我可以“延伸”闭包定义的“类”在Javascript中？ [英] Can I "extend" a closure-defined "class" in Javascript?

问题描述

我有一个Javascript类定义如下：

I have a Javascript "class" defined like so:

var Welcomer = function(name) {
  var pName = name;
  var pMessage = function() {
    return "Hi, " + pName + "!";
  };

  return {
    sayHi: function() {
      alert(pMessage());
    }
  };
};

new Welcomer('Sue').sayHi();

有一个方法可以子类化 Welcomer 以这样的方式，我可以重新定义公共方法和访问私有方法和变量？下面将给我访问的公共方法，但不是私人的：

Is there a way to "subclass" Welcomer in such a way that I can redefine the public methods and have access to the private methods and variables? The following will give me access to the public methods, but not to the private ones:

var UnhappyWelcomer = function(name) {
  var pSadMessage = function() {
    // won't work, b/c I don't have access to pMessage
    return pMessage() + " Miserable day, innit?";
  };

  return {
    sayHi: function() {
      alert(pSadMessage());
    }
  };
};
UnhappyWelcomer.prototype = Welcomer(); // failed attempt at inheritance

new UnhappyWelcomer().sayHi();

推荐答案

您的问题的简单答案是否。

The simple answer to your question is No.

你不能做任何事情来访问那些 var 定义的东西，除非你的函数是一样的范围，或者你以某种方式公开信息（通过返回它或在 c>上设置）。

You can't do anything to gain access to those var defined things, unless your function is in the same scope, or you somehow 'make public' the information (by returning it, or setting it on this).

如果你有编辑原始函数的访问，你可以重写的方式，这些函数可以传递到一个扩展函数，这可以改变对象的protected范围。下面的代码应该能够很好地了解我的建议。

If you have access to edit the original function though, you could rewrite things in such a way that those functions could be "passed" into an extending function, which can alter the "protected" scope of the object. The following code should give a good idea of what I am proposing.

var Welcomer = function(name) {
  var _protected = {
    name: name,
    message: function() {
      return "Hi, " + _protected.name + "!";
    }
  };

  return {
    extendWith: function(extender) {
      extender.call(this, _protected);
      return this;
    },
    sayHi: function() {
      alert(_protected.message());
    }
  };
};

var UnhappyWelcomer = function(name) {
  var self = Welcomer(name).extendWith(function(_protected) {
    _protected.sadMessage = function() {
       return _protected.message() + " Miserable day, innit?";
    };
    // extending the public while still having scope to _protected...
    this.sayHi = function() {
      alert(_protected.sadMessage());
    };
  });
  return self;
};

UnhappyWelcomer('bob').sayHi();

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