Why is localStorage getting cleared whenever I refresh the page?

Question

Like the title says, the localStorage I set registers the changes made to the todoList array and JSON.stringifys it; however, whenever I refresh the page the array returns to the default [] state.

const LOCAL_STORAGE_KEY = "task-list"

function TodoList() {
    const [todoList, setTodoList] = useState([]);

    useEffect(() => {
        const storedList = JSON.parse(localStorage.getItem(LOCAL_STORAGE_KEY));
        if (storedList) {
            setTodoList(storedList);
        }
    }, []);
    
    useEffect(() => {
        localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(todoList));
    }, [todoList]);

Answer 1

When you reload the app/component both effects will run, and React state updates are processed asynchronously, so it's picking up the empty array state persisted to localStorage before the state update is processed. Just read from localStorage directly when setting the initial todoList state value.

Example:

const LOCAL_STORAGE_KEY = "task-list"

function TodoList() {
  const [todoList, setTodoList] = useState(() => {
    return JSON.parse(localStorage.getItem(LOCAL_STORAGE_KEY)) || []
  });
    
  useEffect(() => {
    localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(todoList));
  }, [todoList]);

  ...