JavaScript中的原型继承惯例 [英] Convention for prototype inheritance in JavaScript

问题描述

我看到很多这样的代码：

I see a lot of code like this:

function Base() {}
function Sub() {}
Sub.prototype = new Base();

但是，如果你这样做：

s = new Sub();
print(s.constructor == Sub);

这是假的。这对我来说似乎很困惑，因为s的构造函数确实是Sub。执行此操作是常规/更好吗？

This is false. This seems confusing to me, since s's constructor is, indeed, Sub. Is it conventional/better to do this?

function Base() {}
function Sub() {}
Sub.prototype = new Base();
Sub.prototype.constructor = Sub;

还是不重要？

推荐答案

'构造函数'不会像它看起来那样做。除了它的非标准之外，这是避免使用它的一个很好的理由 - 坚持使用instanceof和prototype。

'constructor' doesn't do what it looks like it does. This, in addition to its non-standardness, is a good reason to avoid using it - stick with instanceof and prototype.

技术上：'构造函数'不属于's'实例，它是'Sub'原型对象的一个​​属性。当您在Mozilla中创建Sub函数时，您将获得一个新创建的默认Sub.prototype对象，该对象具有指向Sub函数的构造函数作为礼貌。

Technically: 'constructor' is not a property of the 's' instance, it is a property of the 'Sub' prototype object showing through. When you create the 'Sub' function in Mozilla, you get a newly-minted default Sub.prototype object which has a 'constructor' pointing back to the Sub function as a courtesy.

但是，然后用新的Base（）替换该原型。返回Sub的原始默认原型丢失了;相反，Sub.prototype是Base的一个实例，没有任何重写的'constructor'属性。所以：

However you then replace that prototype with a new Base(). The original default prototype with the link back to Sub is lost; instead, Sub.prototype is an instance of Base without any overriding 'constructor' property. So:

new Sub().constructor===
Sub.prototype.constructor===
new Base().constructor===
Base.prototype.constructor===
Base

...一直到最基本的对象，你原型没有改变。

...all the way down to the most basic object whose prototype you didn't change.

是吗传统/更好地做到这一点？

Is it conventional/better to do this?

当处理JavaScript对象/类时，没有一个约定;每个库的元类系统的行为略有不同。我还没有看到一个手动为每个派生类编写'构造函数'的人，但是如果你真的想要真正的构造函数，它似乎是一个很好的解决方案;它还会使代码与不提供构造函数的浏览器/引擎兼容。

When dealing with JavaScript objects/classes there is no one convention; every library's metaclass system behaves slightly differently. I haven't seen one that writes 'constructor' to each derived class manually, but it seems as good a solution as any if you really want to have the real constructor available; it will also make the code compatible with browsers/engines that don't give you 'constructor'.

我会考虑给它一个不同的名称，以避免与现有的和不同行为的构造函数属性混淆。

I'd consider giving it a different name, though, to avoid confusion with the existing and differently-behaving 'constructor' property.

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