如何在 Javascript 中使用多态性

Question

大多数语言对类使用单继承。这样做的模式相当明显（例如在下面的 Swift 代码中）。我仍在尝试围绕 JavaScript 中的模式来创建对象层次结构并重用类函数并覆盖类函数

class animal {
    func talk() {
        print ("?")
    }
}

class bird : animal {
    override func talk() {
        print("tweet tweet")
    }
    func fly() {
        print("flap flap")
    }
}

class parrot : bird {
    override func talk() {
        print("polly want a cracker")
    }
}

var a = animal()
var b = bird()
var p = parrot()

a.talk()  /// ?
b.talk()  /// tweet tweet
b.fly()   /// flap flap
p.talk()  /// polly want a cracker
p.fly()   /// flap flap

我认为我的问题是 Javascript 代码看起来不像这样。什么是等效的 Javascript 代码，以便我找出模式？

Answer 1

您几乎回答了自己的问题。你只需要学习 JavaScript 的语法。

我认为我的问题是 Javascript 代码看起来不像这样。

1. 如果一种语言看起来与另一种不同，这对您来说不是“问题”

2. 您提供的 Swift 代码在语法上非常接近您需要编写的 JavaScript (ES6) 以表达相同的类层次结构

class Animal {
  talk() {
    console.log('?')
  }
}

class Bird extends Animal {
  talk() {
    console.log('tweet tweet')
  }
  fly() {
    console.log('flap flap')
  }
}

class Parrot extends Bird {
  talk() {
    console.log('polly want a cracker')
  }
}

var a = new Animal()
var b = new Bird()
var p = new Parrot()

a.talk()
b.talk()
b.fly()
p.talk()
p.fly()

---

如果你想在 ES5 中设置一个“类”继承，你可以这样做

// Animal "class"
function Animal() {}

// Animal methods
Animal.prototype.talk = function talk() {
  console.log('?')
}

// ------------------------------
// Bird "class"
function Bird() {
  // if you want to call the parent constructor, you can do that here
  // Animal.call(this, arg1, arg2, ... argN)
}

// Bird inherits from Animal
Bird.prototype = Object.create(Animal.prototype)
Bird.prototype.constructor = Bird

// Bird methods
Bird.prototype.talk = function() {
  console.log('tweet tweet')
}
Bird.prototype.fly = function() {
  console.log('flap flap')
}

// ------------------------------
// Parrot "class"
function Parrot() {
  // if you want to call the parent constructor, you can do that here
  // Bird.call(this, arg1, arg2, ... argN)
}

// Parrot inherits from Bird
Parrot.prototype = Object.create(Bird.prototype)
Parrot.prototype.constructor = Parrot

// Parrot methods
Parrot.prototype.talk = function() {
  console.log('polly want a cracker')
}

var a = new Animal()
var b = new Bird()
var p = new Parrot()

a.talk()
b.talk()
b.fly()
p.talk()
p.fly()

Answer 2

有两个答案，ES6：

class animal {
    talk() {
        console.log("?")
    }
}

class bird extends animal {
    talk() {
        console.log("tweet tweet")
    }
    fly() {
        console.log("flap flap")
    }
}

class parrot extends bird {
    talk() {
        console.log("polly want a cracker")
    }
}

var a = new animal()
var b = new bird()
var p = new parrot()

a.talk()  /// ?
b.talk()  /// tweet tweet
b.fly()   /// flap flap
p.talk()  /// polly want a cracker
p.fly()   /// flap flap

和 ES5：

function animal() {

}

animal.prototype.talk = function () {
    console.log("?")
};

function bird() {
    animal.call(this)
}

bird.prototype = Object.create(
    animal.prototype,
    {constructor: {value: bird}}
);

bird.prototype.talk = function () {
    console.log("tweet tweet")
};

bird.prototype.fly = function () {
    console.log("flap flap")
};

function parrot() {
    bird.call(this);
}

parrot.prototype = Object.create(
    bird.prototype,
    {constructor: {value: parrot}}
);

parrot.prototype.talk = function () {
    console.log("polly want a cracker")
};


var a = new animal()
var b = new bird()
var p = new parrot()

a.talk()  /// ?
b.talk()  /// tweet tweet
b.fly()   /// flap flap
p.talk()  /// polly want a cracker
p.fly()   /// flap flap