Axios Interceptors Explained

Axios is a popular JavaScript library used for making HTTP requests from a web browser or Node.js environment. It provides a simple, elegant API for sending and receiving HTTP requests that makes it easy to communicate with APIs, web services, and other remote resources.

One of the key features of Axios is its support for interceptors. Interceptors are essentially middleware functions that can intercept and modify requests and responses before they are sent or received. In this article, we'll explore how Axios interceptors work and how they can be used to implement middleware-style functionality in your web applications.

What are interceptors?

Axios interceptors are functions that can be registered globally or locally for a specific Axios instance. They allow you to intercept HTTP requests and responses before they are handled by your application, providing a way to modify headers, add authorization tokens, handle errors, and more.

Interceptors work by "intercepting" the request or response before it is processed by the application, allowing you to modify it in some way. You can register multiple interceptors for a single Axios instance, and they will be executed in the order they were registered.

In many ways, interceptors in Axios function similarly to middleware in other web development frameworks. Middleware functions intercept incoming requests and outgoing responses and modify them as needed, allowing developers to add common functionality to their applications without having to repeat the same code in multiple places.

Request interceptors

Axios provides a request interceptor that allows you to modify the request before it is sent. This can be useful for adding common headers, modifying the URL or parameters, or handling authentication tokens.

For example, suppose you want to add an authentication token to every request in your application. You could use the following code to add an Authorization header with the token:

axios.interceptors.request.use(config => {
  const token = localStorage.getItem('token');
  if (token) {
    config.headers.Authorization = `Bearer \${token}`;
  }
  return config;
});

In this code, we’re using the axios.interceptors.request.use() method to add a request interceptor that checks for an authentication token in the localStorage and adds it to the request headers if it exists. This will ensure that the token is included with every request sent by the application.

Response interceptors

Axios also provides a response interceptor that allows you to modify the response before it is processed by your application. This can be useful for handling errors, transforming data, or adding additional metadata to the response.

For example, suppose you want to handle errors in a specific way in your application. You could use the following code to add a response interceptor that checks for specific error codes and handles them accordingly:

axios.interceptors.response.use(response => {
  return response;
}, error => {
  if (error.response.status === 401) {
    // Redirect to login page
  } else if (error.response.status === 404) {
    // Handle not found error
  } else {
    // Handle other errors
  }
  return Promise.reject(error);
});

In this code, we’re using the axios.interceptors.response.use() method to add a response interceptor that checks for specific error codes and handles them accordingly. If the response status is 401, we redirect the user to the login page. If the response status is 404, we handle the error in a custom way. For any other errors, we reject the promise with the error object.

Interceptors as middleware

As we’ve seen, Axios interceptors are a powerful way to modify the behavior of your HTTP requests and responses. By intercepting requests and responses, you can add common functionality to your application without having to repeat the same code in multiple places.

In many ways, interceptors in Axios function similarly to middleware in other web development frameworks. Just like middleware, Axios interceptors provide a way to define custom logic that can be applied to all HTTP requests or responses in your application.

By registering interceptors globally, you can define reusable middleware functions that can be applied to all requests and responses in your application. This can make your code more maintainable and easier to reason about, as you can define your middleware once and use it throughout your application.

Furthermore, by using Axios interceptors, you can separate concerns in your application, making it easier to maintain and extend. You can define interceptors for specific features or modules in your application, allowing you to modify their behavior without affecting the rest of the application.

Overall, Axios interceptors provide a powerful tool that can help you write more maintainable and extensible code by allowing you to define reusable middleware functions that can be applied to all requests and responses in your application.

Conclusion

Axios interceptors are a powerful tool that can be used to implement middleware-style functionality in your web applications. By intercepting requests and responses, you can add common functionality to your application without having to repeat the same code in multiple places.

In this article, we’ve explored how Axios interceptors work and how they can be used to modify HTTP requests and responses. We’ve seen how request interceptors can be used to add common headers or handle authentication tokens, and how response interceptors can be used to handle errors or transform data.

We’ve also seen how interceptors in Axios function similarly to middleware in other web development frameworks, providing a way to define custom logic that can be applied to all requests and responses in your application.

By using Axios interceptors, you can write more maintainable and extensible code that is easier to reason about and separate concerns in your application. Whether you’re building a web application or a Node.js server, Axios interceptors provide a powerful tool for handling HTTP requests and responses.

Apr 1, 2023