SyntaxError: incomplete quantifier in regular expression

The JavaScript exception "incomplete quantifier in regular expression" occurs when a regular expression pattern contains a {, but it does not start a valid quantifier.

Message

SyntaxError: Invalid regular expression: /1{/u: Incomplete quantifier (V8-based)
SyntaxError: incomplete quantifier in regular expression (Firefox)
SyntaxError: Invalid regular expression: incomplete {} quantifier for Unicode pattern (Safari)

Error type

SyntaxError

What went wrong?

A { character in a regular expression pattern starts a quantifier. A valid quantifier is in the form {n}, {n,}, or {n,m}, where n and m are non-negative integers and m is not less than n. If the { character does not start a valid quantifier, a SyntaxError occurs.

In Unicode-unaware mode, this syntax causes the { to become a literal character instead of generating an error, but this is a deprecated syntax and you should not rely on it.

Examples

Invalid cases

js
/1{/u;
/1{a}/u;
/1{}/u;
/1{1,2,3}/u;
/1{1, 2}/u;

Valid cases

js
/1{1}/u;
/1{1,}/u;
/1{1,2}/u;

See also