Curly braces in JavaScript regex is used to denote quantifiers. So writing a{2,4} will

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Asked: May 27, 20262026-05-27T19:18:24+00:00 2026-05-27T19:18:24+00:00

Curly braces in JavaScript regex is used to denote quantifiers. So writing

a{2,4}

will match aa, aaa and aaaa. But if you mistype this quantifier like this:

x{1,x}

It will match the literal text “x{1,x}”, at least in Firefox.

Is this behavior common to modern browsers?

The ECMA standard prohibits this behavior and requires the escaping of the braces.

(Background: I have to write a parser for javascript regexes at work.)

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Editorial Team · Answer 1 · 2026-05-27T19:18:25+00:00

Editorial Team

I don’t know for JavaScript and browsers, but this is the behaviour I would have expected and that I have seen in the past in regular expressions.

So I tested different regex engines on their behaviour:

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