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Edge Middleware runs on the Edge Runtime, a runtime built on top of the V8 JavaScript engine. The Edge Runtime provides a subset of Web APIs for you to use when creating Middleware. This lightweight API layer is built to be performant and execute code with minimal latency. When writing Middleware, you can use any of the supported APIs from the Edge Runtime.

To add Middleware to your app, you need to create a middleware.ts or middleware.js file at the same level as your app or pages directory (even if you're using a src directory):

The Middleware function must be a default export as shown below:

middleware.ts
export default function customName() {}

Middleware will be invoked for every route in your project. If you only want it to be run on specific paths, you can define those either with a custom matcher config or with conditional statements.

While the config option is the preferred method, as it does not get invoked on every request, you can also use conditional statements to only run the Middleware when it matches specific paths.

To decide which route the Middleware should be run on, you can use a custom matcher config to filter on specific paths. The matcher property can be used to define either a single path, or using an array syntax for multiple paths.

Edge Middleware runs on every request by default. To run on specific paths instead, use the matcher property of the Middleware config object. Even when using path matching, Edge Middleware runs on all /_next/data/ requests for getServerSideProps and getStaticProps pages for the sake of consistency. For more information, review our docs on Edge Middleware API as well as the Next.js matcher docs.
middleware.ts
export const config = {
  matcher: '/about/:path*',
};
middleware.ts
export const config = {
  matcher: ['/about/:path*', '/dashboard/:path*'],
};

The matcher config has full regex support for cases such as negative lookaheads or character matching.

To match all request paths except for the ones starting with:

  • api (API routes)
  • _next/static (static files)
  • favicon.ico (favicon file)
middleware.ts
export const config = {
  matcher: ['/((?!api|_next/static|favicon.ico).*)'],
};

To match /blog/123 but not /blog/abc:

middleware.ts
export const config = {
  matcher: ['/blog/:slug(\\d{1,})'],
};

For help on writing your own regex path matcher, review Path to regexp.

middleware.ts
import { rewrite } from '@vercel/edge';
 
export default function middleware(request: Request) {
  const url = new URL(request.url);
 
  if (url.pathname.startsWith('/about')) {
    return rewrite(new URL('/about-2', request.url));
  }
 
  if (url.pathname.startsWith('/dashboard')) {
    return rewrite(new URL('/dashboard/user', request.url));
  }
}

See the @vercel/edge documentation for more information on using the @vercel/edge package.

Property
Type
Description
matcher
string / string[]
A string or array of strings that define the paths the Middleware should be run on

The Edge Middleware signature is made up of two parameters: request and context. The request parameter is an instance of the Request object, and the context parameter is an object containing the waitUntil method. Both parameters are optional.

Parameter
Description
Next.js (/app) or (/pages)
Other Frameworks
request
An instance of the Request object
context
An extension to the standard Request object

Next.js Middleware comes with built in helpers that are based upon the native FetchEvent, Response, and Request objects.

See the next/server documentation for more information.

Next.js (/app)
Next.js (/pages)
Other frameworks
middleware.ts
// config with custom matcher
export const config = {
  matcher: '/about/:path*',
};
 
export default function middleware(request: Request) {
  return Response.redirect(new URL('/about-2', request.url));
}

The Request object represents an HTTP request. It is a wrapper around the Fetch API Request object. When using TypeScript, you do not need to import the Request object, as it is already available in the global scope.

Property
Type
Description
url
string
The URL of the request
method
string
The HTTP method of the request
headers
Headers
The headers of the request
body
The body of the request
bodyUsed
boolean
Whether the body has been read
cache
string
The cache mode of the request
credentials
string
The credentials mode of the request
destination
string
The destination of the request
integrity
string
The integrity of the request
redirect
string
The redirect mode of the request
referrer
string
The referrer of the request
referrerPolicy
string
The referrer policy of the request
mode
string
The mode of the request
signal
The signal of the request
arrayBuffer
function
Returns a promise that resolves with an ArrayBuffer
blob
function
Returns a promise that resolves with a Blob
formData
function
Returns a promise that resolves with a FormData
json
function
Returns a promise that resolves with a JSON object
text
function
Returns a promise that resolves with a string
clone
function
Returns a clone of the request

To learn more about the NextRequest object and its properties, visit the Next.js documentation.

The waitUntil() method is from the ExtendableEvent interface. It accepts a Promise as an argument, which will keep the function running until the Promise resolves.

It can be used to keep the function running after a response has been sent. This is useful when you have an async task that you want to keep running after returning a response.

The example below will send a response immediately, but will keep the function running for ten seconds, fetch a product and log it to the console.

Next.js (/app)
Next.js (/pages)
Other frameworks
middleware.ts
import type { NextFetchEvent } from 'next/server';
 
export const config = {
  matcher: '/',
};
 
const wait = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));
 
async function getProduct() {
  const res = await fetch('https://api.vercel.app/products/1');
  await wait(10000);
  return res.json();
}
 
export default function middleware(request: Request, context: NextFetchEvent) {
  context.waitUntil(getProduct().then((json) => console.log({ json })));
 
  return new Response(JSON.stringify({ hello: 'world' }), {
    status: 200,
    headers: { 'content-type': 'application/json' },
  });
}
Property
Type
Description
(promise: Promise<unknown>): void
Prolongs the execution of the function until the promise passed to waitUntil is resolved
Last updated on March 2, 2023