Refer to Function type retaining generics

user_14874778 0
Viewed 24

In Typescript, is there a way to refer to a function type with generics, without having to instantiate the generics? (Passing them to be instantiated when the function is actually called).

For example, I have the following type:

type FetchPageData<T> = (client : APIClient<T>) => T;

where APIClient is an abstract class like this:

export abstract class APIClient<T> {

  abstract getData(demoDataIsSelected : boolean, queryParameters ?: ApiQueryParameters) : T;
}

I want to create a function of this type, but if I try:

fetchPageData : FetchPageData = client => {
   return client.getData(x, y);
}

Typescript requires that I provide the generic type for T. What I want is similar to what we do when refering to a function definition, instead of calling it. Similarly I would expect this to refer to the type definition without requiring the T, because the T concerns only the calling of the function.

If not like this, what is the syntax for me to get a T and pass it to FetchPageData on the instantiation? (It has to be with const syntax, instead of function, because I'm actually asigning with useCallback on react)

typescript
1 Answers

I figured it out right after posting this:

By putting the <T> before the equal sign, I was using T as a generic for the creation of the function, instead of defining the FetchPageData as a function type that takes a generic argument. The correct syntax would be:

type FetchPageData = <T>(client : APIClient<T>) => T;
user_148747780
Related