🏻♂️
Great videos!
Very helpful, thanks :)
Thanks Bro, you're great dev, my respect
Thanks, appreciate it
Why not interface for object and type for everything else ?
basically if you come from a classic OOP language (not JS) you probably knew all these things
Been meaning to find a difference or reason to settle for one or the other. Thanks for a ton of great points - I am convinced.
I stand the position that if you define types for object，you should use type，if you want to describe profile of a class，you should use interface，and implemented by class，all in all，interface used by class，and type for simple object
The hammer's problem is that it can't look at small objects; it can only drive nails, and that's its PROBLEM. On the other hand, a microscope is quite versatile. It can drive nails and examine small items. So, choose a microscope.
Your voice is so smooth sounding, such a pleasure listening to you teach. Great video!
Thank you
Interfaces aims to define contract and provide definitions to the classes. The interfaces and types may look same and let you exhcnage. However, both types and interfaces have different meanings and hence different use cases!
When you say "ugly" to me it seems that is more descriptive wich is better. So for me most of the strong points in favor of Types ate actually not pros but cons. Nonetheless its a great video explaining the differences between Types and Interfaces.
I use both in most cases. Interface mostly
Thanks for the video. You convinced me that the type is much more useful than the interface! Like
please can you post the file you was writing in I reallly like the comments there
Interfaces for behaviour, type aliases for data.
I have finally understood this concept. 😋
such an amazing video, keep rocking dude!
Interfaces often compile faster than types because of their different scope
I agree with your thought process. Damn I need to go and create one giant PR replacing interface to type now :D. Maybe add a lint rule to block interfaces :D ?
I wonder why Microsoft created interface in the first place now.