yesvods

//mock a fs Object
let fs = {
  readFile: function(filename, cb){
    let randomTime = 100+Math.random()*1000>>0;
    
    setTimeout(()=>{
      cb(`hello ${filename}`)
    }, randomTime)
  }
}

yesvods

//ES6 Class inherit example
class Person{
  sayName(){
    console.log(this.name);
  }
}
class Classmate extends Person {
  constructor(name){
    super()
    this.name = name;

yesvods

let fs = {
  readFile: function(filename, cb){
    setTimeout(()=>{
      cb('hello')
    }, 100)
  }
}
let readFilePro = function(filename){
  return new Promise(function(resolve, reject) {
    fs.readFile(filename, (data, err) => {