对JavaScript原型继承感到困惑

问题描述

在 JavaScript权威指南5版一书中，9.2节原型和继承，我找到以下字样：

现在，如果确实如此，原型继承如何存在？我的意思是，假设构造函数的原型对象最初具有构造函数属性。因为原型对象本身是一个对象，为了确定它的构造函数，我们经常使用 prototype_object.constructor 。但是现在 prototype_object 已经有一个构造函数属性本身，它指向 构造函数与原型相关联的 。在这种情况下，如何存在继承？

解决方案

让我们说，狗是一个哺乳动物。

  function Mammal（）{
 this.milk = true; 
}; 
 
 
 
 function Dog（）{
 this.bark = true; 
} 
 Dog.prototype =新的哺乳动物; 

所以Dog points的原型到哺乳动物的对象。这个Mammal对象有一个对它的构造函数的引用，所以当Dog是新的时，JavaScript看到Dog原型是一个哺乳动物，所以调用Mammal的构造函数来生成一个有效的Mammal对象（另一个）然后使用Dog构造函数使它成为Dog对象。 p>

从这里， Dog.prototype 的构造函数是 Mammal （添加了额外字段和函数的哺乳动物对象） Dog 的构造函数是 Dog 。遗传的存在是因为Dog的一个实例以哺乳动物为原型;因此，狗是一个哺乳动物。当一个方法被调用并且JS无法从 Dog.prototype 中找到它时，JS会查看 Mammal.prototype （这是添加了额外字段和函数的Object。）

希望这会有所帮助。

In the book "JavaScript the definitive guide 5 edition", section 9.2 Prototypes and Inheritance, I find the following words:

Now, if that is true, how could prototypal inheritance exists? I mean, let's say the prototype object of a constructor function has a constructor property initially. Because the prototype object itself is an object, to determine its constructor we often use prototype_object.constructor. But now the prototype_object already has a constructor property itself, and it points to the constructor function with which the prototype is associated. In this situation how can inheritance exists?

解决方案

Let say, Dog is a Mammal.

function Mammal() {
  this.milk = true;
};


function Dog() {
  this.bark = true;
}
Dog.prototype = new Mammal;

So prototype of Dog points to an object of Mammal. This Mammal object has a reference to its constructor so when Dog is new, JavaScript see that Dog prototype is a Mammal so Mammal's constructor is called to produce a valid Mammal object (another one) then make it a Dog object using Dog constructor.

From this, the constructor of Dog.prototype is a Mammal (a Mammal Object that has extra fields and functions added) BUT constructor of Dog is Dog. The inheritance exist because the an instance of Dog has a Mammal as a prototype; hence, Dog is a Mammal. When a method is called and JS cannot find it from Dog.prototype, JS look in Mammal.prototype (which is an Object that has extra fields and functions added).

Hope this helps.

这篇关于对JavaScript原型继承感到困惑的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！