DEV Community

Cover image for How to use Local Storage in Next.js
collegewap
collegewap

Posted on • Updated on • Originally published at codingdeft.com

How to use Local Storage in Next.js

Have you received the following error while using local storage in Next.js?



ReferenceError: localStorage is not defined


Enter fullscreen mode Exit fullscreen mode

In this article, we will see how to use local storage in Next.js

Project set up

Create a Next.js application using the following command:



npx create-next-app next-local-storage


Enter fullscreen mode Exit fullscreen mode

Update index.js with the following code:



import { useState } from "react"

export default function Home() {
  let value
  // Get the value from local storage if it exists
  value = localStorage.getItem("favoriteNumber") || ""

  // Set the value received from the local storage to a local state
  const [favoriteNumber, setFavoriteNumber] = useState(value)

  // When user submits the form, save the favorite number to the local storage
  const saveToLocalStorage = e => {
    e.preventDefault()
    localStorage.setItem("favoriteNumber", favoriteNumber)
  }

  return (
    <div>
      <label htmlFor="number">Your favorite number</label>
      <form onSubmit={saveToLocalStorage}>
        <input
          id="number"
          value={favoriteNumber}
          onChange={e => setFavoriteNumber(e.target.value)}
        />
        <input type="submit" value="Save" />
      </form>
    </div>
  )
}


Enter fullscreen mode Exit fullscreen mode

Now if you run the code, you will get the following error:

ReferenceError: localStorage is not defined

Why does the error occur?

The error occurs because the code gets compiled in the server (in localhost or server-side rendering in production), localStorage object does not exist.

The fix

There are multiple ways in which it can be fixed.

Checking if the window is defined

localStorage is an object inside the window object. The window object will not be defined in the server and hence the localStorage code will not be executed in the server.



if (typeof window !== "undefined") {
  value = localStorage.getItem("favoriteNumber") || ""
}


Enter fullscreen mode Exit fullscreen mode

Using try-catch block

We can use a try-catch block to surround the localStorage access:



try {
  value = localStorage.getItem("favoriteNumber") || ""
} catch (error) {}


Enter fullscreen mode Exit fullscreen mode

Using a useEffect hook

You can use a useEffect hook to get the localStorage content. The useEffect hook will not be run in the server and hence no possibility of the error.



import { useEffect, useState } from "react"

export default function Home() {
  // Set the value received from the local storage to a local state
  const [favoriteNumber, setFavoriteNumber] = useState("")

  useEffect(() => {
    let value
    // Get the value from local storage if it exists
    value = localStorage.getItem("favoriteNumber") || ""
    setFavoriteNumber(value)
  }, [])

  // When user submits the form, save the favorite number to the local storage
  const saveToLocalStorage = e => {
    e.preventDefault()
    localStorage.setItem("favoriteNumber", favoriteNumber)
  }

  return (
    <div>
      <label htmlFor="number">Your favorite number</label>
      <form onSubmit={saveToLocalStorage}>
        <input
          id="number"
          value={favoriteNumber}
          onChange={e => setFavoriteNumber(e.target.value)}
        />
        <input type="submit" value="Save" />
      </form>
    </div>
  )
}


Enter fullscreen mode Exit fullscreen mode

Using a custom hook

You can use a custom hook to access local storage as well



import { useState } from "react"

const useLocalStorage = (key, initialValue) => {
  const [state, setState] = useState(() => {
    // Initialize the state
    try {
      const value = window.localStorage.getItem(key)
      // Check if the local storage already has any values,
      // otherwise initialize it with the passed initialValue
      return value ? JSON.parse(value) : initialValue
    } catch (error) {
      console.log(error)
    }
  })

  const setValue = value => {
    try {
      // If the passed value is a callback function,
      //  then call it with the existing state.
      const valueToStore = value instanceof Function ? value(state) : value
      window.localStorage.setItem(key, JSON.stringify(valueToStore))
      setState(value)
    } catch (error) {
      console.log(error)
    }
  }

  return [state, setValue]
}

export default useLocalStorage


Enter fullscreen mode Exit fullscreen mode

In index.js, you can use it as follows:



import useLocalStorage from "@/hooks/useLocalStorage"
import { useState } from "react"

export default function Home() {
// Get the value from local storage if it exists
const [value, setValue] = useLocalStorage("favoriteNumber", "")

// Set the value received from the local storage to a local state
const [favoriteNumber, setFavoriteNumber] = useState(value)

// When user submits the form, save the favorite number to the local storage
const saveToLocalStorage = e => {
e.preventDefault()
setValue(favoriteNumber)
}

return (
<div>
<label htmlFor="number">Your favorite number</label>
<form onSubmit={saveToLocalStorage}>
<input
id="number"
value={favoriteNumber}
onChange={e => setFavoriteNumber(e.target.value)}
/>
<input type="submit" value="Save" />
</form>
</div>
)
}

Enter fullscreen mode Exit fullscreen mode




Source code and Demo

You can view the complete source code here and a demo here

Top comments (14)

Collapse
 
prems5 profile image
PREM KUMAR • Edited

from next js 13 you must use

'use client'
Enter fullscreen mode Exit fullscreen mode

on top of the file

and it will work without any error and it's more cleaner solution

Collapse
 
professor12 profile image
Badejo Emmanuel Adewale

It will have an error in development mode since the component would still run on the server

Collapse
 
pablojsx profile image
Pablojsx

does 'use client' works with nextjs pages? I'm a bit confused

Collapse
 
prems5 profile image
PREM KUMAR

Yes, it works on the new routes folder. Where all the components are server components by default. You need to specify use client
To make it as a client side component

Thread Thread
 
pablojsx profile image
Pablojsx

sorry I mean pages router not nextjs pages, is it an app router thing only?

Collapse
 
mmvlad profile image
Vladyslav Melnychenko

This must be a joke.

How bad the framework needs to be if you can't use localstorage in 1 line of code.

Collapse
 
lmish profile image
lmish

How good framework needs to be if you can use local storage with a server side rendering.

Collapse
 
pickyourdestiny profile image
pickyourdestiny • Edited

I think conceptually its important to understand that you need to save the form data to local storage when the form field data changes during a client event (like submitting the form or making changes to form fields). With pure react you were able to update local storage using useEffect when the form object changes but this wont work in NextJS because the form object will clear (and hence nullify form fields in local storage) on initial component load before hydrating the client.

Takeaway approach (which is provided in this article): One useEffect to retrieve the local storage value if local storage is populated, and only write to local storage during a client event.

Collapse
 
vulcanwm profile image
Medea

really helpful post!

Collapse
 
muhammadasif_wd profile image
Muhammad Asif

Thanks for this. working code.

Collapse
 
alisina123 profile image
Alisina Sadat

how to use Middle ware localstorage ?

Collapse
 
reddash99 profile image
RedDash99

Thank you for the useful hook, it works perfectly!

Collapse
 
prat1kgupta profile image
pratik gupta

custom hook method is not working🥲

Collapse
 
collegewap profile image