如何在JavaScript正则表达式中访问匹配的组？

问题：

I want to match a portion of a string using a regular expression and then access that parenthesized substring: 我想使用正则表达式匹配字符串的一部分，然后访问带括号的子字符串：

var myString = "something format_abc"; // I want "abc"

var arr = /(?:^|\s)format_(.*?)(?:\s|$)/.exec(myString);

console.log(arr);     // Prints: [" format_abc", "abc"] .. so far so good.
console.log(arr[1]);  // Prints: undefined  (???)
console.log(arr[0]);  // Prints: format_undefined (!!!)

What am I doing wrong? 我究竟做错了什么？

I've discovered that there was nothing wrong with the regular expression code above: the actual string which I was testing against was this: 我发现上面的正则表达式代码没有任何问题：我要针对的实际字符串是：

"date format_%A"

Reporting that "%A" is undefined seems a very strange behaviour, but it is not directly related to this question, so I've opened a new one, Why is a matched substring returning "undefined" in JavaScript? 报告“％A”未定义似乎是一种非常奇怪的行为，但它与该问题没有直接关系，因此我打开了一个新的代码， 为什么匹配的子字符串在JavaScript中返回“未定义”？ . 。

The issue was that console.log takes its parameters like a printf statement, and since the string I was logging ( "%A" ) had a special value, it was trying to find the value of the next parameter. 问题是console.log像printf语句一样接受其参数，并且由于我正在记录的字符串（ "%A" ）具有特殊值，因此它试图查找下一个参数的值。

解决方案：

参考一： https://stackoom.com/question/1oVh/如何在JavaScript正则表达式中访问匹配的组
参考二： https://oldbug.net/q/1oVh/How-do-you-access-the-matched-groups-in-a-JavaScript-regular-expression

来源：oschina

链接：https://my.oschina.net/u/4428122/blog/4486081

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javascript