How to type response from useInfiniteQuery QueryFn?

In using useInfiniteQuery from the react-query library to fetch data, properly modeling the response type for QueryFn is crucial. This ensures that your application can handle data in a type-safe manner and integrate seamlessly with TypeScript.

Basic Steps:

1. Define the response data type:
   In TypeScript, first define an interface or type that details the expected response structure of the QueryFn function.

2. Apply this type to useInfiniteQuery:
   Use generic parameters to apply this type to useInfiniteQuery, ensuring the response data adheres to the defined type.

Example:

Suppose we are retrieving a series of article data from an API, where each article object contains id, title, and author properties. We can define the TypeScript interface as follows:

typescript
interface Article {
  id: number;
  title: string;
  author: string;
}

interface ArticlesResponse {
  page: number;
  articles: Article[];
}

Then, we can define an asynchronous function to fetch these articles, which accepts the current page number as a parameter:

typescript
async function fetchArticles(pageParam: number): Promise<ArticlesResponse> {
  const response = await fetch(`https://api.example.com/articles?page=${pageParam}`);
  if (!response.ok) {
    throw new Error('Network response was not ok');
  }
  return response.json();
}

Finally, we use useInfiniteQuery and specify the ArticlesResponse type:

typescript
import { useInfiniteQuery } from 'react-query';

function useInfiniteArticles() {
  return useInfiniteQuery<ArticlesResponse, Error>({ 
    queryKey: ['articles'],
    queryFn: ({ pageParam = 1 }) => fetchArticles(pageParam),
    getNextPageParam: (lastPage, allPages) => lastPage.page + 1
  });
}

In this example, we clearly define the types for each part, from the API response data structure (ArticlesResponse) to the asynchronous function (fetchArticles) and the final useInfiniteQuery call. This ensures that your code is not only more maintainable but also leverages TypeScript's type checking and auto-completion features, reducing runtime errors.