Compile error "app.router is deprecated" after upgrading from 11.0.7 to 11.0.8

[bhalperin]

Did you read the migration guide?

• I have read the whole migration guide

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Potential Commit/PR that introduced the regression

No response

NestJS version

11.0.7 -> 11.0.8

Describe the regression

No changes in my code that compiled successfully prior to updating nestjs to 11.0.8.
Full stack trace:

C:\data\projects\nx\github\node_modules\express\lib\application.js:131
      throw new Error('\'app.router\' is deprecated!\nPlease see the 3.x to 4.x migration guide for details on how to update your app.');
            ^
Error: 'app.router' is deprecated!
Please see the 3.x to 4.x migration guide for details on how to update your app.
    at Function.get (C:\data\projects\nx\github\node_modules\express\lib\application.js:131:13)
    at ExpressAdapter.isMiddlewareApplied (C:\data\projects\nx\github\node_modules\@nestjs\platform-express\adapters\express-adapter.js:332:19)
    at C:\data\projects\nx\github\node_modules\@nestjs\platform-express\adapters\express-adapter.js:192:37
    at Array.filter (<anonymous>)
    at ExpressAdapter.registerParserMiddleware (C:\data\projects\nx\github\node_modules\@nestjs\platform-express\adapters\express-adapter.js:192:14)
    at NestApplication.registerParserMiddleware (C:\data\projects\nx\github\node_modules\@nestjs\core\nest-application.js:110:26)
    at NestApplication.init (C:\data\projects\nx\github\node_modules\@nestjs\core\nest-application.js:97:31)
    at NestApplication.listen (C:\data\projects\nx\github\node_modules\@nestjs\core\nest-application.js:170:13)
    at bootstrap (C:\data\projects\nx\github\dist\apps\api\main.js:1541:5)

Minimum reproduction code

No response

Input code

Expected behavior

Sucessful compilation

Other

No response

[micalevisk]

Please provide a minimum reproduction repository. You can start one by running npm init nest in your terminal

why reproductions are required

[micalevisk]

if this is a bug, it might be related with https://github.com/nestjs/nest/pull/14574/files

@bhalperin can you revert that change locally in your project? or provide a minimum repro

[kamilmysliwiec]

@bhalperin do you have express v4 installed? @nestjs/platform-express v11 requires express v5

[bhalperin]

@kamilmysliwiec @nestjs/platform-express has its own instance of express v5 installed inside its own node_modules and I believe it relies on this instance.
My top level node_modules has another instance of express v4 (don't know what other package installs it). But it was not an issue with nestjs v11.0.7 or less. And my code has not changed a bit.
I reinstalled all packages (yarn install).

Here is my full top package.json (it's a NX project) all with the latest:

{
	"name": "@github/source",
	"version": "0.0.3",
	"license": "MIT",
	"scripts": {
		"serve:api": "nx run api:serve --watch=true",
		"serve:ui": "nx run ui:serve --verbose=true",
		"lint:api": "yarn nx run api:lint",
		"build:api": "yarn nx run api:build",
		"copy-files:api": "copy-files-from-to --config copy-files-api.json",
		"postbuild:api": "yarn run copy-files:api",
		"e2e:ui": "yarn nx run ui-e2e:e2e",
		"affected": "yarn nx affected -t lint build e2e-ci",
		"prisma:generate": "./node_modules/.bin/prisma generate --schema=./apps/api/prisma/schema.prisma",
		"postinstall": "./node_modules/.bin/prisma generate --schema=./apps/api/prisma/schema.prisma",
		"skott": "./node_modules/.bin/skott --ignorePattern=\".yarn/**/*\" --ignorePattern=\"/**/jest.config.?s\" --ignorePattern=\"/**/jest.preset.?s\" --ignorePattern=\"/**/test-setup.?s\" --ignorePattern=\"/**/playwright.config.?s\" --ignorePattern=\"/**/webpack.config.?s\"",
		"skott:file-tree": "yarn run skott --displayMode=file-tree --showUnusedFiles",
		"skott:webapp": "yarn run skott",
		"firebase:deploy:functions": "firebase deploy --only functions",
		"prefirebase:deploy:functions": "yarn run copy-files:api",
		"pg:dump": "\"c:/Program Files/PostgreSQL/17/bin/pg_dump\" --clean --if-exists --quote-all-identifiers --host=localhost --port=5433 --username=benny --dbname=github --no-owner --no-privileges > c:/data/projects/nx/github/dump.sql",
		"pg:upload": "\"c:/Program Files/PostgreSQL/17/bin/psql\" --dbname=postgresql://postgres.cevlwdnlkvxcyiwpkhfk:githubnestangular123456@aws-0-eu-central-1.pooler.supabase.com:6543/postgres --file=dump.sql"
	},
	"private": true,
	"main": "dist/apps/api/main.js",
	"dependencies": {
		"@angular/animations": "^19.1.5",
		"@angular/cdk": "^19.1.3",
		"@angular/common": "^19.1.5",
		"@angular/compiler": "^19.1.5",
		"@angular/core": "^19.1.5",
		"@angular/forms": "^19.1.5",
		"@angular/platform-browser": "^19.1.5",
		"@angular/platform-browser-dynamic": "^19.1.5",
		"@angular/router": "^19.1.5",
		"@fortawesome/fontawesome-free": "^6.7.2",
		"@nestjs/axios": "^4.0.0",
		"@nestjs/common": "^11.0.9",
		"@nestjs/config": "^4.0.0",
		"@nestjs/core": "^11.0.9",
		"@nestjs/jwt": "^11.0.0",
		"@nestjs/passport": "^11.0.5",
		"@nestjs/platform-express": "^11.0.9",
		"@nestjs/swagger": "^11.0.3",
		"@ngrx/signals": "^19.0.1",
		"@prisma/client": "^6.3.1",
		"axios": "^1.7.9",
		"bcrypt": "^5.1.1",
		"bootstrap": "^5.3.3",
		"class-transformer": "^0.5.1",
		"class-validator": "^0.14.1",
		"cookie-parser": "^1.4.7",
		"firebase-admin": "^13.1.0",
		"firebase-functions": "^6.3.1",
		"lodash-es": "^4.17.21",
		"ngx-cookie-service": "^19.1.0",
		"passport": "^0.7.0",
		"passport-google-oauth20": "^2.0.0",
		"passport-jwt": "^4.0.1",
		"passport-local": "^1.0.0",
		"reflect-metadata": "^0.2.2",
		"rxjs": "^7.8.1",
		"skott": "^0.35.4",
		"tslib": "^2.8.1",
		"zone.js": "^0.15.0"
	},
	"devDependencies": {
		"@angular-devkit/build-angular": "^19.1.6",
		"@angular-devkit/core": "^19.1.6",
		"@angular-devkit/schematics": "^19.1.6",
		"@angular-eslint/eslint-plugin": "^19.1.0",
		"@angular-eslint/eslint-plugin-template": "^19.1.0",
		"@angular-eslint/template-parser": "^19.1.0",
		"@angular/build": "^19.1.6",
		"@angular/cli": "^19.1.6",
		"@angular/compiler-cli": "^19.1.5",
		"@angular/language-service": "^19.1.5",
		"@eslint/eslintrc": "^3.2.0",
		"@eslint/js": "^9.20.0",
		"@nestjs/schematics": "^11.0.0",
		"@nestjs/testing": "^11.0.9",
		"@nx/angular": "20.4.2",
		"@nx/devkit": "20.4.2",
		"@nx/esbuild": "20.4.2",
		"@nx/eslint": "20.4.2",
		"@nx/eslint-plugin": "20.4.2",
		"@nx/jest": "20.4.2",
		"@nx/js": "20.4.2",
		"@nx/nest": "20.4.2",
		"@nx/node": "20.4.2",
		"@nx/playwright": "20.4.2",
		"@nx/webpack": "20.4.2",
		"@nx/workspace": "20.4.2",
		"@playwright/test": "^1.50.1",
		"@pmmmwh/react-refresh-webpack-plugin": "^0.5.15",
		"@schematics/angular": "^19.1.6",
		"@svgr/webpack": "^8.1.0",
		"@swc-node/register": "^1.10.9",
		"@swc/core": "^1.10.15",
		"@types/bcrypt": "^5.0.2",
		"@types/bootstrap": "^5.2.10",
		"@types/cookie-parser": "1.4.8",
		"@types/express": "^5.0.0",
		"@types/jest": "^29.5.14",
		"@types/lodash-es": "^4.17.12",
		"@types/node": "^22.13.1",
		"@types/passport-google-oauth20": "^2.0.16",
		"@types/passport-jwt": "^4.0.1",
		"@types/passport-local": "^1.0.38",
		"@typescript-eslint/eslint-plugin": "^8.23.0",
		"@typescript-eslint/parser": "^8.23.0",
		"copy-files-from-to": "^3.12.0",
		"esbuild": "^0.25.0",
		"eslint": "^9.20.0",
		"eslint-config-prettier": "^10.0.1",
		"eslint-plugin-playwright": "^2.2.0",
		"globals": "^15.14.0",
		"jest": "^29.7.0",
		"jest-environment-jsdom": "^29.7.0",
		"jest-environment-node": "^29.7.0",
		"jest-preset-angular": "^14.5.1",
		"jsonc-eslint-parser": "^2.4.0",
		"nx": "20.4.2",
		"prettier": "^3.5.0",
		"prisma": "^6.3.1",
		"react-refresh": "^0.16.0",
		"ts-jest": "^29.2.5",
		"ts-node": "^10.9.2",
		"typescript": "5.7.3",
		"url-loader": "^4.1.1"
	}
}

[micalevisk]

you can run yarn why express to see non-dedup versions of express. You must ensure that you got only deduped versions of it. And this is not up to Nestjs-side to address (unless we got some bug)

[bhalperin]

@micalevisk all makes sense. Only thing is with 11.0.7 I had no issues, and the instances of express were the same. I stress my assumption that @nestjs/platform-express uses its own instance (v5).

[micalevisk]

I stress my assumption that @nestjs/platform-express uses its own instance (v5).

yes it does.

Try to drop the other versions; yarn why express to see from where they're coming

[bhalperin]

Found the root cause (though was not an issue in 11.0.7 or earlier):

The express instance in the root of my project was v4.21.2 and that's the one listed in npm and yarn package repos. So when running e.g. yarn add express, it installs v4.21.2. @nestjs/patform-browser however, installs v5.0.1. So I manually changed in package.json to "express": "^5.0.1" and after yarn install it compiled successully.

Now my app fails at runtime, but this may require other changes due to 11.0.8+.

Thanks all for your help and guidance.

[pavelkalin]

Maybe this info would be also helpful to someone else.
I have the same issue, I'm upgrading old express app to Nest gradually and having both express and Nest gives me this error.
When I had "@nestjs/platform-express": "11.0.7", all was good, with "@nestjs/platform-express": "11.0.9", this error appears:

reason: Error: 'app.router' is deprecated!
Please see the 3.x to 4.x migration guide for details on how to update your app

I've upgraded my old app to use current latest express version which is 4.21.2 and I don't use app.router anywhere in my project
In the error stack issue comes from
node_modules/@nestjs/platform-express/adapters/express-adapter.js:332:19)
which is

isMiddlewareApplied(name) {
const app = this.getInstance();
return (!!app._router &&
!!app.router.stack &&
(0, shared_utils_1.isFunction)(app.router.stack.filter) &&
app.router.stack.some((layer) => layer && layer.handle && layer.handle.name === name));
}

for transparancy this is what I have

npm ls express

myapp
├─┬ @nestjs/platform-express@11.0.9
.│....└── express@5.0.1
└── express@4.21.2

and I create my nest app via

export async function createNestApp(expressApp: express.Express) {
const nestApp = await NestFactory.create(NestModule, new ExpressAdapter(expressApp));
await nestApp.init();
}

where expressApp is my old app and const app = this.getInstance(); from PR gets it instead of express@5.0.1

I guess the right way is to upgrade to express version 5, as there app.router was back reintroduced
what @luddwichr explained here

I will stick with version 11.0.7 cause my app is big and I cannot upgrade to 5 now.
I will keep in mind that I might have issues with jsonParser along the way. Probably not as I'm passing express@4

[kamilmysliwiec]

I will stick with version 11.0.7 cause my app is big and I cannot upgrade to 5 now.

If you can't upgrade to express v5 yet, you should continue using Nest v10, not v11.