构造函数

function M(x, y) {
  this.x = x
  this.y = y
}

M.prototype.add = function () {
  return this.x + this.y
}
let m = new M(5, 6)
console.log(m.add())

Class构造函数

class M {
  constructor(x, y) {
    this.x = x
    this.y = y
  }

  add () {
    return this.x + this.y
  }
}
const m = new M(5, 6)
console.log(m.add())

class的本质还是函数

class M {
  constructor(x, y) {
    this.x = x
    this.y = y
  }

  add () {
    return this.x + this.y
  }
}
const m = new M(5, 6)
console.log(typeof M) //funtion
console.log(M.prototype.constructor === M) //true
console.log(m.__proto__ === M.prototype) //true

Class 继承

class Animal {
  constructor(name) {
    this.name = name
  }
  eat () {
    console.log(this.name + 'eat')
  }
}
class Dog extends Animal {
  constructor (name) {
    super(name) // 必须写上
    this.name = name
  }
  say () {
    console.log(this.name + 'say')
  }
}
let dog = new Dog('哈士奇')
dog.say() //哈士奇say
dog.eat() //哈士奇eat

总结

• class更加贴近于面向对象的写法
• class 实现继承更加简单易懂，易理解
• 本质还是语法糖，使用prototype