克罗克福德的深化方法 - “好部件”第41页 [英] Crockford's deentityify method - p.41 of The Good Parts

问题描述

在一系列自我改进中，我正在阅读（并重读）SeñorCrockford的TGP。然而，我不能理解他的深化方法的中间部分。

  ... 
 return this.replace（ ...，
函数（a，b）{
 var r = ... 
} 
）; 
  

我想我明白了：

1. this.replace传递了两个参数，正则表达式作为搜索值和函数来生成重置值;
   
2. b用于访问属性实体对象;
   
3. 返回？ r：a; 位确定是返回文本还是实体中相应属性的值。
   

我根本得不到的是a& b作为参数提供给函数（a，b）。什么叫这个功能？ （我知道整个事情是自动执行的，但是这并不能真正为我清除它，我猜我在问这个函数是如何被调用的？）

如果有人有兴趣通过类似于这个，我真的很感激它，我怀疑其他人也可能。

以下是方便的代码：

  String.method（'deentityify'，function（）{
 var entity = {
 quot;'''，
 lt;'，
 gt：'>'
}; 
 
 return function（）{
 return this.replace（
 / &（[^& ;;] +）; / g，
函数（a，b）{
 var r = entity [b]; 
返回typeof r ==='string '？r：a; 
} 
）; 
}; 
}（））; 
  

解决方案

a 不是数字偏移量，它是匹配子字符串。 $ b b （在这种情况下）是第一个分组，即匹配减去周围的& 和; 。

该方法检查以确保实体存在，并且它是一个字符串。如果是，那就是重置价值，否则它会被原来的价值减去& 和;

In a fit of self-improvement, I'm reading (and rereading) TGP by Señor Crockford. I cannot, however, understand the middlemost part of his deentityify method.

...
return this.replace(...,
    function (a, b) {
       var r = ...
    }
);

I think I understand that:

1. this.replace is passed two arguments, the regex as the search value and the function to generate the replacement value;
2. the b is used to access the properties in the entity object;
3. the return ? r : a; bit determines whether to return the text as is or the value of the appropriate property in entity.

What I don't get at all is how the a & b are provided as arguments into function (a, b). What is calling this function? (I know the whole thing is self-executing, but that doesn't really clear it up for me. I guess I'm asking how is this function being called?)

If someone was interested in giving a blow by blow analysis akin to this, I'd really appreciate it, and I suspect others might too.

Here's the code for convenience:

String.method('deentityify', function ( ) {
    var entity = {
        quot: '"',
        lt: '<',
        gt: '>'
    };

    return function () {
        return this.replace(
            /&([^&;]+);/g,
            function (a, b) {
                var r = entity[b];
                return typeof r === 'string' ? r : a;
            }
        );
    };
}()); 

解决方案

a isn't the numerical offset, it's the matched substring.

b (in this case) is the first grouping, i.e., the match minus the surrounding & and ;.

The method checks to make sure the entity exists, and that it's a string. If it is, that's the replacement value, otherwise it's replaced by the original value, minus the & and ;

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