Reactjs getting 401 error only at the first time

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31-08-2024

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Reactjs 401 Error on First Load: A Common MERN Stack Problem and Solution

It's frustrating to encounter a 401 Unauthorized error in your React application, especially when it only happens the first time you access a specific resource. This issue is quite common in MERN stack projects, where you're likely dealing with user authentication and data fetching from a backend server.

Let's delve into the root cause of this problem, inspired by a Stack Overflow question [link to original question], and explore a solution.

Understanding the Scenario

The provided code snippets show a typical MERN stack setup:

• Authentication: The AuthContextProvider uses a useReducer hook to manage authentication state (user, token, role). The state is persisted in localStorage for session management.
• Data Fetching: The useFetchData custom hook fetches data from an API endpoint. It includes authentication by attaching the Authorization header with a bearer token.
• Component: The component displays user profile data retrieved using useFetchData.

The problem lies in the interaction between the authentication state and data fetching on initial page load. Let's break it down:

1. Initial Load: On the first page load, the authentication state might not be fully initialized yet. This could be due to the localStorage retrieval process taking a short time or other factors.
2. First Request: Your component tries to fetch user data using useFetchData. Since the authentication state is still being set, the token might be missing or not completely available, leading to the 401 error.
3. Refresh: When you refresh the page, the authentication state has had time to initialize properly, the token is present, and the data fetch succeeds.

The Solution: Conditional Data Fetching

The issue arises because you're attempting to fetch data before the authentication state is fully established. To resolve this, you can modify the useFetchData hook to conditionally fetch data only when the authentication token is available:

import { useEffect, useState } from "react";
import { token } from "../config";

const useFetchData = (url) => {
  const [data, setData] = useState([]);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(null);

  useEffect(() => {
    const fetchData = async () => {
      if (token) { // Check if token is available
        setLoading(true);
        try {
          const res = await fetch(url, {
            headers: { Authorization: `Bearer ${token}` },
          });

          const result = await res.json();

          if (!res.ok) {
            throw new Error(result.message + " Failed");
          }
          setData(result.data);
          setLoading(false);
        } catch (err) {
          setLoading(false);
          setError(err.message);
        }
      }
    };

    fetchData();
  }, [url, token]); // Include token in dependency array

  return {
    data,
    loading,
    error,
  };
};

export default useFetchData;

Explanation

• Token Check: We've added a condition if (token) inside fetchData. This ensures that data is fetched only when the authentication token is present.
• Dependency Array: The token is now included in the useEffect dependency array, meaning fetchData will be re-executed whenever the token changes.

Additional Recommendations

• Error Handling: Implement robust error handling to display meaningful messages to the user when a 401 error occurs.
• Loading State: Use a loading indicator to provide feedback while data is being fetched.
• Data Caching: Consider caching fetched data to improve performance on subsequent requests, especially if the data is likely to remain the same for a while.

Conclusion

By implementing conditional data fetching based on the availability of the authentication token, you can resolve the 401 error that occurs only on the first page load. This approach ensures that data is fetched only when the authentication state is fully initialized, leading to a more reliable and user-friendly experience.