首先定义一个父类

function Animal (name, age) {
  this.name = name
  this.age = age
  this.eat = function () {
    console.log('吃', this.name, this.age)
  }
}
Animal.prototype.drink = function () {
  console.log('喝', this.name, this.age)
}
// 实验一下
const test = new Animal('狗', 3)
test.eat()
test.drink()
console.log(test)

运行结果

1 使用extends实现继承

最简便的继承方式，仅支持ES6+

class Dog extends Animal {
  constructor(name, age, breed) {
    super(name, age)
    this.breed = breed
  }
  cry () {
    console.log('叫', this.name, this.age, this.breed)
  }
}
// 实验一下
  const dog = new Dog('狗', 3, '田园犬');
  dog.eat()
  dog.drink()
  dog.cry()
  console.log(dog)

实验结果

2 原型链继承

function Dog (name, age, breed) {
  Animal.call(this, name, age);
  this.breed = breed;
  this.cry = function () {
    console.log('叫', this.name, this.age, this.breed)
  }
}
Dog.prototype = new Animal()
Dog.prototype.constructor = Dog
// 实验一下
const dog = new Dog('狗', 3, '田园犬');
console.log(dog)
dog.eat()
dog.drink()
dog.cry()

实验结果

3 组合继承

function Dog (name, age, breed) {
  Animal.call(this, name, age);
  this.breed = breed;
  this.cry = function () {
    console.log('叫', this.name, this.age, this.breed)
  }
}
Dog.prototype = Object.create(Animal.prototype)
Dog.prototype.constructor = Dog
// 实验一下
const dog = new Dog('狗', 3, '田园犬');
console.log(dog)
dog.eat()
dog.drink()
dog.cry()

实验结果

4 寄生组合继承

function Dog (name, age, breed) {
  Animal.call(this, name, age);
  this.breed = breed;
  this.cry = function () {
    console.log('叫', this.name, this.age, this.breed)
  }
}
(() => {
  let Super = function () { };
  Super.prototype = Animal.prototype;
  Dog.prototype = new Super();
  Dog.prototype.constructor = Dog;
})();
// 实验一下
const dog = new Dog('狗', 3, '田园犬');
console.log(dog)
dog.eat()
dog.drink()
dog.cry()

实验结果

5 实例继承

function Dog (name, age, breed) {
  let dog = new Animal(name, age);
  dog.breed = breed;
  dog.cry = function () {
    console.log('叫', this.name, this.age, this.breed)
  }
  return dog
}
// 实验一下
const dog = new Dog('狗', 3, '田园犬');
console.log(dog)
dog.eat()
dog.drink()
dog.cry()

实验结果

6 拷贝继承

function Dog (name, age, breed) {
  let animal = new Animal(name, age);
  for (let key in animal) {
    this[key] = animal[key]
  }
  this.breed = breed;
  this.cry = function () {
    console.log('叫', this.name, this.age, this.breed)
  }
}
// 实验一下
const dog = new Dog('狗', 3, '田园犬');
console.log(dog)
dog.eat()
dog.drink()
dog.cry()

实验结果

7 扩展

7.1 函数中方法定义在函数内部、函数外、prototype上的区别

• 挂载在函数内部的方法，实例内部会复制构造函数的方法
• 挂载在原型上的方法，不会去复制。
• 挂载在内部和原型上的方法都是可以通过实例去调用的
• 一般来说，如果需要访问构造函数内部的私有变量，我们可以定义在函数内部，其他情况我们可以定义在函数的原型上
• 在函数外定义的方法，只能用类调用

7.2 class创建实例与构造函数创建实例

function exa1 (name, age) {
    this.name = name
    this.age = age
    this.innerFunc = function () {
      console.log('inner')
    }
  }
  exa1.prototype.outerFunc = function () {
    console.log('prototype')
  }
  exa1.getClassName = function () {
    console.log('example')
  }
  class exa2 {
    constructor(name, age) {
      this.name = name
      this.age = age
    }
    innerFunc = function () {
      console.log('inner')
    }
    outerFunc () {
      console.log('prototype')
    }
    static getClassName () {
      console.log('example')
    }
  }
  console.log(new exa1(), new exa2())