As a Next.js app can be executed on both the server and the client side. When the app is rendered on the server, there is no access to the browser-specific features like localStorage, as it is a feature of the client-side browser environment.

So let's say, if we try to use localStorage in a Next.js app, we may encounter issues when the app is being server-side rendered.

To avoid this problem, we can check if localStorage is available before using it in our Next.js app.

if(typeoflocalStorage!== 'undefined') { 
// Use localStorage here
} 

This way, our app will only use localStorage when it is available, and avoid errors when it is not.