What is React Query or SWR

Both React Query and SWR are libraries designed to handle data fetching and state management for server-side data in React applications. They aim to simplify and enhance the process of fetching, caching, and updating remote data, often replacing traditional approaches like useEffect and local state management.

React Query is a data-fetching library with powerful tools for managing server-side state. It provides declarative APIs for fetching, caching, synchronizing, and updating data in React applications.

Key Features of React Query

Data Caching

Automatically caches responses and serves cached data while re-fetching in the background.

Stale-While-Revalidate

Ensures the UI always shows the freshest possible data.

Automatic Refetching

Automatically refetches data when components mount or network conditions change.

Mutations

Simplifies handling updates to server-side data with tools for POST/PUT/DELETE operations.

Pagination & Infinite Loading

Handles paginated data and infinite scrolling seamlessly.

DevTools Integration

Includes a helpful debugging tool to visualize query states.

import { useQuery } from 'react-query';
import axios from 'axios';

const fetchUsers = async () => {
  const { data } = await axios.get('/api/users');
  return data;
};

const Users = () => {
  const { data, error, isLoading } = useQuery('users', fetchUsers);

  if (isLoading) return <p>Loading...</p>;
  if (error) return <p>Error: {error.message}</p>;

  return (
    <ul>
      {data.map((user) => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
};

What is SWR

SWR (Stale-While-Revalidate) is another library for fetching and managing remote data. It is developed by the team at Vercel and inspired by HTTP caching mechanisms. Like React Query, SWR aims to simplify server-side state management but with a lightweight API and focus on simplicity.

Key Features of SWR

Stale-While-Revalidate

Optimizes data fetching by serving cached data while revalidating in the background.

Focus/Online Revalidation

Automatically refetches data when the window regains focus or the user comes back online.

Automatic Caching

Caches and reuses fetched data across components.

Data Mutation

Supports updating local data instantly and syncing it with the server later.

Minimal API

Extremely simple to use with fewer concepts to learn.

import useSWR from 'swr';
import axios from 'axios';

const fetcher = (url) => axios.get(url).then((res) => res.data);

const Users = () => {
  const { data, error, isLoading } = useSWR('/api/users', fetcher);

  if (isLoading) return <p>Loading...</p>;
  if (error) return <p>Error: {error.message}</p>;

  return (
    <ul>
      {data.map((user) => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
};

Similarities Between React Query and SWR

Both libraries are excellent choices for handling server-side state and share the following features:

• Data Caching: Both cache fetched data to minimize network requests.
• Stale-While-Revalidate: Show cached data instantly while refetching fresh data in the background.
• Focus/Online Revalidation: Automatically refetch data when the app regains focus or the user reconnects to the internet.
• Error Handling: Provide built-in mechanisms to handle fetch errors.
• Developer Experience: Offer excellent developer tools (React Query has its own DevTools, while SWR integrates seamlessly with browser dev tools).

Differences Between React Query and SWR

Feature	React Query	SWR
Complexity	Offers more advanced features (mutations, pagination).	Simpler and more lightweight.
Focus	Comprehensive server-side state management.	Lightweight data fetching with caching.
Mutations	Built-in tools for POST/PUT/DELETE.	Requires manual updates to cache after mutation.
Pagination/Infinite Scroll	Built-in support for paginated/infinite loading.	Requires custom implementation for pagination.
DevTools	Provides React Query DevTools for debugging.	No dedicated DevTools, integrates with browser dev tools.
API Flexibility	Can be customized heavily to match complex needs.	Minimal and opinionated API.