Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
import { useState } from 'react';
// Usage
function App() {
// Similar to useState but first arg is key to the value in local storage.
const [name, setName] = useLocalStorage('name', 'Bob');
return (
<div>
<input
type="text"
placeholder="Enter your name"
value={name}
onChange={e => setName(e.target.value)}
/>
</div>
);
}
// Hook
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);
}
};
return [storedValue, setValue];
}
@Richard87
Copy link

Hi all!

I would like to sugest a minor improvement to the setValuemethod:
instead of this:

    const setValue = (value: any) => {
        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
        if (typeof window !== 'undefined') {
          window.localStorage.setItem(key, JSON.stringify(valueToStore))
        }
        } catch (error) {
            // A more advanced implementation would handle the error case
            console.log(error)
        }
    }

I suggest this:

    const setValue = (value: any) => {
        try {
            setStoredValue(latestValue => {
                const valueToStore = value instanceof Function ? value(latestValue) : value

                // Save to local storage
                if (typeof window !== 'undefined') {
                    window.localStorage.setItem(key, JSON.stringify(valueToStore))
                }

                return valueToStore
            })
        } catch (error) {
            // A more advanced implementation would handle the error case
            console.log(error)
        }
    }

The purpose is to have access to the real previous value in the callback method :)

Copy link

ghost commented Jun 17, 2022

I think this implementation has a small flaw in that you are assuming storedValue is up to date when you call

const valueToStore = value instanceof Function ? value(storedValue) : value

Probably better to use useEffect with a dependency on the value of useState and write the value there to localstorage instead.

@Klaasvaak
Copy link

When using this hook in an application and over time changing the object that is managed it will still return the object from localstorage which will miss the newly added property.
For example on my first day I commit using this hook:

useLocalStorage("example", { test: "hello" })

I deploy this code.
The next day I change the usage of this hook:

useLocalStorage("example", { test: "hello", somethingNew: "this was just added" })

Because I have test: "hello" in my storage, this won't return the initial value for somethingNew.

2 possible solutions:

  1. the consumer of this hook should change the storage key every time this is done
  2. change return item ? JSON.parse(item) : initialValue; to return item ? { ...initialValue, ...JSON.parse(item)} : initialValue;

There is also the problem when removing an attribute it will still return it, but this might be less problematic.

@AngelAlexQC
Copy link

You can sync the state of localStorage between all tabs that application is opened.
My solution was:

import { useEffect, useState } from "react";

const useLocalStorage = (key, initialValue) => {
    // State to store our value
    // Pass initial state function to useState so logic is only executed once
    const [storedValue, setStoredValue] = useState(() => {
        if (typeof window === "undefined") {
            return initialValue;
        }
        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
            if (typeof window !== "undefined") {
                window.localStorage.setItem(key, JSON.stringify(valueToStore));
            }
        } catch (error) {
            // A more advanced implementation would handle the error case
            console.log(error);
        }
    };

    // Sync localStorage between tabs
    useEffect(() => {
        const listener = (e) => {
            if (e.key === key) {
                setStoredValue(JSON.parse(e.newValue));
            }
        };
        window.addEventListener("storage", listener);
        return () => {
            window.removeEventListener("storage", listener);
        };
    }
        , [
            key,
            initialValue,
        ]);

    return [storedValue, setValue];
};

export default useLocalStorage;

@ris58h
Copy link

ris58h commented Sep 13, 2022

Could we add a custom serialization/deserialization logic?
function useLocalStorage(key, initialValue, serialize = JSON.stringify, deserialize = JSON.parse) {
And use those functions instead of calling JSON.stringify/JSON.parse.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment