我选择的答案不适合我……嗯……

只要在cow后面和/或milk前面添加空格，就可以从“always gives”中删除空格

/(?<=cow ).*(?= milk)/

Task

在两个字符串之间提取子字符串(不包括这两个字符串)

解决方案

let allText = "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum";
let textBefore = "five centuries,";
let textAfter = "electronic typesetting";
var regExp = new RegExp(`(?<=${textBefore}\\s)(.+?)(?=\\s+${textAfter})`, "g");
var results = regExp.exec(allText);
if (results && results.length > 1) {
    console.log(results[0]);
}

方法match()在字符串中搜索匹配项并返回Array对象。

// Original string
var str = "My cow always gives milk";

// Using index [0] would return<br/>
// "**cow always gives milk**"
str.match(/cow(.*)milk/)**[0]**


// Using index **[1]** would return
// "**always gives**"
str.match(/cow(.*)milk/)[1]

下面是一个正则表达式，它将抓取奶牛和牛奶之间的内容(没有前导/尾随空格):

srctext = "My cow always gives milk.";
var re = /(.*cow\s+)(.*)(\s+milk.*)/;
var newtext = srctext.replace(re, "$2");

示例:http://jsfiddle.net/entropo/tkP74/

我发现正则表达式是乏味和耗时的语法。因为你已经在使用javascript，所以不使用regex更容易做到以下几点:

const text = 'My cow always gives milk'
const start = `cow`;
const end = `milk`;
const middleText = text.split(start)[1].split(end)[0]
console.log(middleText) // prints "always gives"

您需要捕获。* 你可以(但不必)使。*非贪婪 真的没有必要向前看。 > /牛(. * ?)牛奶/我。exec(“我的奶牛总是产奶”); [“奶牛总是出奶”，“总是出奶”]