A middleware composition library for Next.js applications that allows you to organize and chain middleware functions based on URL patterns.

npm install @rescale/nemo

pnpm add @rescale/nemo

bun add @rescale/nemo

• Path-based middleware routing
• Global middleware support (before/after)
• Context sharing between middleware
• Support for both legacy and modern middleware patterns
• Request/Response header and cookie forwarding

Can be either a legacy Next.js middleware (NextMiddleware) or the new middleware format (NewMiddleware).

Record<string, MiddlewareFunction | MiddlewareFunction[]>

interface MiddlewareFunctionProps {
  request: NextRequest;
  context: MiddlewareContext;
  event: NextFetchEvent;
  forward: (response: MiddlewareReturn) => void;
}

function createMiddleware(
  pathMiddlewareMap: MiddlewareConfig,
  globalMiddleware?: {
    before?: MiddlewareFunction | MiddlewareFunction[];
    after?: MiddlewareFunction | MiddlewareFunction[];
  }
): NextMiddleware

Creates a composed middleware function that:

• Executes global "before" middleware first
• Matches URL patterns and executes corresponding middleware
• Executes global "after" middleware last
• Forwards headers and cookies between middleware functions

function forward(response: MiddlewareReturn): void

Function that allows passing response from legacy middleware functions to the next middleware in the chain. This enables compatibility between legacy Next.js middleware and the new middleware format.

import { createMiddleware } from '@rescale/nemo';

export default createMiddleware({
  '/api/:path': async ({ request }) => {
    // Handle API routes
  },
  '/protected/:path': async ({ request, context }) => {
    // Handle protected routes
  }
});

import { createMiddleware } from '@rescale/nemo';

export default createMiddleware({
  '/api/:path': apiMiddleware,
},
{
  before: [loggerMiddleware, authMiddleware],
  after: cleanupMiddleware,
});

import { createMiddleware } from '@rescale/nemo';

export default createMiddleware({
  '/:path': [
    async ({ context }) => {
      context.set('user', { id: 1 });
    },
    async ({ context }) => {
      const user = context.get('user');
      // Use the user data
    }
  ]
});

• Middleware functions are executed in order until a Response is returned
• The context Map is shared between all middleware functions in the chain
• Headers and cookies are automatically forwarded between middleware functions
• Supports both Next.js legacy middleware pattern and the new props-based pattern

I'm working with Next.js project for a few years now, after Vercel moved multiple /**/_middleware.ts files to a single /middleware.ts file, there was a unfilled gap - but just for now. After a 2023 retro I had found that there is no good solution for that problem, so I took matters into my own hands. I wanted to share that motivation with everyone here, as I think that we all need to remember how it all started.

Hope it will save you some time and would make your project DX better!