JavaScript封装 [英] JavaScript Encapsulation

问题描述

所以我一直在研究完全开发面向对象的JavaScript实践，并对以下示例感到疑惑。

So I've been looking into full development object oriented JavaScript practices, and wonder about the following examples.

据我了解，（并且它有意义me）以下'秘密'字段是'私人'：

As I understand it, (and it makes sense to me) that the following 'secret' field is 'private' :

var MyObject = function() {

    var secret = 'sshhh';

    this.getSecret() = function() {
        return secret;
    }

}

这是因为现场保密具有内部功能可以访问的功能范围，但没有任何外部...到目前为止一切都很好。

and this is because the field secret has function scope that the inner function can access, but nothing outside ... so far so good.

但是我已经看到了以下内容（特别是道格拉斯克罗克福德的书）：

But I've seen the following around (and especially in Douglas Crockford's book) :

var MyObject = function() {

    var secret = 'sshhh';

    return {
       getSecret : function() {
            return secret;
       }
    }   

}();

并且想知道区别是什么，为什么它更好？据我所知，在这种情况下，我们甚至没有返回私有字段所在的同一个对象，但由于无法直接访问该字段，因此看不到很大的好处。

and was wondering what the difference is, why is it better? I understand that in this case we're not even returning the same object that the private field exists in, but don't see a huge benefit as you can't access the field directly either way.

推荐答案

这些例子非常不同......第一个创建一个MyObject函数，当被调用时作为使用 new 的构造函数，将具有getSecret函数作为属性;第二个创建一个MyObject Object ，并将getSecret函数作为属性。

Those examples are very different... The first creates a "MyObject" function that, when called as a constructor using new, will have a "getSecret" function as a property; the second creates a "MyObject" Object with a "getSecret" function as a property.

在这方面，这有点像静态方法和公共方法之间的区别。在第一种情况下，该方法仅在调用构造函数时存在，而不是在构造函数本身中存在。在第二种情况下，没有构造函数。

In that respect, this is sort of like the difference between a static method and a public method. In the first case, the method only exists when the constructor is called, not in the constructor itself. In the second case there is no constructor.

所以假设你有：

var MyObject1 = function() {
  var secret = 'sshhh';
  this.getSecret = function() {
    return secret;
  }
}

// ...

var MyObject2 = function() {
  var secret = 'sshhh';
  return {
    getSecret : function() {
      return secret;
    }
  }
}();

运行一些测试：

MyObject1.getSecret();
// TypeError: Object has no method 'getSecret'
var m1 = new MyObject1();
m1.getSecret();
// "sshhh"

MyObject2.getSecret();
// "sshhh"
var m2 = new MyObject2();
// TypeError: object is not a function

所以MyObject1就像一个类， MyObject2就像一个静态类。

So MyObject1 is like a class, and MyObject2 is like a static class.

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