Async, Await / Promise

var request = require('request');

/* version 1: Normal,
function google(next = () => { }) {

  request('https://www.google.com').on('response', function (err, body) {
    console.warn('google arrive');
    next();
  })
}

function yahoo(next = () => { }) {
  request.get('https://www.yahoo.com').on('response', function (err, body) {
    console.warn('yahoo arrive');
    next();
  })
}

/*
Version 2: Promise,
function google(next=()=>{}) {
  return new Promise(function(resolve, reject){
    request('https://www.google.com').on('response', function (err, body) {
      console.warn('google arrive');
      next();
      resolve();
    })
  });
}

function yahoo(next=()=>{}) {
  return new Promise(function(resolve, reject){
    request.get('https://www.yahoo.com').on('response', function (err, body) {
      console.warn('yahoo arrive');
      next();
      resolve();
    })
  });
}*/


/*google(()=>{
  yahoo(()=>{
    google();
  })
})*/


/*google()
.then(()=>{
  return yahoo();
}).then(()=>{
  return google();
})*/


function google(next = () => { }) {
  return new Promise(function (resolve, reject) {
    request('https://www.google.com').on('response', function (err, body) {
      console.warn('google arrive');
      next();
      resolve();
    })
  });
}

function yahoo(next = () => { }) {
  return new Promise(function (resolve, reject) {
    request.get('https://www.yahoo.com').on('response', function (err, body) {
      console.warn('yahoo arrive');
      next();
      resolve();
    })
  });
}

async function seq(){
  await google();
  await yahoo();
  await google();
}

seq();

由於尚未支援到async/await ES7 的 feature 所以必須設定flag 打開此feature

node --harmony-async-await index.js