请老师详细的说一下 以下代码 那些部分是生产代码 什么是生产代码的定义 和分辨方式

const express = require(‘express’)
const favicon = require(‘serve-favicon’)
const ReactSSR = require(‘react-dom/server’)
const path = require(‘path’)
const fs = require(‘fs’)
const prosess = require(‘prosess’)

const isDev = process.env.NODE_ENV === ‘development’
// const isDev = prosess.env.NODE_ENV === ‘development’

const app = express()

app.use(favicon(path.join(__dirname, ‘…/favicon.ico’)))

if (!isDev) {
const template = fs.readFileSync(path.join(__dirname, ‘…/dist/index.html’), ‘utf-8’)
const serverEntry = require(’…/dist/server-entry’).default
app.use(’/public’, express.static(path.join(__dirname, ‘…/dist’)))
app.get(’*’, function (req, res) {
const appString = ReactSSR.renderToString(serverEntry)
const app_template = template.replace(’’, appString) //eslint-disable-line
res.send(app_template)
})
} else {
const devStatic = require(’./util/dev-static’)
devStatic(app)
}

app.listen(3333, function () {
console.log(‘server is listening on 3333’)
})