npm startで複数のNode.jsのアプリケーションを立ち上げたい

"scripts": {
    "start": "concurrently \"npm -prefix ./1つ目のアプリのディレクトリ/ start\" \"npm -prefix ./2つ目のアプリのディレクトリ/ start\""
}

let fs = require('fs')

let admin = require('firebase-admin')
let serviceAccount = require('秘密鍵')

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  databaseURL: "https://プロジェクトID.firebaseio.com"
})

setInterval(viroBackup, 5000)

function viroBackup () {
  let db = admin.database()
  db.ref('/').once('value', (snapshot) => {
    let now = new Date()
    let dirName = now.getFullYear() + '-' + (Number(now.getMonth()) + 1) + '-' + now.getDate()
    let fileName = now.getHours() + '_' + now.getMinutes() + '_' + now.getSeconds() + '_bk.json';
    if (!fs.existsSync(dirName)) {
      fs.mkdirSync(dirName)
    }
    fs.writeFileSync('./' + dirName + '/' + fileName, JSON.stringify(snapshot.val(), null, 4))
  })
}