http://xregexp.com/
What is it?
XRegExp is an open source (MIT license) JavaScript library that
provides an augmented, extensible, cross-browser implementation of
regular expressions, including support for additional syntax, flags,
and methods.
XRegExp is fully compliant with the regular expression flavor
specified in ECMA-262 Edition 3 (ES3), and has been tested with
Internet Explorer 5.5–8, Firefox 2–3.5, Safari 3–4, Chrome 1–3, and
Opera 9.5–10. It uses feature detection for its cross-browser support—
no browser sniffing.
Features
-Adds new regex and replacement text syntax, including comprehensive
support for named capture.
-Adds two new regex flags: s, to make dot match all characters (aka
singleline mode), and x, for free-spacing and comments (aka extended
mode).
-Provides a suite of 11 functions and methods that make complex regex
processing a breeze.
-Automagically fixes the most commonly encountered cross-browser
inconsistencies in regex behavior and syntax.
-Lets you easily create and use plugins that add new syntax and flags
to XRegExp's regular expression language.
User comments:
"For those of you so advanced in your RegEx powers that you've hit the
limitations of the built-in JavaScript implementation, check out
XRegExp, an open-source regular-expression library that supports named
capture and other advanced features."
"XRegExp [...] does some killer stuff that the native JS RegExp does
not; at only 2.4KB, it's a must-have for grepping and/or parsing on
the client side."
"XRegExp [...] adds some amazing features to stock JS capabilities."