SWR

import { useState, useEffect } from 'react';

#include <iostream>

#include <stdio.h>

#include <stdio.h>

The name “SWR” is derived from stale-while-revalidate, a HTTP cache invalidation strategy popularized by HTTP RFC 5861. SWR is a strategy to first return the data from cache (stale), then send the fetch request (revalidate), and finally come with the up-to-date data.

Overview

import useSWR from 'swr'
 
function Profile() {
  const { data, error } = useSWR('/api/user', fetcher)
 
  if (error) return <div>failed to load</div>
  if (!data) return <div>loading...</div>
  return <div>hello {data.name}!</div>
}

import useSWR from 'swr'
 
function Profile() {
  const { data, error } = useSWR('/api/user', fetcher)
 
-  if (error) return <div>failed to load</div>
+  if (!data) return <div>loading...</div>
  return <div>hello {data.name}!</div>
}

In this example, the useSWR hook accepts a key string and a fetcher function. key is a unique identifier of the data (normally the API URL) and will be passed to fetcher. fetcher can be any asynchronous function which returns the data, you can use the native fetch or tools like Axios.

The hook returns 2 values: data and error, based on the status of the request.

Features

With just one single line of code, you can simplify the logic of data fetching in your project, and also have all these amazing features out-of-the-box:

• Fast, lightweight and reusable data fetching
• Built-in cache and request deduplication
• Real-time experience
• Transport and protocol agnostic
• SSR / ISR / SSG support
• TypeScript ready
• React Native

SWR has you covered in all aspects of speed, correctness, and stability to help you build better experiences:

• Fast page navigation
• Polling on interval
• Data dependency
• Revalidation on focus
• Revalidation on network recovery
• Local mutation (Optimistic UI)
• Smart error retry
• Pagination and scroll position recovery
• React Suspense

And a lot more.

Community

SWR is created by the same team behind Next.js, the React framework. Follow @vercel on Twitter for future project updates.

Feel free to join the discussions on GitHub!