auto-updater for `npm start` if `package.json` file change

.gitignore

/package.lastInstall

package.json

{
  "scripts": {
    "prestart": "node ./preinstall"
  }
}

prestart.js

const fs = require('fs')

let lastInstall = null
let lastModified = null

// Retrieve lastInstall date. If `package.lastInstall` not exist or error during  rerieveing date, keep it `null`
try { lastInstall = fs.readFileSync('package.lastInstall', { encoding: 'utf8' }) } catch (error) {}
// Retrieve lastModified date on `package.json`. If `package.json` not exist or error during  rerieveing date, keep it `null`
try { lastModified = String(fs.statSync('package.json').mtime.getTime()) } catch (error) {}

// If any is null or date no match, execute an `npm i`
if (!lastInstall || !lastModified || lastModified !== lastInstall) {
  console.log('Updating ...')
  require('child_process').execSync('npm i', { stdio: 'inherit' })
  lastModified = String(fs.statSync('package.json').mtime.getTime())  // Retrieve the new `lastModified` date due to `npm i` alteration
  fs.writeFileSync('package.lastInstall', lastModified, { encoding: 'utf8' })
  console.log('Your system is up to date')
  
  // If an error happen during this process, script failed and exit. Add a try catch if you want another beaviour
} else {
  console.log('Your system is up to date')
}