Solving the localStorage is not defined Issue in Next.js with useReducer

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Introduction

Understanding the Issue

When you try to access localStorage directly during server-side rendering, you will face a reference error because localStorage is not defined in that environment.

The Solution

To resolve the issue of accessing localStorage within useReducer, we can implement a conditional check to ensure that the code only runs on the client side. Here’s how to do that step-by-step:

Step 1: Modify the useReducer Initialization

Instead of directly attempting to access localStorage, you can check if the window object is defined. This enables you to safely connect to localStorage only when your code is running in the browser. Here’s an updated snippet:

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In this code:

We are checking if window is defined.

If it is, we proceed to retrieve the cart items from localStorage. If not, we initialize the state to an empty array.

Step 2: Creating a Reusable Constant (Optional)

To keep your code DRY (Don't Repeat Yourself), you can create a reusable constant that indicates if the code is running on the client-side:

[[See Video to Reveal this Text or Code Snippet]]

Use this constant throughout your application wherever you need to interact with browser-specific APIs.

Important Notes

Remember that this solution only works when the code is executed on the client side. Make sure to avoid any references to localStorage during server-side rendering.

Utilize the useEffect hook to synchronize localStorage with your component state. Whenever the state changes, you can save the updated cart items back to localStorage:

[[See Video to Reveal this Text or Code Snippet]]

This ensures that the cart items are preserved even after the user reloads the page.

Conclusion