next-connect

The promise-based method routing and middleware layer for Next.js (API Routes, Edge API Routes, getServerSideProps, Middleware) and many other frameworks.

Warning v1 is a complete rewrite of v0 and is not backward-compatible. See Releases to learn about the changes.

v0, which is written to be compatible with Express.js middleware, is still maintained with bug fixes. v1 drops explicit support for Express.js middleware, but still provide a way to use them through a wrapper (see below)

Features

• Async middleware
• Lightweight => Suitable for serverless environment
• way faster than Express.js. Compatible with Express.js via a wrapper.
• Works with async handlers (with error catching)
• TypeScript support

Installation

npm install [email protected]

Usage

Note

Although next-connect is initially written for Next.js, it can be used in http server, Vercel. See Examples for more integrations.

Below are some use cases.

Next.js API Routes

// pages/api/hello.js
import type { NextApiRequest, NextApiResponse } from "next";
import { createRouter, expressWrapper } from "next-connect";
import cors from "cors";

// Default Req and Res are IncomingMessage and ServerResponse
// You may want to pass in NextApiRequest and NextApiResponse
const router = createRouter<NextApiRequest, NextApiResponse>();

router
  .use(expressWrapper(cors())) // express middleware are supported if you wrap it with expressWrapper
  .use(async (req, res, next) => {
    const start = Date.now();
    await next(); // call next in chain
    const end = Date.now();
    console.log(`Request took ${end - start}ms`);
  })
  .get((req, res) => {
    res.send("Hello world");
  })
  .post(async (req, res) => {
    // use async/await
    const user = await insertUser(req.body.user);
    res.json({ user });
  })
  .put(
    async (req, res, next) => {
      // You may want to pass in NextApiRequest & { isLoggedIn: true }
      // in createRouter generics to define this extra property
      if (!req.isLoggedIn) throw new Error("thrown stuff will be caught");
      // go to the next in chain
      return next();
    },
    async (req, res) => {
      const user = await updateUser(req.body.user);
      res.json({ user });
    }
  );

// create a handler from router with custom
// onError and onNoMatch
export default router.handler({
  onError: (err, req, res) => {
    console.error(err.stack);
    res.status(500).end("Something broke!");
  },
  onNoMatch: (req, res) => {
    res.status(404).end("Page is not found");
  },
});

Next.js getServerSideProps

// page/users/[id].js
import { createRouter } from "next-connect";

export default function Page({ user, updated }) {
  return (
    <div>
      {updated && <p>User has been updated</p>}
      <div>{JSON.stringify(user)}</div>
      <form method="POST">{/* User update form */}</form>
    </div>
  );
}

const router = createRouter()
  .use(async (req, res, next) => {
    // this serve as the error handling middleware
    try {
      return await next();
    } catch (e) {
      return {
        props: { error: e.message },
      };
    }
  })
  .use(async (req, res, next) => {
    logRequest(req);
    return next();
  })
  .get(async (req, res) => {
    const user = await getUser(req.params.id);
    if (!user) {
      // https://nextjs.org/docs/api-reference/data-fetching/get-server-side-props#notfound
      return { props: { notFound: true } };
    }
    return { props: { user } };
  })
  .post(async (req, res) => {
    const user = await updateUser(req);
    return { props: { user, updated: true } };
  });

export async function getServerSideProps({ req, res }) {
  return router.run(req, res);
}

Next.js Edge API Routes (Beta)

Edge Router can be used in Edge Runtime

import type { NextFetchEvent, NextRequest } from "next/server";
import { createEdgeRouter } from "next-connect";
import cors from "cors";

// Default Req and Evt are Request and unknown
// You may want to pass in NextRequest and NextFetchEvent
const router = createEdgeRouter<NextRequest, NextFetchEvent>();

router
  .use(expressWrapper(cors())) // express middleware are supported if you wrap it with expressWrapper
  .use(async (req, evt, next) => {
    const start = Date.now();
    await next(); // call next in chain
    const end = Date.now();
    console.log(`Request took ${end - start}ms`);
  })
  .get((req, res) => {
    return new Response("Hello world");
  })
  .post(async (req, res) => {
    // use async/await
    const user = await insertUser(req.body.user);
    res.json({ user });
    return new Response(JSON.stringify({ user }), {
      status: 200,
      headers: {
        "content-type": "application/json",
      },
    });
  })
  .put(async (req, res) => {
    const user = await updateUser(req.body.user);
    return new Response(JSON.stringify({ user }), {
      status: 200,
      headers: {
        "content-type": "application/json",
      },
    });
  });

// create a handler from router with custom
// onError and onNoMatch
export default router.handler({
  onError: (err, req, evt) => {
    console.error(err.stack);
    return new NextResponse("Something broke!", {
      status: 500,
    });
  },
  onNoMatch: (req, res) => {
    return new NextResponse("Page is not found", {
      status: 404,
    });
  },
});

Next.js Middleware

Edge Router can be used in Next.js Middleware

// middleware.ts
import { NextResponse } from "next/server";
import type { NextRequest, NextFetchEvent } from "next/server";
import { createEdgeRouter } from "next-connect";

// This function can be marked `async` if using `await` inside

const router = createEdgeRouter<NextRequest, NextFetchEvent>();

router.use(async (request, _, next) => {
  await logRequest(request);
  return next();
});

router.get("/about", (request) => {
  return NextResponse.redirect(new URL("/about-2", request.url));
});

router.use("/dashboard", (request) => {
  if (!isAuthenticated(request)) {
    return NextResponse.redirect(new URL("/login", request.url));
  }
  return NextResponse.next();
});

router.all((request) => {
  // default if none of the above matches
  return NextResponse.next();
});

export function middleware(request: NextRequest) {
  return NextResponse.redirect(new URL("/about-2", request.url));
}

API

The following APIs are rewritten in term of NodeRouter (createRouter), but they apply to EdgeRouter (createEdgeRouter) as well.

router = createRouter()

Create an instance Node.js router.

router.use(base, ...fn)

base (optional) - match all routes to the right of base or match all if omitted. (Note: If used in Next.js, this is often omitted)

fn(s) can either be:

• functions of (req, res[, next])
• or a router instance

// Mount a middleware function
router1.use(async (req, res, next) => {
  req.hello = "world";
  await next(); // call to proceed to the next in chain
  console.log("request is done"); // call after all downstream handler has run
});

// Or include a base
router2.use("/foo", fn); // Only run in /foo/**

// mount an instance of router
const sub1 = createRouter().use(fn1, fn2);
const sub2 = createRouter().use("/dashboard", auth);
const sub3 = createRouter()
  .use("/waldo", subby)
  .get(getty)
  .post("/baz", posty)
  .put("/", putty);
router3
  // - fn1 and fn2 always run
  // - auth runs only on /dashboard
  .use(sub1, sub2)
  // `subby` runs on ANY /foo/waldo?/*
  // `getty` runs on GET /foo/*
  // `posty` runs on POST /foo/baz
  // `putty` runs on PUT /foo
  .use("/foo", sub3);

router.METHOD(pattern, ...fns)

METHOD is an HTTP method (GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE) in lowercase.

pattern (optional) - match routes based on supported pattern or match any if omitted.

fn(s) are functions of (req, res[, next]).

router.get("/api/user", (req, res, next) => {
  res.json(req.user);
});
router.post("/api/users", (req, res, next) => {
  res.end("User created");
});
router.put("/api/user/:id", (req, res, next) => {
  // https://nextjs.org/docs/routing/dynamic-routes
  res.end(`User ${req.params.id} updated`);
});

// Next.js already handles routing (including dynamic routes), we often
// omit `pattern` in `.METHOD`
router.get((req, res, next) => {
  res.end("This matches whatever route");
});

Note You should understand Next.js file-system based routing. For example, having a router.put("/api/foo", handler) inside page/api/index.js does not serve that handler at /api/foo.

router.all(pattern, ...fns)

Same as .METHOD but accepts any methods.

router.handler(options)

Create a handler to handle incoming requests.

options.onError

Accepts a function as a catch-all error handler; executed whenever a handler throws an error. By default, it responds with a generic 500 Internal Server Error while logging the error to console.

function onError(err, req, res) {
  logger.log(err);
  // OR: console.error(err);

  res.status(500).end("Internal server error");
}

export default router.handler({ onError });

options.onNoMatch

Accepts a function of (req, res) as a handler when no route is matched. By default, it responds with a 404 status and a Route [Method] [Url] not found body.

function onNoMatch(req, res) {
  res.status(404).end("page is not found... or is it!?");
}

export default router.handler({ onNoMatch });

router.run(req, res)

Runs req and res through the middleware chain and returns a promise. It resolves with the value returned from handlers.

router
  .use(async (req, res, next) => {
    return (await next()) + 1;
  })
  .use(async () => {
    return (await next()) + 2;
  })
  .use(async () => {
    return 3;
  });

console.log(await router.run(req, res));
// The above will print "6"

If an error in thrown within the chain, router.run will reject. You can also add a try-catch in the first middleware to catch the error before it rejects the .run() call:

router
  .use(async (req, res, next) => {
    return next().catch(errorHandler);
  })
  .use(thisMiddlewareMightThrow);

await router.run(req, res);

Common errors

There are some pitfalls in using next-connect. Below are things to keep in mind to use it correctly.

1. Always await next()

If next() is not awaited, errors will not be caught if they are thrown in async handlers, leading to UnhandledPromiseRejection.

// OK: we don't use async so no need to await
router
  .use((req, res, next) => {
    next();
  })
  .use((req, res, next) => {
    next();
  })
  .use(() => {
    throw new Error("");
  });

// BAD: This will lead to UnhandledPromiseRejection
router
  .use(async (req, res, next) => {
    next();
  })
  .use(async (req, res, next) => {
    next();
  })
  .use(async () => {
    throw new Error("");
  });

// GOOD
router
  .use(async (req, res, next) => {
    await next(); // next() is awaited, so errors are caught properly
  })
  .use((req, res, next) => {
    return next(); // this works as well since we forward the rejected promise
  })
  .use(async () => {
    throw new Error("");
    // return new Promise.reject("");
  });

Another issue is that the handler would resolve before all the code in each layer runs.

const handler = router
  .use(async (req, res, next) => {
    next(); // this is not returned or await
  })
  .get(async () => {
    // simulate a long task
    await new Promise((resolve) => setTimeout(resolve, 1000));
    res.send("ok");
    console.log("request is completed");
  })
  .handler();

await handler(req, res);
console.log("finally"); // this will run before the get layer gets to finish

// This will result in:
// 1) "finally"
// 2) "request is completed"

2. DO NOT reuse the same instance of router like the below pattern:

// api-libs/base.js
export default createRouter().use(a).use(b);

// api/foo.js
import router from "api-libs/base";
export default router.get(x).handler();

// api/bar.js
import router from "api-libs/base";
export default router.get(y).handler();

This is because, in each API Route, the same router instance is mutated, leading to undefined behaviors. If you want to achieve something like that, you can use router.clone to return different instances with the same routes populated.

// api-libs/base.js
export default createRouter().use(a).use(b);

// api/foo.js
import router from "api-libs/base";
export default router.clone().get(x).handler();

// api/bar.js
import router from "api-libs/base";
export default router.clone().get(y).handler();

3. DO NOT use response function like res.(s)end or res.redirect inside getServerSideProps.

// page/index.js
const handler = createRouter()
  .use((req, res) => {
    // BAD: res.redirect is not a function (not defined in `getServerSideProps`)
    // See https://github.com/hoangvvo/next-connect/issues/194#issuecomment-1172961741 for a solution
    res.redirect("foo");
  })
  .use((req, res) => {
    // BAD: `getServerSideProps` gives undefined behavior if we try to send a response
    res.end("bar");
  });

export async function getServerSideProps({ req, res }) {
  await router.run(req, res);
  return {
    props: {},
  };
}

3. DO NOT use handler() directly in getServerSideProps.

// page/index.js
const router = createRouter().use(foo).use(bar);
const handler = router.handler();

export async function getServerSideProps({ req, res }) {
  await handler(req, res); // BAD: You should call router.run(req, res);
  return {
    props: {},
  };
}

Recipes

Next.js

// pages/api/[[...slug]].js
import { createRouter } from "next-connect";

const router = createRouter()
  .use("/api/hello", someMiddleware())
  .get("/api/user/:userId", (req, res) => {
    res.send(`Hello ${req.params.userId}`);
  });

export default router.handler();

Express.js Compatibility

import { expressWrapper } from "next-connect";
import someExpressMiddleware from "some-express-middleware";

router.use(expressWrapper(someExpressMiddleware));

Contributing

Please see my contributing.md.

License

MIT