Next.js Intercepting Routes

Introduction

In Next.js, you can use middleware to intercept routes before they are rendered. This can be useful for authentication, loading state, and more. In this guide, we'll explore how to use middleware in Next.js to intercept routes.

Syntax

Create a new file in the pages directory called _middleware.js:

export default (req, res, next) => {
  // middleware logic here
  next()
}

Example

In this example, we'll create a middleware that logs the URL of each request.

// _middleware.js

export default (req, res, next) => {
  console.log(`Request URL: ${req.url}`)
  next()
}

Explanation

In Next.js, middleware is just a function that receives the req, res, and next parameters. req is the request object, res is the response object, and next is a function that calls the next middleware or the route handler.

Middleware functions can run asynchronous code, like database queries or network requests, before calling next. This can be useful for loading data for a specific route before it is rendered.

Use

Middleware can be used for a wide variety of purposes in Next.js. Here are a few common use cases:

• Authentication: Check if the user is logged in before rendering a route.
• Caching: Load data from a cache instead of making a new request for each page load.
• Loading state: Show a loading indicator while loading page data.
• Logging: Log requests for debugging purposes.

Important Points

• Middleware functions are executed in the order they are defined.
• Middleware can be added to a specific route or to all routes using the getInitialProps function.
• Middleware can be used to modify the req or res objects, or to send a response early using res.send.

Summary

Next.js middleware is a powerful tool that can be used for a variety of purposes, including authentication, caching, and logging. By intercepting routes, middleware can modify the request or response, or load data before it is rendered.