非捕获组：(?:...)

¥Syntax

(?:pattern)

¥Parameters

pattern

由你可以在正则表达式文字中使用的任何内容组成的模式，包括 disjunction。

¥Examples

¥Grouping a subpattern and applying a quantifier

在下面的示例中，我们测试文件路径是否以 styles.css 或 styles.[a hex hash].css 结尾。因为整个 \.[\da-f]+ 部分是可选的，为了对其应用 ? 量词，我们需要将其分组为一个新的原子。使用非捕获组不会创建我们不需要的额外匹配信息，从而提高性能。

¥In the following example, we test if a file path ends with styles.css or styles.[a hex hash].css. Because the entire \.[\da-f]+ part is optional, in order to apply the ? quantifier to it, we need to group it into a new atom. Using a non-capturing group improves performance by not creating the extra match information that we don't need.

function isStylesheet(path) {
  return /styles(?:\.[\da-f]+)?\.css$/.test(path);
}

isStylesheet("styles.css"); // true
isStylesheet("styles.1234.css"); // true
isStylesheet("styles.cafe.css"); // true
isStylesheet("styles.1234.min.css"); // false

¥Grouping a disjunction

析取在正则表达式中具有最低优先级。如果你想将析取用作更大模式的一部分，则必须将其分组。建议你使用非捕获组，除非你依赖析取的匹配文本。以下示例匹配文件扩展名，使用与 输入边界断言 文章相同的代码：

¥A disjunction has the lowest precedence in a regular expression. If you want to use a disjunction as a part of a bigger pattern, you must group it. You are advised to use a non-capturing group unless you rely on the matched text of the disjunction. The following example matches file extensions, using the same code as the input boundary assertion article:

function isImage(filename) {
  return /\.(?:png|jpe?g|webp|avif|gif)$/i.test(filename);
}

isImage("image.png"); // true
isImage("image.jpg"); // true
isImage("image.pdf"); // false

¥Avoiding refactoring hazards

捕获组可以通过它们在模式中的位置来访问。如果添加或删除捕获组，则还必须更新其他捕获组的位置（如果你通过匹配结果或 backreferences 访问它们）。这可能是错误的来源，特别是如果大多数组纯粹用于语法目的（应用量词或组析取）。使用非捕获组可以避免此问题，并且可以轻松跟踪实际捕获组的索引。

¥Capturing groups are accessed by their position in the pattern. If you add or remove a capturing group, you must also update the positions of the other capturing groups, if you are accessing them through match results or backreferences. This can be a source of bugs, especially if most groups are purely for syntactic purposes (to apply quantifiers or to group disjunctions). Using non-capturing groups avoids this problem, and allows the indices of actual capturing groups to be easily tracked.

例如，假设我们有一个与字符串中的 title='xxx' 模式匹配的函数（示例取自 捕获组）。为了确保引号匹配，我们使用反向引用来引用第一个引号。

¥For example, suppose we have a function that matches the title='xxx' pattern in a string (example taken from capturing group). To ensure the quotes match, we use a backreference to refer to the first quote.

function parseTitle(metastring) {
  return metastring.match(/title=(["'])(.*?)\1/)[2];
}

parseTitle('title="foo"'); // 'foo'

如果我们稍后决定添加 name='xxx' 作为 title= 的别名，我们将需要将析取分组到另一个组中：

¥If we later decided to add name='xxx' as an alias for title=, we will need to group the disjunction in another group:

function parseTitle(metastring) {
  // Oops — the backreference and index access are now off by one!
  return metastring.match(/(title|name)=(["'])(.*?)\1/)[2];
}

parseTitle('name="foo"'); // Cannot read properties of null (reading '2')
// Because \1 now refers to the "name" string, which isn't found at the end.

与其找到我们引用捕获组索引的所有位置并一一更新它们，不如避免使用捕获组：

¥Instead of locating all places where we are referring to the capturing groups' indices and updating them one-by-one, it's better to avoid using a capturing group:

function parseTitle(metastring) {
  // Do not capture the title|name disjunction
  // because we don't use its value
  return metastring.match(/(?:title|name)=(["'])(.*?)\1/)[2];
}

parseTitle('name="foo"'); // 'foo'

命名捕获组 是避免重构危险的另一种方法。它允许通过自定义名称访问捕获组，添加或删除其他捕获组时不受影响。

¥Named capturing groups are another way to avoid refactoring hazards. It allows capturing groups to accessed by a custom name, which is unaffected when other capturing groups are added or removed.

¥See also

• 组和反向引用 指南
• 正则表达式
• 捕获组：(...)
• 命名捕获组：(?<name>...)