SyntaxError: invalid regexp group

Message

SyntaxError: Invalid regular expression: /(?1)/: Invalid group (V8-based)
SyntaxError: invalid regexp group (Firefox)
SyntaxError: Invalid regular expression: unrecognized character after (? (Safari)

Error type

What went wrong?

? is not an atom, so it does not make sense to appear at the start of a capturing group (? is a quantifier and should be placed after an atom). Maybe you want to match the ? character literally, in which case you should escape it with a backslash (\?). Maybe you remembered the regex syntax wrong, and you intend to use one of the recognized group syntaxes listed above. Maybe you are using a feature that is not supported by the current JavaScript engine.

Examples

Invalid cases

/Hello(?|!)/;
// This is Perl syntax
/(?[\p{Thai}&\p{Digit}])/;

Valid cases

/Hello(\?|!)/;
// This is JavaScript syntax for character set operations
/[\p{Thai}&&\p{Digit}]/v;

See also

• Regular expressions
• Capturing group: (...)
• Lookahead assertion: (?=...), (?!...)
• Lookbehind assertion: (?<=...), (?<!...)
• Modifier: (?ims-ims:...)
• Named capturing group: (?<name>...)
• Non-capturing group: (?:...)