how does swr or useSWR works properly in reactjs / nextjs?

Question

In the fisrt part I ma suign fetch() and it is working fine but whe i use useSWR() it returns UNDEFINED

export const getAllEvents = async()=>{
    const response = await fetch('https://*******-rtdb.firebaseio.com/events.json');
    const data = await response.json();
    const events = [];

    for (const key in data){
        events.push({
            id:key,
            ...data[key]
        });
    }
    return events; // returns data as I wanted.. perfect
}

but in the following snippet it returns undefined (the same url)

import useSWR from 'swr';
const {data, error} = useSWR('https://*******-rtdb.firebaseio.com/events.json');
console.log(data);  // returns undefined

Answer 1

useSWR expects fetcher function as second argument:

https://swr.vercel.app/#overview

It can be a custom method e.g.

export const fetcher = async (...args: Parameters<typeof fetch>) => {
  const res = await fetch(...args);
  if (!res.ok) {
    throw { status: res.status, statusText: res.statusText };
  }
  return res.json();
};

Answer 2

Use swr also needs to take a fetcher function, right now you're just passing down a url. Swr doesnt know what to do with that url..

const { data, error } = useSWR(
    "https://api.github.com/repos/vercel/swr",
    fetcher
  );


const fetcher = (url) => fetch(url).then((res) => res.json());

I suggest you read the docs.

Answer 3

add this :

const fetcher = (...args) => fetch(...args).then(res => res.json())
const {data, error} = useSWR('https://*******-rtdb.firebaseio.com/events.json', fetcher);