ES6：class的定义与继承，从ES5转换成ES6

1.ES5中class功能的实现：

var Person5 = function(name, yearOfBirth, job) {
  this.name = name; // 属性的添加
  this.yearOfBirth = yearOfBirth;
  this.job = job;
}

//添加方法：
Person5.prototype.calculateAge = function() {
  var age = new Date().getFullYear() - this.yearOfBirth;
  console.log(age);
}

var john5 = new Person5('John', 1999, 'teacher');

ES6中class的定义：

class Person6 {
  constructor(name, yearOfBirth, job) { //通过构造函数添加属性
    this.name = name;
    this.yearOfBirth = yearOfBirth;
    this.job = job;
  }
  calculateAge() { // 添加方法
    var age = new Date().getFullYear() - this.yearOfBirth;
    console.log(age);
  }

  static greeting() {
    console.log('Hey there!');
  }
}
const john6 = new Person6('John', 1999, 'teacher');

将john5 和 john6输出：

从上图可以看出john5和john6是一样的，所以es5和es6的效果是等价的。

2.继承

ES5实现继承：

var Athlete5 = function(name, yearOfBirth, job, olympicGames, medals) {
  Person5.call(this, name, yearOfBirth, job); // 通过call将this绑在Person5上
  this.olympicGames = olympicGames;
  this.medals = medals;
}

// 手动设置原型链
Athlete5.prototype = Object.create(Person5.prototype); // 先设置
Athlete5.prototype.wonMedal = function () { //再加自己的方法
    this.medals++;
    console.log(this.medals);
  }
var johnAthlete5 = new Athlete5('John', 1990,  'swimmer', 3, 10);
johnAthlete5.calculateAge();// 继承原型链上的方法
johnAthlete5.wonMedal();// 自己的方法

ES6实现继承：

class Athlete6 extends Person6 {
  constructor(name, yearOfBirth, job, olympicGames, medals) {
    super(name, yearOfBirth, job);
    this.olympicGames = olympicGames;
    this.medals = medals;
  }

  wonMedal() {
    this.medals++;
    console.log(this.medals);
  }
}

const johnAthlete6 = new Athlete6('John', 1990, 'swimmer', 3, 10);
johnAthlete6.calculateAge();
johnAthlete6.wonMedal();

输出johnAthlete5 和johnAthlete6，

说明johnAthlete5 和johnAthlete6是一样的，ES5和ES6等价。