Next.js API MiddleWares

Next.js is a popular React framework that allows for server-side rendering of React applications. Next.js provides an API routing system that allows developers to easily create HTTP endpoints within their applications. With the help of middleware, developers can inject additional functionality into the request/response cycle of these API routes. In this article, we’ll explore how to use middleware in Next.js API routes.

What is Middleware?

Middleware is a function that sits between the request and response objects. It can perform a variety of tasks such as logging, authentication, or modifying the response. In the context of Next.js API routes, middleware functions allow developers to modify incoming requests before they get processed or modify the outgoing responses before they are sent back to the client.

Adding Middleware to Next.js API Routes

Adding middleware to Next.js API routes is an easy process. Middleware functions are added to the req and res objects using req.use() and res.use() respectively. Let's take a look at an example of how to use middleware in a Next.js API route:

// pages/api/hello.js

export default function handler(req, res) {
  req.use((req, res, next) => {
    console.log('Incoming Request:', req.url);
    next();
  });

  res.use((req, res) => {
    res.setHeader('X-Powered-By', 'Next.js');
  });

  res.status(200).json({ text: 'Hello' });
}

In this example, we’ve added two middleware functions. The first middleware function logs the incoming request URL to the console. The second middleware function sets a custom response header. Finally, we send a JSON response to the client.

Middleware Order

It is important to note that the order in which middleware is added matters. Middleware functions are processed in the order in which they are added to the request or response object. In the previous example, the req middleware is executed before the res middleware. This means that the response header is set after the incoming request URL is logged to the console.

Conclusion

Middleware functions are a powerful tool that can greatly enhance the functionality of Next.js API routes. They allow developers to inject additional functionality into the request/response cycle. Middleware functions can be used for a variety of tasks such as logging, authentication, or modifying the response. By understanding how middleware works, developers can create powerful and flexible Next.js applications.