<pre class="language-typescript"><code class="language-typescript">import { useEffect, useState } from "react";

export function useSWR&lt;T = any, E = any&gt;(
 _key: string,
 fetcher: () =&gt; T | Promise&lt;T&gt;
): {
 data?: T
 error?: E
} {
 const [data,setData] = useState&lt;T | undefined&gt;();
 const [error,setError] = useState&lt;E | undefined&gt;();

 const result = fetcher();
 const resultIsPromise = result instanceof Promise;

 

 useEffect(()=&gt;{
 if(resultIsPromise){
 result.then(setData,setError)
 }
 },[])

 return {data: resultIsPromise ? data: result, error}

}

// if you want to try your code on the right panel
// remember to export App() component like below



</code></pre>

isPromise

SWR is a popular library of data fetching. Let's try to implement the basic usage by ourselves. import React from 'react' function App() { const { dat…