router-middleware

6.1.6 verified Sat Apr 25 auth: no javascript

An Express-style router for Node.js with full TypeScript safety, including inferred route params from path strings (e.g., '/user/:id' gives req.params.id: string) and typed request/response bodies via generic parameters. Current stable version is 6.1.6. Key differentiators: no view engine, no global state, dual ESM/CJS exports, built-in error handling, and safe defaults (1 MB JSON limit, strict content-type checks). Released actively with regular updates; ships its own TypeScript types.

Common errors

error TypeError: app is not a function ↓

cause Incorrect import: using require('router-middleware') without .default in CJS

fix

Change to const app = require('router-middleware').default;

error Type '{}' is not assignable to type 'string' ↓

cause Using res.send() with an object instead of res.json()

fix

Replace res.send(obj) with res.json(obj)

error Cannot find name 'app'. ↓

cause Missing app.jsonParser() call or forgot to call createApp()

fix

Ensure const app = createApp(); is called and app.use(app.jsonParser()); is added

error Property 'params' does not exist on type 'Request' ↓

cause Route handler not using generic parameter for path, so params is not typed

fix

Add generic type like app.get<'/path/:id'>('/path/:id', handler) to infer params

Warnings

breaking Default export is ESM-only; CJS require must use .default ↓

fix Use `const app = require('router-middleware').default;` instead of `const app = require('router-middleware');`

breaking Changed from `req.param` to `req.params` for route parameters ↓

fix Replace `req.param('id')` with `req.params.id`

gotcha JSON body parser is not automatic; must be explicitly added with app.use(app.jsonParser()) ↓

fix Add `app.use(app.jsonParser());` before routes that expect JSON body

gotcha res.send() does NOT accept objects; use res.json() for objects ↓

fix Use `res.json({...})` instead of `res.send({...})`

deprecated app.useError() has been renamed to app.onError() in latest v7 beta ↓

fix Migrate to `app.onError(handler)` when upgrading to v7

Install

npm install router-middleware

yarn add router-middleware

pnpm add router-middleware

Imports

default (createApp)
wrong
```
const createApp = require('router-middleware');
```
correct
```
import createApp from 'router-middleware';
```
ESM default export. CommonJS users must use `require('router-middleware').default`.

Router

wrong

const { Router } = require('router-middleware');

correct

import { Router } from 'router-middleware';

Named export available for both ESM and CJS.

default (require)

wrong

const createApp = require('router-middleware');

correct

const createApp = require('router-middleware').default;

CommonJS requires explicit `.default` due to ESM-first package.

Quickstart

Creates a typed HTTP server with route param inference and typed request/response bodies.

import http from 'node:http';
import createApp from 'router-middleware';

const app = createApp();
const server = http.createServer(app);

app.use(app.jsonParser());

app.get<'/user/:id'>('/user/:id', (req, res) => {
  res.json({ id: req.params.id });
});

app.post<'/user/:id/email', { email: string }, { ok: true; id: string; email: string }>(
  '/user/:id/email',
  (req, res) => {
    res.status(201).json({
      ok: true,
      id: req.params.id,
      email: req.body.email,
    });
  }
);

app.get<'/health'>('/health', (_req, res) => {
  res.status(200).send('OK');
});

app.useError((err, _req, res, _next) => {
  res.status(err?.statusCode ?? 500).json({ error: err?.message ?? 'error' });
});

server.listen(5150);