SyntaxError: Invalid regular expression: /\b+/: Nothing to repeat (V8-based)SyntaxError: Invalid regular expression: /(?=)+/u: Invalid quantifier (V8-based)SyntaxError: nothing to repeat (Firefox)SyntaxError: invalid quantifier in regular expression (Firefox)SyntaxError: Invalid regular expression: nothing to repeat (Safari)

Quantifiers are used to specify how many times a character or group of characters can appear in a regular expression. For example,a{3} matches the charactera exactly three times. Therefore, if the thing preceding the quantifier is not something that matches characters, the quantifier is invalid. For example: quantifiers at the start of acapturing group, at the start of adisjunction alternative, etc., cannot repeat anything.Assertions don't consume characters, so it also doesn't make sense to repeat them.

InUnicode-unaware mode, there's a deprecated syntax that allows thelookahead assertions to be quantified. This is a deprecated syntax and you should not rely on it.

• Regular expressions
• Quantifier:*,+,?,{n},{n,},{n,m}