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The JavaScript exception "duplicate capture group name in regular expression" occurs when a regular expression pattern contains two or more
with the same name, and these capture groups could be matched at the same time.
SyntaxError: Invalid regular expression: /(?<a>)(?<a>)/: Duplicate capture group name (V8-based) SyntaxError: duplicate capture group name in regular expression (Firefox) SyntaxError: Invalid regular expression: duplicate group specifier name (Safari)
All
in a regular expression pattern must have unique names. A more recent feature allows named capturing groups to share names, as long as they belong to different
and cannot be matched at the same time (see
for this). However, it is still an error if the named capturing groups with the same name could be matched at the same time, as that would make other features, such as
, ambiguous.
js
/(?<name>\w+) (?<name>\w+)/;
js
/(?<firstName>\w+) (?<lastName>\w+)/; /(?<year>\d{4})-\d{2}|\d{2}-(?<year>\d{4})/;
Named capturing group: (?<name>...)