Creating a Custom React Hook for Persistent Local Storage

Let's create a custom React hook called useLocalStorage. This hook will allow you to store and retrieve data from the local storage of the browser. It's a very useful hook as it abstracts the complexity of using local storage and provides a simple API similar to useState.

import { useState, useEffect } from 'react';

function useLocalStorage(key, initialValue) {
  // State to store our value
  // Pass initial state function to useState so logic is only executed once
  const [storedValue, setStoredValue] = useState(() => {
    try {
      // Get from local storage by key
      const item = window.localStorage.getItem(key);
      // Parse stored json or if none return initialValue
      return item ? JSON.parse(item) : initialValue;
    } catch (error) {
      // If error also return initialValue
      console.log(error);
      return initialValue;
    }
  });

  // Return a wrapped version of useState's setter function that ...
  // ... persists the new value to localStorage.
  const setValue = (value) => {
    try {
      // Allow value to be a function so we have same API as useState
      const valueToStore =
        value instanceof Function ? value(storedValue) : value;
      // Save state
      setStoredValue(valueToStore);
      // Save to local storage
      window.localStorage.setItem(key, JSON.stringify(valueToStore));
    } catch (error) {
      // A more advanced implementation would handle the error case
      console.log(error);
    }
  };

  useEffect(() => {
    window.localStorage.setItem(key, JSON.stringify(storedValue));
  }, [key, storedValue]);

  return [storedValue, setValue];
}

You can use this hook in the same way you use the useState hook. Here's an example:

function Component() {
  const [name, setName] = useLocalStorage('name', 'Bob');

  return (
    <div>
      <p>Hello, {name}!</p>
      <button onClick={() => setName('Alice')}>Change name</button>
    </div>
  );
}

In this example, the name will be persisted in local storage. Even if you refresh the page, the name will still be there.