How to Fix localStorage is not defined Error in Angular Applications

Learn how to resolve the `localStorage` error in your Angular application when using Server-Side Rendering (SSR) with our comprehensive guide.
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How to Fix the localStorage is not defined Error in Angular Applications

When developing Angular applications, it's common to utilize localStorage for storing data in the browser. However, many developers encounter an error that states "ERROR ReferenceError: localStorage is not defined". This issue typically arises when using Server-Side Rendering (SSR), as localStorage is part of the browser's window object and isn't available on the server.

In this guide, we will explore why this error occurs and provide clear solutions to help you solve the problem effectively.

Understanding the Problem

The error occurs because Angular applications can be rendered both in the browser and on the server. When trying to access localStorage in a server context (where there’s no concept of a browser), it leads to a ReferenceError. Thus, to handle this scenario effectively, you need to determine when your code is running in a browser environment.

Common Causes of the Error

Using localStorage directly in a global context: Accessing localStorage without checking if the code is executing in a browser.

Server-Side Rendering (SSR): During SSR, your Angular code is being executed on the server where localStorage does not exist.

Solution Overview

To solve the localStorage error, you can implement the following strategies:

Check for Browser Environment: Before interacting with localStorage, check if the code is running in a browser.

Use Dependency Injection: Leverage Angular’s dependency injection capabilities to determine the platform.

Solution 1: Checking for Browser Environment

Modify your LocalStorageService to check if it's running in a browser before accessing localStorage. Here’s how to do it:

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

Explanation of the Code:

PLATFORM_ID: This is injected to determine the runtime environment.

isPlatformBrowser: A utility function that checks if your code is running in a browser. If it is, you can safely access localStorage.

Solution 2: Mocked localStorage

If you require localStorage functionality on the server (e.g., for tests), consider mocking it. You can provide a factory for localStorage:

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

Conclusion

By implementing these strategies, you should be able to resolve the localStorage is not defined error in your Angular applications when using SSR. Always ensure that you check the runtime environment to maintain a seamless experience across various platforms.

Now that you have the solutions laid out, you can confidently utilize localStorage in your Angular application without running into errors!