Regexp backreferences

Dave Fugate dfugate at
Tue Aug 9 14:18:59 PDT 2011

Hi Paul, both of these tests were disabled on test262 about a month ago (see  In brief, chapter 16's extension clause regarding syntax errors implies these negative tests were invalid.  While I don't have the data available anymore,  we (Microsoft) did find some real world sites broke when the syntax error was thrown under these circumstances.  At the TC-39 meeting in May, we discussed making ES6 match the web in this regard - see  Hope this helps!


-----Original Message-----
From: es-discuss-bounces at [mailto:es-discuss-bounces at] On Behalf Of Paul Biggar
Sent: Tuesday, August 09, 2011 1:42 PM
To: test262-discuss at; es-discuss at
Subject: Regexp backreferences

[apologies for the duplicate post on test262@, my first attempt bounced on es-discuss@]

Hi folks,

Currently in SpiderMonkey, overlarge regex backreferences do not cause syntax errors. We are considering making them cause syntax errors for
test262 compliance, but are worried it will break the web.

As far as I can tell, we inherited our behaviour from Apple's Yarr, which took the behaviour from us, who originally copied IE back when that was important. Chrome does the same as us.

Does anyone have any idea or data as to whether this will break the web? If no such data exists, we can always just try it and see if it breaks things. Should this be removed form test262?


Firefox bug:

test262 test cases:

Paul Biggar
Compiler Geek
pbiggar at
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