SyntaxError: invalid character in class in regular expression

The JavaScript exception "invalid character in class in regular expression" occurs when a character appears in a v-mode character class but it's not allowed to appear literally.

Message

SyntaxError: Invalid regular expression: /[|]/v: Invalid character in character class (V8-based)
SyntaxError: invalid character in class in regular expression (Firefox)
SyntaxError: Invalid regular expression: invalid class set character (Safari)

Error type

SyntaxError

What went wrong?

Normally, character classes can contain almost all characters literally. However, the v mode made the character class syntax more sophisticated, and in order to leave room for future syntax extensions, some syntax characters are forbidden from appearing literally in a character class. They include: (, ), [, ], {, }, /, -, |. If you want to match these literal characters, escape them; for example: /[\|]/v.

Examples

Invalid cases

/[(){}]/v;

Valid cases

/[\(\)\\{\\}]/v;