Functions

This package introduces middleware functions standardization for more elastic approach to development and feature delivery.

Function schema

This example shows all props that are provided for your usage.

_middleware.ts

async ({ request, response, context, event, forward, params }: MiddlewareFunctionProps) => {
  // function body
}

That's a user middleware's request passed to function, which cookies (and only them) can be later updated by forwarded functions in chain.

This props cookies will only deffer from the original user's request if you've forwarded any response it in the chain.

Type: NextResponse | undefined

This property contains (optional) resposne object that were forwarded in prev middleware function using forward() function.

Learn more about Forward functions in middleware

It can be used for example for checking custom headers from external packages middlewares output that was forwarded in chain.

_middleware.ts

async ({ response }: MiddlewareFunctionProps) => {
  if (response) {
    console.log(response.headers.get('x-custom-header'));
  }
}

If forwarded middleware added any custom headers or cookies, they will be passed to user at the end of the chain no matter if you handled that.

This property contains context shared across whole execution chain for every function.

Learn more about Shared Context in middleware

If you want to know more about Map interface usage please refer to these docs.

This property contains event object for serverless functions execution.

It can be used to use Next.js 15 new features like event.waitUntil().

You can read more there: Next.js 15 waitUntil

_middleware.ts

// Example URL: /team/123
// Matcher: '/team/:slug'
 
async ({ params }: MiddlewareFunctionProps) => {
  console.log(params().slug); // Output: 123
}