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Discover effective strategies to manage expired JWT tokens in Axios with interceptors and avoid unhandled promise rejections.
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Handling Axios Errors: How to Manage Token Expiration with Interceptors

Working with API requests in a JavaScript application often involves handling authentication tokens neatly, especially when dealing with JWT (JSON Web Tokens). A common issue developers face is handling token expiration when using Axios, a popular HTTP client for JavaScript. In this guide, we'll explore a specific scenario where you're implementing jwt token refresh logic and how you can improve it to avoid unhandled promise rejections when the expired token is encountered.

The Problem: Error is Caught but Not Handled

You have set up an error interceptor in Axios to refresh your authentication token when it expires. The refreshing logic seems to work flawlessly as it intercepts the error, retrieves a new token, and then retries the original request successfully. However, the challenge lies in the fact that the calling function still receives the error, even if the request is retried successfully. This leads to confusion as you would expect handling for the error to ensure there are no unhandled rejections.

The Structure of the Solution

Here’s how to properly manage the refreshed token and avoid the original request throwing an error after the interceptor has already handled it. We’ll look at the primary parts of the interceptor that need some adjustments to return the correct results without further rejection.

Modifying the Axios Response Interceptor

In your Axios configuration, there are two main segments in the response interceptor: one that handles successful responses and another that deals with errors. The latter part must be modified to ensure that you return the result of the retried request as intended.

Here's the modified code snippet you need:

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Key Adjustments Made

Return the result of the retried request: Instead of missing the return statement where you make the original request again, ensure you include a return for the axios.request(originalRequest);. This effectively passes the response back to the calling function.

Improved Error Handling: Enhanced readability and organization ensure you explicitly handle different error scenarios, making the code easier to follow and maintain.

Token Management: By updating the tokens in local storage upon successful refresh, you ensure your application always has the latest credentials for subsequent requests.

A Practical Example: Sending Requests

Here is an example function showing how you can call a post request while utilizing the config we discussed:

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Conclusion

Managing token expiration with Axios interceptors can seem tricky, but implementing proper error handling ensures that the user experience remains seamless. With the adjustments made to the response interceptor, you can catch and refresh your JWT tokens without unresolved rejections, ultimately leading to a more robust and user-friendly application.

Final Thoughts

As you continue to develop your applications with Axios, always remember the importance of handling promises correctly, especially when working with authentication and tokens. This ensures that users don't encounter unexpected errors, providing them with a smoother experience overall. Happy coding!