在node.js中扩展类的不同方法 [英] Different ways of extending classes in node.js

问题描述

一般在node.js或javascript中扩展原型类。 （js newb）

Extending prototypical classes in node.js or javascript in general. (js newb)

我正在查看expressjs的源代码并看到这个：

I was looking at the source-code of expressjs and saw this:

var mixin = require('utils-merge'); 
....
mixin(app, proto);
mixin(app, EventEmitter.prototype);

Utils-merge 好像是一个外部模块。上面有什么区别，只是做了类似的事情：

Utils-merge seems like an external module. What are the difference of above and just doing something like:

var util = require('util');
....
util.inherit(app, proto);
util.inherit(app, EventEmitter);

这还在尝试扩展属性吗？我很善良 - 迷失在这里：

And is this still trying to extend properties? I'm kind-a lost here:

app.request = { __proto__: req, app: app }; // what is the equivalent for this in util?
app.response = { __proto__: res, app: app };

如果是这样，即使 util.inherit ？

app.request = util.inherit(app, req)

或类似的东西？ jshint说 __ proto __ 已被删除。

Or something like that? jshint says __proto__ is depricated.

另外我也看到了这个？

var res = module.exports = {
  __proto__: http.ServerResponse.prototype
};

这可能是吗？

var res = module.exports = util.inherits...??

推荐答案

我在看expressjs的源代码

I was looking at the source-code of expressjs

您可能还想查看这个问题关于如何 app 应该有效。

You might also want to have a look at this question about how app is supposed to work.

如上所述 utils-merge
之间有什么区别，只是做了类似的事情：

What are the differences between utils-merge as above and just doing something like:

var util = require('util');
....
util.inherit(app, proto);
util.inherit(app, EventEmitter);

他们做的事情完全不同：

They're doing totally different things:

utils-合并

将源对象中的属性合并到目标对象中。

util.inherits

util.inherits

将原型方法从一个构造函数继承到另一个构造函数。构造函数的原型将设置为从
superConstructor创建的新对象。

同时阅读他们的 来源！

app （由于奇怪的原因是一个函数）不是构造函数，但应该是一个（普通）对象 - 由<$ c $生成的实例 C> createApplication 。所以这里没有办法做类继承。并且你不能在同一个构造函数上多次使用 utils.inherits ，因为它覆盖 .prototype 它的属性。

app (while being a function for odd reasons) is not a constructor, but is supposed to be a (plain) object - an instance made by createApplication. So there's no way to do "class inheritance" here. And you cannot use utils.inherits multiple times on the same constructor anyways, as it does overwrite the .prototype property of it.

相反， mixin 函数只会复制<的所有属性code> proto 然后从 EventEmitter.prototype 到 app 的所有属性对象。

Instead, that mixin function will simply copy all the properties from proto and then all properties from EventEmitter.prototype to the app object.

这是否还在尝试扩展属性？我很善良 - 迷失在这里：

And is this still trying to extend properties? I'm kind-a lost here:

app.request = { __proto__: req, app: app }; // what is the equivalent for this in util?
app.response = { __proto__: res, app: app };

使用原生 Object.create 功能：

Use the native Object.create function for this:

app.request = Object.create(req);
app.request.app = app;
app.response = Object.create(res);
app.response.app = app;

如果是这样，即使 util.inherit ？

app.request = util.inherit(app, req) // Or something like that?

不，真的没有。

jshint说 __ proto __ 已被删除。

是的，您应该使用 Object.create 。但非标准 __ proto__ 可能会保留兼容性。

Yes, you should use Object.create instead. But the nonstandard __proto__ will probably be kept for compatibility.

此外我还看到了这个？

Additionally I also saw this?

var res = module.exports = {
  __proto__: http.ServerResponse.prototype
};

这可能是吗？

var res = module.exports = util.inherits...??

不，这是的情况Object.create ：

var res = module.exports = Object.create(http.ServerResponse.prototype);

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