ES6类执行多态性的能力 [英] ES6 Classes ability to perform polymorphism

问题描述

我正在尝试通过ES6类来模拟多态性，以便能够更好地理解该理论.

I am trying to emulate polymorphism through ES6 Classes, in order to be able to better understand this theory.

概念很明确(设计对象以共享行为，并能够用特定行为覆盖共享行为)，但我担心上面的代码不是有效的多态示例.

Concept is clear (designing objects to share behaviors and to be able to override shared behaviors with specific ones) but I am afraid my code above is not a valid polymorphism example.

由于我缺乏经验，如果您以全面的方式回答以下问题，我将不胜感激:

Due to my lack of experience, I appreciate if you answer these questions in a comprehensive way:

• 两个类都有一个同名的方法，并且每个类创建的实例都可以正确访问各自的方法，这使它成为一个多态示例吗?
• 如果这不效仿多态，应该进行哪些更改在代码中完成了吗?
• 我尝试删除 Employee.prototype = new Person(); 行，但该行仍然有效.这就是为什么我担心没有这个概念的原因.

• The fact that both Classes have an equally named method, and that instances made from each Class get access correctly to their respective methods, makes this a polymorphic example?
• In case this does not emulate polimorphism, what changes should be done in the code for it?
• I've tried removing the Employee.prototype = new Person(); line, and it still works. This is why I am afraid I'm not getting this concept.

class Person {
  constructor (name, age) {
    this._name = name;
    this._age = age;
  }
}

Person.prototype.showInfo = function(){
  return "Im " + this._name + ", aged " + this._age;
};


class Employee {
  constructor (name, age, sex) {
    this._name = name;
    this._age = age;
    this._sex = sex;
  }
}

Employee.prototype = new Person();

Employee.prototype.showInfo = function(){
  return "Im " + this._sex + ", named " + this._name + ", aged " + this._age;
};


var myPerson = new Person('Jon', 20);
var myEmployee = new Employee('Doe', 10, 'men');

document.write(myPerson.showInfo() + "<br><br>");   // Im Jon, aged 20
document.write(myEmployee.showInfo() + "<br><br>"); // Im men, named Doe, aged 10

推荐答案

每个JavaScript对象都有一个内部的原型"属性，通常称为[[prototype]]，该属性指向它直接继承的对象.

Every JavaScript object has an internal "prototype" property, often called [[prototype]], which points to the object from which it directly inherits.

每个JavaScript函数[object]都有一个属性原型，该原型由[几乎]空的对象初始化.当通过将其作为构造函数调用来创建此函数的新实例时，该新对象的[[prototype]]将指向构造函数的原型对象.

Every JavaScript function [object] has a property prototype, which is initialized with an [nearly] empty object. When you create a new instance of this function by calling it as a constructor, the [[prototype]] of that new object will point to the constructor's prototype object.

因此，当您编写此 var myPerson = new Person('Jon'，20); 时，您将拥有showInfo方法，因为您拥有

So, when you write this var myPerson = new Person('Jon', 20);,you have the method showInfo because you have this

Person.prototype.showInfo = function(){
    return "Im " + this._name + ", aged " + this._age;
};

使用ES6，如果您想了解多态性，可以这样做:

With ES6 if you want to see the polymorphism you could do that :

class Person {
    constructor (name, age) {
        this._name = name;
        this._age = age;
    }
        
    showInfo () {
        return "Im " + this._name + ", aged " + this._age;
    }
}

class Employee extends Person {
    constructor (name, age, sex) {
        super(name,age);
        this._sex = sex;
    }
        
    showInfo(){
        return "Im " + this._sex + ", named " + this._name + ", aged " + this._age;
    }
}

var myPerson = new Person('Jon', 20);
var myEmployee = new Employee('Doe', 10, 'men');

document.write(myPerson.showInfo() + "<br><br>");   // Im Jon, aged 20
document.write(myEmployee.showInfo() + "<br><br>"); // Im men, named Doe, aged 10

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