useEffect does not listen for localStorage

Question

I'm making an authentication system and after backend redirects me to the frontend page I'm making API request for userData and I'm saving that data to localStorage. Then I'm trying to load Spinner or UserInfo.

I'm trying to listen for the localStorage value with useEffect, but after login I'm getting 'undefined'. When the localStorage value is updated useEffect does not run again and Spinner keeps spinning forever.

I have tried to do: JSON.parse(localStorage.getItem('userData')), but then I got a useEffect infinite loop.

Only when I'm refreshing the page does my localStorage value appear and I can display it instead of Spinner.

What I'm doing wrong?

Maybe there is a better way to load userData when it's ready?

I'm trying to update DOM in correct way?

Thanks for answers ;)

import React, { useState, useEffect } from 'react';
import { Spinner } from '../../atoms';
import { Navbar } from '../../organisms/';
import { getUserData } from '../../../helpers/functions';

const Main = () => {
  const [userData, setUserData] = useState();
  useEffect(() => {
    setUserData(localStorage.getItem('userData'));
  }, [localStorage.getItem('userData')]);

  return <>{userData ? <Navbar /> : <Spinner />}</>;
};

export default Main;

Answer 1

It would be better to add an event listener for localstorage here.

useEffect(() => {
  function checkUserData() {
    const item = localStorage.getItem('userData')

    if (item) {
      setUserData(item)
    }
  }

  window.addEventListener('storage', checkUserData)

  return () => {
    window.removeEventListener('storage', checkUserData)
  }
}, [])

Answer 2

Event listener to 'storage' event won't work in the same page

The storage event of the Window interface fires when a storage area (localStorage) has been modified in the context of another document.

https://developer.mozilla.org/en-US/docs/Web/API/Window/storage_event

Answer 3

The solution is to use this structure:

useEffect(() => {
    window.addEventListener("storage", () => {
      // When storage changes refetch
      refetch();
    });

    return () => {
      // When the component unmounts remove the event listener
      window.removeEventListener("storage");
    };
}, []);