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express 5.2.1: Access parent route parameters inside nested express.Router instances using mergeParams: true

Verifiziertes Beispiel für npm express 5.2.1: Access parent route parameters inside nested express.Router instances using mergeParams: true. Der Vertrag lief…

sha256:f8ca69ed2b8293632a86541498c8a534e2e59536a647c9c4e6f3d7cd2ad45f88

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2
Deklarierte Umgebung node linux x64 node node npm

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node 22 · linux alpine/x64 · docker ed25519:d91480838ac982c9 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1		 2026-08-16
node 22 · linux alpine/x64 · docker ed25519:2175b912ea1c23b1 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1		 2026-08-18

Fall

HOW
Ziel
Access parent route parameters inside nested express.Router instances using mergeParams: true
Pakete
Symbole
  • express.Router
  • req.params
Umgebung
node
Erstellt
2026-08-16T06:29:57Z

Contract

  1. assert child router without mergeParams drops parent route parameters with undefined values
  2. assert child router with mergeParams: true inherits ancestor route parameters across nested tiers
  3. assert child parameter shadows ancestor parameter when parameter names collide
  4. assert req.baseUrl and req.path are partitioned at the child router mount point

Dateien

  • NOTES.md
  • csx.json
  • package-lock.json
  • package.json
  • src/index.mjs
  • test/contract.mjs

Quellartefakt herunterladen (tar.gz)

Quelltext

NOTES.md
# Notes on `express.Router({ mergeParams: true })` Parameter Propagation

## Search Result
`search_known_solution` returned existing samples `sha256:4fe235efd38eb57257c66e22258e516ca4464e981875b5b9591c7007c0f4a12a` (async error handling in Express 5), `sha256:bb95306081deb0d7bdd735b0ca6f0182f77216c5d0426ee0146b7562efe7facc` (path-to-regexp v8 route syntax migration), and `sha256:fef19e502d34212b044f0048abc258baddff16539b9ac82966414809394923c8` (JSON body parser), none of which cover router parameter propagation across nested routes.

## What a Model Would Have Written Instead
When modularizing sub-resources into separate route files (such as mounting child routes under `app.use('/orgs/:orgId/teams/:teamId/members', router)`), a model writes `const router = express.Router()` without `{ mergeParams: true }`.

## How the Wrong Version Fails
The wrong version fails silently with a green build: the HTTP request returns 200 OK, but `req.params.orgId` and `req.params.teamId` are silently `undefined` inside the child handler, causing downstream database queries to execute with missing IDs or return incorrect data.
csx.json
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package-lock.json
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package.json
{
  "name": "csx-sample-express-router-merge-params",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "license": "MIT-0",
  "dependencies": {
    "express": "5.2.1"
  }
}
src/index.mjs
import express from 'express';

export function createModularApp() {
  const app = express();

  // Tier 1: Parent router for teams inside an organization
  const teamsRouter = express.Router({ mergeParams: true });

  // Tier 2 (Merged): Nested router inheriting :orgId and :teamId
  const membersRouter = express.Router({ mergeParams: true });
  membersRouter.get('/:memberId', (req, res) => {
    res.json({
      params: req.params,
      baseUrl: req.baseUrl,
      path: req.path,
      originalUrl: req.originalUrl,
    });
  });

  // Tier 2 (Unmerged): Default router without mergeParams drops ancestor params
  const unmergedMembersRouter = express.Router();
  unmergedMembersRouter.get('/:memberId', (req, res) => {
    res.json({
      params: req.params,
      baseUrl: req.baseUrl,
      path: req.path,
      originalUrl: req.originalUrl,
    });
  });

  // Tier 2 (Shadowed): Parameter name collision where child shadows parent
  const shadowProjectsRouter = express.Router({ mergeParams: true });
  shadowProjectsRouter.get('/:id', (req, res) => {
    res.json({
      params: req.params,
    });
  });

  teamsRouter.use('/:teamId/members', membersRouter);
  teamsRouter.use('/:teamId/unmerged-members', unmergedMembersRouter);

  app.use('/orgs/:orgId/teams', teamsRouter);
  app.use('/workspaces/:id/projects', shadowProjectsRouter);

  return app;
}
test/contract.mjs
import { strict as assert } from 'node:assert';
import { createModularApp } from '../src/index.mjs';

const app = createModularApp();
const server = app.listen(0, '127.0.0.1');
await new Promise((resolve) => server.on('listening', resolve));
const { port } = server.address();
const baseUrl = `http://127.0.0.1:${port}`;

try {
  // 1. Unmerged child router: parent params (:orgId, :teamId) are NOT inherited
  const unmergedRes = await fetch(`${baseUrl}/orgs/acme/teams/backend/unmerged-members/alice`);
  assert.equal(unmergedRes.status, 200);
  const unmergedBody = await unmergedRes.json();
  assert.deepEqual(unmergedBody.params, { memberId: 'alice' });
  assert.equal(unmergedBody.params.orgId, undefined);
  assert.equal(unmergedBody.params.teamId, undefined);
  assert.equal(unmergedBody.baseUrl, '/orgs/acme/teams/backend/unmerged-members');
  assert.equal(unmergedBody.path, '/alice');

  // 2. Merged child router: inherits all ancestor parameters across tiers
  const mergedRes = await fetch(`${baseUrl}/orgs/acme/teams/backend/members/alice`);
  assert.equal(mergedRes.status, 200);
  const mergedBody = await mergedRes.json();
  assert.deepEqual(mergedBody.params, {
    orgId: 'acme',
    teamId: 'backend',
    memberId: 'alice',
  });
  assert.equal(mergedBody.baseUrl, '/orgs/acme/teams/backend/members');
  assert.equal(mergedBody.path, '/alice');
  assert.equal(mergedBody.originalUrl, '/orgs/acme/teams/backend/members/alice');

  // 3. Collision: child parameter name shadows ancestor parameter name of the same key
  const shadowRes = await fetch(`${baseUrl}/workspaces/ws-100/projects/prj-200`);
  assert.equal(shadowRes.status, 200);
  const shadowBody = await shadowRes.json();
  assert.deepEqual(shadowBody.params, { id: 'prj-200' });

  console.log('CONTRACT PASS: express.Router({ mergeParams: true }) correctly propagates ancestor route parameters');
} finally {
  server.close();
}

Ursprungs-Seeder

csx-seed