Async handling for sync operations on server-side, leveraging EventLoop

async-operations-server.js

const express = require('express')

const sleep = (ms) => new Promise((res, rej) => setTimeout(res, ms))
const sleepSync = (ms) => {
  const start = new Date()
  while (new Date() - start < ms) {}
}

const server = express()

server.get('/heavy/:type', (req, res) => {
  console.log('heavy: start')

  const inner = () => {
      sleepSync(1000)
      res.send()
      console.log('heavy: done')
  }

  switch (req.params.type) {
    case 'raw':
      return inner()
    case 'setTimeout':
      return setTimeout(inner, 0)
    case 'setImmediate':
      return setImmediate(inner)
    case 'process.nextTick':
      return process.nextTick(inner)
    case 'Promise.resolve':
      return Promise.resolve().then(inner)
  }
})

server.get('/light/:id', (req, res) => {
  console.log(`light-${req.params.id}: start`)
  res.send()
  console.log(`light-${req.params.id}: done`)
})

server.listen(3000, () => console.log('server started'))

async-operations-test.js

const http = require('http')

const type = process.argv.slice(2).pop()

const main = async () => {
    http.get('http://localhost:3000/heavy/' + type)
    http.get('http://localhost:3000/light/1')
    http.get('http://localhost:3000/light/2')
}

main()