gistfile1.js

const fs = require('fs')
const axios = require('axios')

callback
fs.readFile('test.txt', 'utf-8', (err, str) => {
  if (err) {
    console.error('Something bad!' + err)
  }
 console.log(str)
})

const request = () => {
  return fs.promises.readFile('test.txt', 'utf-8').then((url) => {
    for (let i = 0; i < 10000; i++) {
      console.log(i)
    }
    return axios.get(url)
  })
}

request().then(response => {
  console.log(response.data)
})

console.log('Hey')


// // multi thread
// // 1 4 6 9 10
// // 2 3 5 7 8
// // ....

// // 1----3---2---

function login() {
  return new Promise((resolve, reject) => {
    setTimeout(() => { resolve() }, Math.random() * 1500)
  })
}

for (let i = 0; i < 3; i++) {
  login().then(() => { console.log('logged in ' + i)})
}

async function foo() {
  for (let i = 0; i < 3; i++) {
    await login().then(() => { console.log('logged in ' + i)})
  }
}

foo()
foo()

function* fibo() {
  let a = 1
  let b = 1
  while (true) {
    const sum = a + b
    a = b
    b = sum
    yield sum
  }
}

const gen = fibo()

console.log(gen.next().value)
console.log(gen.next().value)
console.log(gen.next().value)
console.log(gen.next().value)
console.log(gen.next().value)

const x = () => {
  this of parent
}

function x() {
  console.log(this)
}

const z = x.bind({}) // bound function
z()

var (without scope)
const | let

class A {
  foo() {
    console.log(this.x)
  }
}

class B extends A {
  constructor() {
    super()
    this.x = 1
  }

  foo() {
    console.log(this.x)
  }
}

const x = new B()

x.foo = function () {
  console.log(this.x)
}

x.foo = () => { console.log(this.x) }

x.foo()

1. x.foo ?
2. x.constructor.protype.foo ? (x.constructor = B)
3. x.constructor.constructor.prototype.foo

obj: prototype & constructor

function A() {
  // constructor
  this.x = 1
}

A.prototype.foo = function () {
  console.log(this.x)
}

const a = new A()
a.foo()

const { Server } = require('http')

const middleware = []

// app.use(bodyParser.JSON)
middleware.push((req, res, next) => {
  req.json = JSON.parse.data()
  next()
})


// a.js
const x = Symbol()
const an = {}
an[x] = '3'
an['x'] = 3
module.exports = an

// b.js
an.x = 4

const server = new Server(async (req, res) => {
  middleware[1](req, res, () => {
    middleware[2](req, res, () => {
      middleware[3]
    })
  })
})

server.listen(3000)

// -- native --
1233
false
undefined
typeof null is object!