sequential, parallel and pooled Promise resolving

promise-resolving.ts

import * as request from 'request'
import * as $ from 'cheerio'
let PromisePool = require("es6-promise-pool") //no typings definition

var sites = [
  'http://www.microsoft.com',
  'http://www.apple.com',
  'http://stackoverflow.com',
  'https://github.com'
]

var getBody = (site: string): Promise<string> => {
  return new Promise((resolve, reject) => {
    console.log(`Requesting: ${site}...`)
    request.get(site, (error, response, body) => {
      console.log(`Done: ${site}...`)
      if (error)
        reject(error)
      resolve(body)
    })
  })
}

var sequential = (async () => {
  for (let site of sites) {
    var body = await getBody(site)
    console.log(site, $("title", body).text())
  }
})

var parallel = (async () => {
  var result = await Promise.all(sites.map(getBody))

  for (let i = 0; i < result.length; i++) {
    console.log(sites[i], $("title", result[i]).text())
  }
})

var pooled = (async () => {
  let i = -1
  let pool = new PromisePool(() => {
    if (sites.length > ++i) {
      return Promise.all([sites[i], getBody(sites[i])])
    }
    return null
  }, 5)

  pool.addEventListener('fulfilled', function(event) {
    console.log(event.data.result[0], $("title", event.data.result[1]).text())
  })

  pool.addEventListener('rejected', function(event) {
    console.log('Rejected', event.data.error)
  })

  await pool.start()
})

let timer = function(name) {
  let start = new Date();
  return {
    stop: function() {
      var end = new Date();
      var time = end.getTime() - start.getTime();
      return time;
    }
  }
};

var go = (async () => {
  let result: any = {}

  let seq = timer('Sequential')
  await sequential()
  result.sequential = seq.stop();

  let par = timer('Parallel')
  await parallel()
  result.parallel = par.stop();

  let pol = timer('Pooled')
  await pooled()
  result.pooled = pol.stop();

  console.log(result)
})()