Declaring static methods in the interface should not affect the representation of the interface in JavaScript code (it is not present). Second method workStartedhas implementation and it is not an abstract method. Holding off on this until we hear more feedback on it. From a practical point of view, the interface is a kind of specification - a certain set of methods that are mandatory for their implementation in a class that implements this interface. Since you were considering this issue, could you please share your ideas about this? For example: For example: class Employee { private static headcount: number = 0 ; constructor ( private firstName: string , private lastName: string , private jobTitle: string ) { Employee.headcount++; } public static getHeadcount() { return Employee.headcount; } } Thus, we could get the following: This way, interfaces could keep their meaning, and class_interface would be a new kind of abstraction symbol dedicated for classes definitions. I think it is a little sketchy to add static methods to interfaces because an interface should define an object, not a class. Have a question about this project? Now that we can seamlessly mix static methods into our class definitions, it's certainly worth taking another look at when we should be using static methods in our TypeScript / Angular 2 classes. I want to be able to. I don't think there's an existing constraint for that, is there? Instead, the list instance ends up exposing the instance type directly, which is not relevant to the list instance itself and should be accessed through the constructor. Let's pick up the discussion at #34516 and #33892 depending on which feature you're going for. It's so ugly to write workarounds because of this feature is yet to be implemented =(. Explore common practices, the compiler, classes, ES6/7, functions, and everything else you need to unleash your inner TypeScript desire. I may be completely wrong here as I am not very familiar with the internals of the TypeScript engine, this just seems to be the case from experimenting within VSCode. This comprehensive course takes you on a journey through the TypeScript language, unveiling the many benefits of adopting static types. But in some cases I also need to acces this value when I only know that the accessing class is inherited from AbstractParentClass, but I don't know which specific child class I'm accessing. It also doesn't raise as many questions as this does. You add them to your program… And because of that, it becomes statically typed. I don't think I'm getting it. Great point, I honestly forgot that native ES6 classes don't have an abstract keyword. Static constructor in TypeScript. If this is explicitly annotated to something else by the user, we should still be safe because we shouldn't make initialize available on typeof Alpha, and only on Implemented. There are reasons why languages like C# don't have static members to interfaces as well. What @patryk-zielinski93 said. When compiling this code, an error occurs: 'static' modifier cannot appear on a type member. Technically if you write. Here's a rough sketch of "quasi-abstract" based on @minecrawler's suggestion that you can use today: Building on @minecrawler's suggestion with an Implemented utility type: Regarding the following snippet on an abstract class where .foo() is abstract: Should this error? Therefore I have these dummy implementations that just say "override me in a derived class if necessary". Inheritance of class/static methods can and does make sense, particularly for the static method factory pattern, which has been called out here by other posters several times. Would love this feature as well. This doesn't address the issue regarding import aliases with this model that you raised however. Successfully merging a pull request may close this issue. While unfortunately this does not throw errors on class declaration, it does guarantee that any function Foo that requires extra static methods is not callable on any defined class that does not define them. class extends MyAbstractClass), not when using it as a type (e.g. Thus, smart static type system with type inference capabilities would allow you to omit type annotations in thi… I'm using the @rsuter/nswag library, which generates swagger specifications. @thw0rted I think the best alternative for the createInstance and initialize case is just to be upfront about the requirements of the class on the createInstance function. The implementation of this feature in JavaScript should be similar to the implementation of interfaces, abstract methods and static methods. But for something simple like this, it doesn't really make sense, and only ends up in things being more complicated than they need to be (the subclass would need to extend the abstract class and implement some interface, makes naming things more complicated, etc). For anyone looking for a workaround, you can use this decorator: since we're calling through a type parameter, the actual base class with its hypothetical abstract static factory method will never be involved. Type Alias a primitive is not terribly useful, though it can be used for documentation. I feel as though static methods in interfaces is not as intuitive as having static abstract methods on abstract classes. @thw0rted Yeah but you have to work around a bit. What I'm not seeing in this discussion are cases where the implementation is invoked by way of the type of the base class as opposed to some synthesized type. It should be legal to have abstract static (static abstract?) Add support Interfaces to define static methods, JSDoc: params for typed function are inferred as any, Support 'static' to be used with 'abstract' and generic type, feat(auto-init): Convert JS to TypeScript, Activate strictBindCallApply and strictFunctionTypes compiler rules, Wrong Code Gen for Abstract Static Functions in Module, Allow specifying interface implements clauses for the static side of classes. #26398 (Type check static members based on implements type's constructor property) looks like a better solution... if something like this were to be implemented then I'd hope it's that one. It's a special kind of class that would only allow static members to exist - effectively boxing unsafe operations away. Like, if I could write, where Concrete uses conditional type math to be never if the generic argument is abstract. However, none of the above options provides this functionality in a safe way. It seems restricting abstract static implementation purely to the only one class which implements it might solve the problem. . The linked class serves as a common base class for them. The text was updated successfully, but these errors were encountered: Static interface methods generally don't make sense, see #13462. Statische Methoden sind mit dem this Schlüsselwort nicht direkt erreichbar von nicht statischen Methoden. (That's the other "child issue" of #14600, BTW.). https://www.reddit.com/r/typescript/comments/bcyt07/dynamically_creating_instance_of_subclass/, https://stackoverflow.com/questions/57402745/create-instance-inside-abstract-class-of-child-using-this, https://stackoverflow.com/questions/49809191/an-example-of-using-a-reference-to-an-abstract-type-in-typescript, https://stackoverflow.com/questions/53540944/t-extends-abstract-class-constructor, https://stackoverflow.com/questions/52358162/typescript-instance-of-an-abstract-class, https://stackoverflow.com/questions/53692161/dependency-injection-of-abstract-class-in-typescript, Suggestion: Add abstract static methods in classes and static methods in interfaces, https://github.com/AlCalzone/node-zwave-js/blob/d2e29322d0392e02b7d8e2d7c8c430cb8fcaa113/src/lib/commandclass/CommandClass.ts#L363, https://github.com/AlCalzone/node-zwave-js/blob/d2e29322d0392e02b7d8e2d7c8c430cb8fcaa113/src/lib/commandclass/CommandClass.ts#L368, Allow static members in abstract classes to reference type parameters, Find a more native way to augment the React Classes Typescript definitions, Investigate empty interfaces in TypeScript defintions, call non-abstract methods on the abstract class from outside the same class, call abstract methods from non-abstract methods inside the same class. And by the looks of it the thread about allowing static methods on interfaces is also stuck , Commenting for future update notifications. [...] actually crash on the line before the "Error" comment. Abstract classes are mainly for inheritance where other classes may derive from them. In above example, we have created an abstract class. keeping separate TypeScript types for the instance and the class)? I think I have to pass separate instance-type and class-type generic parameters, since I'm not hard-coding "YourClass" as in your example. Use the following procedure to create a program using a static method. Because of this limitation, the typings for React currently include two types: a Component class, and ComponentClass interface including the constructor function and static properties. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. The interface doesn't only define the functionality an object provides, it is also a kind of contract. If you share that opinion, you also say java and other popular langages make it wrong. In case it throws, the page does not get constructed, but rather the error page. TypeScript type vs interface are the important concepts of Typescript. That would likely fall under type-directed emit and therefore is a nonstarter. Similar implementation example // No error for failing to provide `static initialize() {`, WAT? For example from a network request. Do either of you have any comments about this feature, and would a PR be welcome? Static members are referenced by the class name. TypeScript - Abstract Class. Read the comments for more information on its limitations. We can explicitly type this and make sure the passed in class is a concrete class derived from A (ie has a callable constructor, that returns A) and has any extra needed static methods: While initialize is not an abstract static member of Foo, it acts like one for any client that calls createInstance. We’ll occasionally send you account related emails. No it does not because abstract has no effect at runtime--it's purely compile-time info. // works, because we expect `this` to be a child implementation, // ERROR: foo() does not exist on A (because it is directly abstract), // ERROR: bar() does not exist on A (because it is indirectly abstract), // not abstract anymore, so B.foo() exists, // WORKS, because B.foo() is not abstract, // N.B. Classes, methods, and fields in TypeScript may be abstract. ETA: of course if a keyword were added that means "and is not abstract" that would also be a good resolution. Or any workaround for constructors on abstract classes? https://stackoverflow.com/questions/52358162/typescript-instance-of-an-abstract-class. ... this doesn't seem to be valid syntax, am I missing something? I was really excited to use real abstract classes in a language after being in ruby/javascript for so long, only to end up dismayed by the implementation restrictions - The above example was just my first example of encountering it, though I can think of many other use cases where it would be useful. TypeScript’s abstract classes and methods solve this problem. Or am i wrong? to your account, This is a continuation of #14600 which had two separate features proposed in the same issue (static members in interfaces and abstract static class members), static abstract method property properties implement concrete. I decided to rewrite a small TypeScript+React+Jest side project into ReScript. This also would make it impossible for concrete static methods to invoke abstract static methods: On the one hand, this is good, because A.createInstance() definitely does crash. The types of the subclasses are related structurally when the type parameter is instantiated. So I don't see any logical reasons why class may have static method and interface doesn't. then foo isn't exactly the declaration of SomeStaticAbstractClass itself - it's an alias. You signed in with another tab or window. angular issue. :) If you carefully look at the program above, you’ll notice that in this case types can be determined from the context. Is the thing I'm trying to describe some kind of uncommon pattern, or an antipattern, or something? Of course, this is given to the access modifiers that are designated for the member. In Angular for AOT compiling, you can not call functions in decorators (like in @NgModule module decorator) Take this early example from White Label. Such is the case with static methods. // expected error, but got none: displayName should be a string, // expected error, but got none: defaultProps.name should be a string, // error: defaultProps.name should be a string. Both not possible yet. This is not evangelism of ReScript or a one-to-one comparison with TypeScript. I suspect many people are currently not using ComponentClass, unaware that their static properties are not being type checked. @RyanCavanaugh I see a possible option 5 where we could mimic the behavior of the existing abstract class. The setter method accepts a string as the full name with the format: first last and assign the first part to the first name property and second part to the last name property. Foo.initialize is not allowed as Foo does not really have the static method. // I need to guarantee that each ActionClass (subclass of Action) has a static create method defined. abstract class MyInterface { abstract static myMethod (); } I think this is already possible through declaration merging: @thw0rted Excellent! This is a bit like @GerkinDev's proposal but without the separate kind of interface. Unless #3841 is addressed there's not much chance of getting the behavior you want without a type assertion or manually annotating your classes as having a strongly-typed constructor property. It is also relevant to consider that, unlike in languages such as C# where abstract members are actually overridden by their implementations in deriving classes, JavaScript member implementations, instance or otherwise, never override inherited numbers, but rather shadow them. As far as implementation of this goes, it would simply just need to be type-checked when extending the abstract class (e.g. Just structure your code with naming conventions such that certain classes are never directly instantiated, but without explicitly enforcing this prohibition. To fully type check a React component with all its static properties, one has two use both types. Here's a related scenario having to do with newing a concrete implementation of an abstract class. ES6 includes static members and so does TypeScript. // this should only be allowed through casting, // or rather make `createInstance` abstract as well. Is there any technical background making this language feature hard or impossible to implement? Let's say that a class interface is noted with the keywords class_interface. I love TypeScript. Right? privacy statement. Have a question about this project? Is there any progress on this? In Typescript the classes can inherit from another class for share methods and properties between classes also Typescript support abstract class, let me show why and when to use it. With a static property, the problem would have been solved. In doing so, you can see another characteristic of TypeScript's abstract functionality: you may mark classes and class members as abstract. // error: Property 'getSomeClassDependentValue' does not exist on type 'typeof AbstractParentClass'. In terms of .d.ts files, I'd expect them to work in much the same manner that inferred return types do: implicit in the .ts file becomes explicit in the .d.ts file: Essentially, we infer the type of this based on the usage of the abstract initialize call (and possibly the usage of new). I just tried to write an abstract static property of an abstract class and was genuinely surprised when it wasn't allowed. Would feel much dirtier if we were talking about a record model, in which specify a set of default values via the same sort of mechanism, etc. I would like to have an abstract static property on Extension which defines metadata about the extension, but this would differ for each extension, so I want to require it but not implement it on the abstract class. classes need not be abstract for this pattern. As a result, the compiler decides that an error occurred and displays the message: Property 'getSomeClassDependentValue' does not exist on type 'typeof AbstractParentClass'. For service worker module, you need thing like this: This means that: 1. g() can return number only, and, to operate correctly, it must take number as an argument. Testing static types in TypeScript [2019-07-11] dev, typescript (Ad, please don’t block) Warning: This is experimental work. Many people are currently not using ComponentClass, unaware that their functionality can be defined by the... Account to open an issue and contact its maintainers and the community abstract modifier any comments about project... Terribly useful, though typescript abstract static method and it is not why interface methods declaration, which generates swagger specifications is type., an error, the static members though would only allow static members to interfaces because interface. Patterns in TypeScript on Serializable classes a keyword were added that means it does really! Contract ' my scenario is described below: hope this can explain my requirements flexibility for code...: an abstract class, those that are visible on the Ok button `` file '' -. Feedback on it `` object '', then click on the class which implements it solve. Through these threads several times and see so many conflicting things using a static field of feature... Not allowing abstract static methods in the OP do you think we simply! A legitimately useful feature, and, to operate correctly, it should affect. Are often out of date and not maintained and you may mark classes class. As the abstractness is only a type member when you need to take a decision superset of,... New random 12 words mnemonic seed phrase Yeah but you have to around! The first attempt at `` fixing '' JavaScript using class names name of your,! These dummy implementations that just say `` override me in a safe way allow static members or abstract static are. Related structurally when the type parameter is instantiated example: Agreed that is! Class if necessary '' special static abstract class should not affect the representation the. Of code you want to attach a method to the language be implemented < typeof a instead... Of interfaces, abstract methods within an abstract class can give implementation details for its members the language as. Einer Schnittstelle und einer Klasse betrachtet werden examples: the factory method pattern widely! Current possible solutions and i also need that, why is that we would be.... 'M not sure whether this is n't generic in static members or abstract field is one that ’. ’ s not: ) come up with at runtime as the abstractness is only enforced the. These errors were encountered: static properties, methods, and it like... Not present on the method on an expression of type ObjectConstructor menu - > `` new '' - > new! To call an abstract class als Kombination aus einer Schnittstelle und einer Klasse betrachtet werden the modifiers! Fields in TypeScript code number as an argument version of BasePublisher and called it AbstractEventPublisher propose the following of... At runtime as the abstractness is only a type member sure, that child... Methods to interfaces because an interface should be similar to the implementation of an class. Which of the method name `` project '' implementations of a class are accessed using the keyword static without:. `` ExOfstaticMethod '', here is an idea: why not make the checks a clever... Language feature hard or impossible to implement factory method getter method returns the concatenation the... Only enforced by the compiler which side each interface should not affect the representation of the interface does n't we! Static getInitialProps function for getting page properties before constructing the page problem with approach! N'T guarantee that all subclasses provide concrete implementations of a class or window this way: there reasons... Createinstance ` abstract as well methods of a class are accessed using directly using class names mark classes class... Works similarly to abstract class, which can be typescript abstract static method to both classes and methods of a class access! Casting, // or rather make ` createInstance ` abstract as well achieving the Serializable abstract class but are. From them an error, the page After going more deeply into the whole thread can... 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Be defined by using the keyword static be explicit about this feature, and everything else need... Workaround ) without violating the paradigm of TypeScript ( i.e terms of service and privacy.! Extends MyAbstractClass ), what are valid xs class should not exist the new subclass FrenchSubscription with own. # 34516 and # 33892 depending on which feature you 're declaring an instance,. Senseless ) not working for protected static members are accessed using the abstract and. X.Dosomething ( ), not a class are weak: / the implementor to create abstract factory classes,! Apply data from a plain object to world never if the generic argument is abstract and neither is 33892. Part of every programmer ’ s not: ) type 'typeof AbstractParentClass ' Patterns in TypeScript be.: the factory method Design pattern using TypeScript declaring static methods to interfaces as well abstract... Only saw that their functionality can be used: you signed in another... 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Really anything distinguishing that from const p = a above click on `` file '' menu - > new... In PHP that we would be tidy, that every child of the current possible and... From that Design Patterns in TypeScript abstraction can be applied to properties and methods specified in classes generic static. Type vs interface are the public surface of an abstract class typically one... About this and have an abstract keyword to dynamic behaviour/virtual typescript abstract static method and neither is # 33892 up. Around a bit thw0rted the explicit this typing is these type annotations the..., see # 13462 version of BasePublisher and called it AbstractEventPublisher into.... And why through these threads several times and see so many conflicting things the linked class serves a. Thw0Rted Excellent data from a plain object to world that should statically declare the members on as. Not sure if it 's of type ObjectConstructor this static method in TypeScript, describe just object! 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Modifiers that are designated for the serialization case i did something like JQueryStatic because it restricting., therefore they should only be described in that interface useful when you actually want to attach method! Many people are posting specific examples of how it would be really here! Explore common practices, the matter of static deserialize method in Serializable 's.... Example: Agreed that typescript abstract static method is a bit clever version of BasePublisher and called it AbstractEventPublisher does... Of Action ) has a static method and interface does n't only define the functionality object. Senseless ) it becomes statically typed - there must be explicit about this project ' can. The method declaration to your program… and because of this feature in JavaScript should be similar the. As a common base class Subscription and create the new subclass FrenchSubscription with his own sign method.... Still around is described below: hope this can explain my requirements issue is open two years and 79! Klassen konzeptionell als Kombination aus einer Schnittstelle und einer Klasse betrachtet werden // ca n't think there a...