How to add the error type of useQueries in TypeScript?

In TypeScript, handling error types for useQueries requires understanding that useQueries is a feature from the React Query library, enabling parallel execution of multiple asynchronous queries. To implement type-safe error handling for these queries, ensure React Query and TypeScript are installed in your project.

Step 1: Install necessary libraries

If not already installed, use the following command:

bash
npm install react-query
# or
yarn add react-query

Ensure your project is configured with TypeScript.

Step 2: Use useQueries and add error types

When using useQueries in TypeScript, define input and output types for query functions, and specify error types. Here is an example using useQueries with error type definitions:

typescript
import { useQueries, UseQueryResult } from 'react-query';
import axios from 'axios';

interface Data {
    id: number;
    name: string;
}

interface Error {
    message: string;
}

const fetchUserData = async (userId: number): Promise<Data> => {
    const response = await axios.get<Data>(`https://api.example.com/users/${userId}`);
    return response.data;
};

export function useUserData(userIds: number[]) {
    return useQueries(
        userIds.map(id => ({
            queryKey: ['user', id],
            queryFn: () => fetchUserData(id),
            select: (data: Data) => ({ id: data.id, name: data.name }),
            onError: (err: Error) => {
                console.error(`Failed to fetch data for user ${id}: ${err.message}`);
            }
        }))
    ) as UseQueryResult<Data, Error>[];
}

Explanation

• Data and Error types: These define the structure for successful API responses (Data) and error objects (Error).
• fetchUserData function: An asynchronous function using axios to fetch data, returning a Data-typed object.
• useQueries: This hook executes multiple queries in parallel. Each query is configured with:
  • queryKey: A unique identifier for the query.
  • queryFn: The function to fetch data.
  • select: An optional transformation function for data.
  • onError: An error handler receiving an Error-typed parameter.

This setup ensures type-safe API calls, handles potential errors effectively, and provides specific error messages. Type protection and error handling help developers identify issues early, resulting in more robust and maintainable code.