计算Javascript中正则表达式的匹配数 [英] Count number of matches of a regex in Javascript

问题描述

我想写一个正则表达式来计算一大块文本中的空格/制表符/换行符的数量。所以我天真地写了以下内容： -

I wanted to write a regex to count the number of spaces/tabs/newline in a chunk of text. So I naively wrote the following:-

numSpaces : function(text) { 
    return text.match(/\s/).length; 
}

由于某些未知原因，它总是返回 1 。上述陈述有什么问题？我已经解决了以下问题： -

For some unknown reasons it always returns 1. What is the problem with the above statement? I have since solved the problem with the following:-

numSpaces : function(text) { 
    return (text.split(/\s/).length -1); 
}

推荐答案

tl; dr ：通用模式计数器

// THIS IS WHAT YOU NEED
const count = (str) => {
  const re = /YOUR_PATTERN_HERE/g
  return ((str || '').match(re) || []).length
}

对于那些到达这里的人来说，寻找一种通用的方法来计算字符串中正则表达式模式的出现次数，并且不想要如果出现零，则失败，此代码就是您所需要的。这是一个演示：

For those that arrived here looking for a generic way to count the number of occurrences of a regex pattern in a string, and don't want it to fail if there are zero occurrences, this code is what you need. Here's a demonstration:

/*
 *  Example
 */

const count = (str) => {
  const re = /[a-z]{3}/g
  return ((str || '').match(re) || []).length
}

const str1 = 'abc, def, ghi'
const str2 = 'ABC, DEF, GHI'

console.log(`'${str1}' has ${count(str1)} occurrences of pattern '/[a-z]{3}/g'`)
console.log(`'${str2}' has ${count(str2)} occurrences of pattern '/[a-z]{3}/g'`)

原始答案

初始代码的问题在于您错过了全局标识符：

The problem with your initial code is that you are missing the global identifier:

>>> 'hi there how are you'.match(/\s/g).length;
4

没有 g 正则表达式的一部分它只匹配第一个匹配项并停在那里。

Without the g part of the regex it will only match the first occurrence and stop there.

另请注意，正则表达式将连续计算两次空格：

Also note that your regex will count successive spaces twice:

>>> 'hi  there'.match(/\s/g).length;
2

如果不可取，​​你可以这样做：

If that is not desirable, you could do this:

>>> 'hi  there'.match(/\s+/g).length;
1

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