Javascript正则表达式中被动（非捕获）组的目的是什么？ [英] What is the purpose of the passive (non-capturing) group in a Javascript regex?

问题描述

Javascript正则表达式中被动组的目的是什么？

What is the purpose of the passive group in a Javascript regex?

被动组的前面是一个问号冒号：（？ ：group）

The passive group is prefaced by a question mark colon: (?:group)

换句话说，这两件事情看起来是一样的：

In other words, these 2 things appear identical:

"hello world".match(/hello (?:world)/)
"hello world".match(/hello world/)

在什么情况下你需要非捕获组以及为什么？

In what situations do you need the non capturing group and why?

推荐答案

非捕获与普通（捕获）组只有一个区别：它们不需要正则表达式引擎记住它们匹配的内容。

Non-capturing have just one difference from "normal" (capturing) groups: they don't require the regex engine to remember what they matched.

用例是有时你必须（或应该）使用一个组，不是因为你对它所捕获的内容感兴趣而是出于语法原因。在这些情况下，使用非捕获组而不是标准捕获组是有意义的，因为它不太占用资源 - 但如果您不关心它，捕获组将以完全相同的方式运行。

The use case is that sometimes you must (or should) use a group not because you are interested in what it captures but for syntactic reasons. In these situations it makes sense to use a non-capturing group instead of a "standard" capturing one because it is less resource intensive -- but if you don't care about that, a capturing group will behave in the exact same manner.

您的具体示例并不能很好地使用非捕获组，因为这两个表达式完全相同。一个更好的例子可能是：

Your specific example does not make a good case for using non-capturing groups exactly because the two expressions are identical. A better example might be:

input.match(/hello (?:world|there)/)

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