NestJS as sub app of express.js vanilla

.babelrc

{
  "presets": [
    ["env", { "targets": {"node": "current" }, "debug": true }],
    "stage-0"
  ],
  
  "plugins": [
    "transform-decorators-legacy",
    "transform-runtime"
  ]
}

app.js

import express from 'express'
import bootstrapSubApp from './boot'

const app = express()

app.get('/', (req, res) => res.send('hello express'))

async function mountSubApp (app, mountPath, subAppBoot) {
  const subApp = await subAppBoot()
  await subApp.init()

  app.use(mountPath, subApp.getHttpAdapter().getInstance())
  return app
}

mountSubApp(app, '/onsub', bootstrapSubApp)
  .then(app => app.listen(4000))

boot.js

import { NestFactory } from '@nestjs/core'
import { SubAppModule } from './module'

async function bootstrap () {
  const app = await NestFactory.create(SubAppModule)

  return app
}

controller.js

import { Controller, Dependencies, Get } from '@nestjs/common'
import { SubAppService } from './service'

 @Controller('sub')
 @Dependencies(SubAppService)
 export class SubAppController {
   constructor (appService) {
     this.appService = appService
   }

   @Get()
   getHello () {
     return this.appService.getHello()
   }
 }

jsconfig.json

{
  "compilerOptions": {
    "target": "ES6",
    "experimentalDecorators": true
  },
  "exclude": [
    "node_modules"
  ]
}

module.js

import { Module } from '@nestjs/common'
import { SubAppController } from './controller'
import { SubAppService } from './service'

@Module({
  imports: [],
  controllers: [SubAppController],
  providers: [SubAppService]
})
export class SubAppModule {}

package.json

{
  "name": "express-with-nestjs-subapp",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "start": "babel-node src/app.js",
    "build": "babel src -d dist -s inline",
    "build:run": "npm run build && node dist/app.js"
  },
  "license": "ISC",
  "dependencies": {
    "@nestjs/common": "^5.5.0",
    "@nestjs/core": "^5.5.0",
    "express": "^4.16.4",
    "reflect-metadata": "^0.1.12",
    "rxjs": "^6.3.3"
  },
  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-core": "^6.26.3",
    "babel-plugin-external-helpers": "^6.22.0",
    "babel-plugin-transform-decorators-legacy": "^1.3.5",
    "babel-plugin-transform-runtime": "^6.23.0",
    "babel-polyfill": "^6.26.0",
    "babel-preset-env": "^1.7.0",
    "babel-preset-stage-0": "^6.24.1"
  }
}

service.js

import { Injectable } from '@nestjs/common'

@Injectable()
export class SubAppService {
  getHello () {
    return 'Hello from the Nest\n'
  }
}