Middleware API

Reference

Edge Middleware API Reference

Learn about the Edge runtime and available APIs when working with Edge Middleware. Supported APIs include Network, Encoding, and Web Stream APIs.

Table of Contents

Next.js (/app)

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.

Edge Middleware setup

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):

middleware.ts
package.json

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

middleware.ts

export default function customName() {}

`config` object

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.

Match paths based on custom matcher config

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.

Match a single path

middleware.ts

export const config = {
  matcher: '/about/:path*',
};

Match multiple paths

middleware.ts

export const config = {
  matcher: ['/about/:path*', '/dashboard/:path*'],
};

Match using regex

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

Match based on a negative lookahead

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).*)'],
};

Match based on character matching

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.

Match paths based on conditional statements

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 Helper Methods below for more information on using the @vercel/edge package.

`config` properties

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

Edge Middleware signature

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	`Request` or `NextRequest`	`Request`
`context`	An extension to the standard `Request` object	`NextFetchEvent`	`RequestContext`

Edge Middleware comes with built in helpers that are based on the native FetchEvent, Response, and Request objects.

See the section on helpers below 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));
}

If you're not using a framework, you must either add "type": "module" to your package.json or change your JavaScript Functions' file extensions from .js to .mjs

Request

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.

Request Properties

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`	`ReadableStream`	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`	`AbortSignal`	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.

`waitUntil()`

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
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' },
  });
}

If you're not using a framework, you must either add "type": "module" to your package.json or change your JavaScript Functions' file extensions from .js to .mjs

Context properties

Property	Type	Description
`waitUntil`	`(promise: Promise<unknown>): void`	Prolongs the execution of the function until the promise passed to `waitUntil` is resolved

Middleware helper methods

You can use Vercel-specific helper methods to access a request's geolocation, IP Address, and more when deploying Edge Middleware on Vercel.

You can access these helper methods with the request and response objects in your middleware handler method.

These helpers are exclusive to Vercel, and will not work on other providers, even if your app is built with Next.js.

Geolocation

This helper is also available in Edge Functions .

The geo helper object returns geolocation information for the incoming request. It has the following properties:

Property	Description
`city`	The city that the request originated from
`country`	The country that the request originated from
`latitude`	The latitude of the client
`longitude`	The longitude of the client
`region`	The Edge Network region that received the request

Each property returns a string, or undefined.

Next.js (/app)

Next.js (/pages)

Other frameworks

middleware.ts

import { NextResponse } from 'next/server';
import type { NextRequest } from 'next/server';
 
// The country to block from accessing the secret page
const BLOCKED_COUNTRY = 'SE';
 
// Trigger this middleware to run on the `/secret-page` route
export const config = {
  matcher: '/secret-page',
};
 
export function middleware(request: NextRequest) {
  // Extract country. Default to US if not found.
  const country = (request.geo && request.geo.country) || 'US';
 
  console.log(`Visitor from ${country}`);
 
  // Specify the correct route based on the requests location
  if (country === BLOCKED_COUNTRY) {
    request.nextUrl.pathname = '/login';
  } else {
    request.nextUrl.pathname = `/secret-page`;
  }
 
  // Rewrite to URL
  return NextResponse.rewrite(request.nextUrl);
}

IP Address

This helper is also available in Edge Functions .

The ip object returns the IP address of the request from the headers, or undefined.

middleware.ts

import { ipAddress } from '@vercel/functions';
import { next } from '@vercel/edge';
 
export default function middleware(request: Request) {
  const ip = ipAddress(request);
  return next({
    headers: { 'x-your-ip-address': ip || 'unknown' },
  });
}

`RequestContext`

This helper is also available in Edge Functions .

The RequestContext is an extension of the standard Request object, which contains the waitUntil function. The following example works in middleware for all frameworks:

middleware.ts

import type { RequestContext } from '@vercel/edge';
 
export default function handler(request: Request, context: RequestContext) {
  context.waitUntil(getAlbum().then((json) => console.log({ json })));
 
  return new Response(`Hello there, from ${request.url} I'm an Edge Function!`);
}
 
export const config = {
  matcher: '/',
};
 
const wait = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));
 
async function getAlbum() {
  const res = await fetch('https://jsonplaceholder.typicode.com/albums/1');
  await wait(10000);
  return res.json();
}

Rewrites

This helper is only available in Edge Middleware.

The NextResponse.rewrite() helper returns a response that rewrites the request to a different URL.

Next.js (/app)

Next.js (/pages)

Other frameworks

middleware.ts

import { NextResponse } from 'next/server';
import type { NextRequest } from 'next/server';
// Trigger this middleware to run on the `/about` route
export const config = {
  matcher: '/about',
};
 
export function middleware(request: NextRequest) {
  // Rewrite to URL
  return NextResponse.rewrite('/about-2');
}

Continuing the middleware chain

This helper is only available in Edge Middleware.

The NextResponse.next() helper returns a Response that instructs the function to continue the middleware chain. It takes the following optional parameters:

Parameter	type	Description
`headers`	`Headers[]` or `Headers`	The headers you want to set
`status`	`number`	The status code
`statusText`	`string`	The status text

The following example adds a custom header, then continues the middleware chain:

Next.js (/app)

Next.js (/pages)

Other frameworks

middleware.ts

import { NextResponse } from 'next/server';
export default function middleware() {
  return NextResponse.next({
    headers: { 'x-from-middleware': 'true' },
  });
}

`next()` no-op example

This no-op example will return a 200 OK response with no further action:

Next.js (/app)

Next.js (/pages)

Other frameworks

middleware.ts

import { NextResponse } from 'next/server';
export default function middleware() {
  return NextResponse.next();
}

Last updated on July 16, 2024

Quickstart

Edge Runtime

Was this helpful?