SyntaxError: negated character class with strings in regular expression

The JavaScript exception "negated character class with strings in regular expression" occurs when a v-mode character class is negated and may be able to match a string (more than one character).

Message

SyntaxError: Invalid regular expression: /[^\p{RGI_Emoji_Flag_Sequence}]/v: Negated character class may contain strings (V8-based)
SyntaxError: negated character class with strings in regular expression (Firefox)
SyntaxError: Invalid regular expression: negated class set may contain strings (Safari)

Error type

SyntaxError

What went wrong?

In v mode, character classes are able to match more than 1 character. For example, /[\q{abc}]/v would match the sequence "abc", and /[\p{RGI_Emoji_Flag_Sequence}]/v would match any character sequence that represents an emoji flag. However, negated character classes [^...] are not allowed to match strings, so /[^\p{RGI_Emoji_Flag_Sequence}]/v is invalid, because it's unclear how many characters it should match. For more information, see the v-mode character class reference.

Examples

Invalid cases

js
/[^\p{RGI_Emoji_Flag_Sequence}]/v;

Valid cases

js
// Matches two characters that are not an emoji flag sequence
/(?!\p{RGI_Emoji_Flag_Sequence})../v;

See also