javascript-class-multiple-inheritance

Introduction

ES6以后有了class关键字，可以方便地实现类的继承。但是JavaScript是一门单继承的语言，即一个类只能继承一个类。但是有时候我们需要多继承，这时候我们可以使用混入（mixin）来实现多继承。

Mixin

Mixin是一种实现多继承的方式，即将多个类的方法混入到一个类中。下面是一个简单的Mixin实现：

function mix(...mixins) {
  class Mix {}
  for (let mixin of mixins) {
    Object.assign(Mix.prototype, mixin);
  }
  return Mix;
}

// 定义两个mixin
const Flyable = {
  fly() { console.log("I can fly!"); }
};

const Swimmable = {
  swim() { console.log("I can swim!"); }
};

// 创建一个使用mixin的类
class Duck extends mix(Flyable, Swimmable) {}

let duck = new Duck();
duck.fly(); // 输出: I can fly!
duck.swim(); // 输出: I can swim!

Composition

class FlyBehavior {
  fly() { console.log("Flying with wings!"); }
}

class SwimBehavior {
  swim() { console.log("Swimming!"); }
}

class Duck {
  constructor() {
    this.flyBehavior = new FlyBehavior();
    this.swimBehavior = new SwimBehavior();
  }

  performFly() { this.flyBehavior.fly(); }
  performSwim() { this.swimBehavior.swim(); }
}

let duck = new Duck();
duck.performFly(); // 输出: Flying with wings!
duck.performSwim(); // 输出: Swimming!