原型混淆:父原型属性受子原型影响 [英] prototype confusion: parent prototype property affected by child prototype

问题描述

我正在阅读一本关于 OOP javascript 的书，但被其中的一个例子困住了.

I'm reading a book on OOP javascript and got stuck on one of the examples.

在示例代码的第一个版本中，创建了 Shape 构造函数的新实例并调用了 toString 方法.toString 方法返回Triangle"，它是 Triangle 原型的 name 属性，即使Shape"应该是 Shape 原型的 >name 属性.

In the first version of the sample code, a new instance of the Shape constructor function is created and the toString method is called. The toString method returns "Triangle" which is the name property of the Triangle prototype, even though "Shape" is supposed to be the name property of the Shape prototype.

在示例代码的第二个版本中，toString 方法按预期返回Shape".我想知道代码的第二个版本中的更改如何产生任何不同，因为在示例代码的两个版本中，Triangle 原型都包含对 Shape 原型所以 Shape 原型的 name 属性仍然会更新为Triangle"，因为 Triangle.prototype.name = "Triangle";

In the second version of the sample code, the toString method returns "Shape" as intended. I'm wondering how the changes in the second version of the code made any difference because it seems like in both versions of the sample code, the Triangle prototype holds a reference to the Shape prototype so the name property of the Shape prototype would still be updated to "Triangle" because of Triangle.prototype.name = "Triangle";

第一个版本:jsfiddle

第二个版本:jsfiddle

推荐答案

在第二个例子中，当你分配了 Triangle.prototype = new F(); 那么一个新的 F 实例函数 已经创建并且它继承了 Shape 的原型，这意味着 Triangle.prototype 中的任何变化都将反映在该对象实例中，而不是在 F 的构造函数，因为一个对象实例不能改变它的构造函数，但是如果你在 constructor'sprototype/Shape.prototype 中改变，那么由该构造函数创建的任何对象也将被反映.但是如果你被分配了 Triangle.prototype = F.prototype 它可能会有所不同.

In the second example,when you assigned Triangle.prototype = new F(); then a new instance of F function has been created and it inherited prototype of Shape which means any changes in Triangle.prototype will be reflected in that object instance but not in the F's constructor, because an object instance can't change it's constructor but if you change in the constructor's prototype/Shape.prototype then any object that created by that constructor function will be reflected too. But if you were assigned Triangle.prototype = F.prototype it could be different.

我在此处做了一些更改.希望能帮助你理解，在控制台查看.

I've made some changes here. Hope it'll help you to understand, see in the console.

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