As noted, JavaScript does not support lookbehind. However, there is a short collection of functions at https://gist.github.com/2387872 that make it easy to emulate positive and negative lookbehind in JavaScript. (Note that the linked code relies on the XRegExp library.)

It's a shame. I know ridgerunner from elsewhere on the Internet well enough to know that he is a regex expert and would've been a great asset here. I, too, mostly abandoned this forum years ago over frustration with it's UI and more. I'm amazed that some of the quality contributors like Aussie Susan and others still hang out here ...

Your analysis of the first and second passes is correct. However, this isn't really a browser issue--it follows the ECMAScript specification. And although it's true that the result is undefined because at the end you're left with a nonparticipating capturing group, the reason things end up that way is more specific. I've ...

If you're a JavaScript programmer and regular expression master (or want to be), check out the open source XRegExp library. Version 2 just hit the release candidate milestone yesterday, and brings a truckload of new features and improvements. Plus, if you want to match Unicode text in JavaScript, XRegExp is the only game in ...

I've just released XRegExp 1.0, the next generation of my JavaScript regular expression library. This version fixes a couple bugs, corrects even more cross-browser regex inconsistencies, and adds a suite of new regular expression functions and methods that make writing regex-intensive JavaScript applications easier than ever. One of these new ...

Regular Expressions Cookbook (written by Jan Goyvaerts and me, and published by O'Reilly Media) is now available at Amazon.com and other fine bookstores. The book covers eight programming languages equally (C#, Java, JavaScript, Perl, PHP, Python, Ruby, and VB.NET), but it's also useful for non-programmers. The majority of the content ...

This is really good stuff. Not only is it immediately the best online Java-flavor regex tester, but it's easily one of the best online regex testers, period. Nicely done.

Awesome tool, Lars (I've been using it for a while already). I like the simple interface and great set of regex flavor support. I'm definitely interested in seeing support for more flavors (as many as you can add!)

XRegExp is a JavaScript library that provides an augmented, cross-browser implementation of regular expressions, including support for additional modifiers and syntax. Several convenience methods and a new, powerful recursive-construct parser that uses regex delimiters are also included. Here's the feature list:Added regex syntax: ...

This is a fool's errand. Not to call Aussie Susan a fool (she certainly is not!), put perhaps unaware of the complexity of shielding against XSS attacks when allowing HTML input. This slideshow has some examples of the myriad ways one can maliciously run script, as well as some pointers about how to deal with HTML input safely: ...