为什么这个正则表达式返回这样的数组

Question

我在MDN上遇到了这个关于字符串匹配方法的例子：

var str = "For more information, see Chapter 3.4.5.1";
var re = /(chapter \d+(\.\d)*)/i;
var found = str.match(re);

console.log(found);

// logs ["Chapter 3.4.5.1", "Chapter 3.4.5.1", ".1"]

// "Chapter 3.4.5.1" is the first match and the first value 
//  remembered from (Chapter \d+(\.\d)*).

// ".1" is the last value remembered from (\.\d)

我对JS上的RegExp上的匹配不是很清楚，似乎应该返回[＆＃34;第3.4.5.1节＆＃34;，＆＃34; .4.5.1＆＃34;]，任何人都可以解释一下结果是这样的。

Answer 1

    ["Chapter 3.4.5.1", "Chapter 3.4.5.1", ".1"]
      |                        |             |
      |                        |             |
Matched string           Characters inside Characters inside the group index 2. Basically `*` would do a greedy match. In this  (\.\d)* , it eats up all the `.\d` and captures only the last `.\d` part because you fail to capture the following `*` .
                          the group index
                              1    

DEMO

要获得所需的输出，您需要以此*模式捕获以下(\.\d)*，并且还需要删除第一个捕获组。

DEMO

> var str = "For more information, see Chapter 3.4.5.1";
undefined
> var re = /chapter \d+((?:\.\d)*)/i;
undefined
> str.match(re);
[ 'Chapter 3.4.5.1',
  '.4.5.1',
  index: 26,
  input: 'For more information, see Chapter 3.4.5.1' ]

Answer 2

str.match()会返回[whole regexp match, paren1match, paren2match ...]

的数组

要实现[“第3.4.5.1节”，“。4.5.1”]，您的代码应如下所示：

var str = "For more information, see Chapter 3.4.5.1";
var re = /chapter \d+([\.\d]*)/i;
var found = str.match(re);

console.log(found);