server.js

const cacheableResponse = require('cacheable-response')
const express = require('express')
const next = require('next')
const config = require('config')
const { Mutex } = require('async-mutex')
const cookieParser = require('cookie-parser')

const port = parseInt(process.env.PORT, 10)
const app = next({ dev: false }) // only for prod mode
const handle = app.getRequestHandler()
const mutexMap = {}

const getSrrCache = (ttl) => cacheableResponse({
  ttl,
  get: async ({ req, res }) => {

    const data = await app.renderToHTML(req, res, req.path, {
      ...req.query,
      ...req.params
    })
    if (res.statusCode === 404) {
      res.end(data)
      return {}
    }
    return { data }
  },
  send: ({ data, res }) => res.send(data)
})

const noStaticCache = getSrrCache(config.TTL_NO_STATIC)

const lockWrapper = async (req, res, typeCash) => {
  if (!mutexMap[req.originalUrl]) {
    mutexMap[req.originalUrl] = new Mutex()
  }
  const release = await mutexMap[req.originalUrl].acquire()
  try {
    await typeCash({ req, res })
  } finally {
    release()
  }
}

app.prepare().then(() => {
  const server = express()

  server.use(cookieParser())

  server.get('/', (req, res) => lockWrapper(req, res, noStaticCache))
  server.get('*', (req, res) => handle(req, res))

  server.listen(port, (err) => {
    if (err) throw err
    // eslint-disable-next-line no-console
    console.log(`> Ready on: ${port}`)
  })
})