Month: July 2010

Do you regularly post regular expressions online? Have you seen the regex syntax highlighting in RegexPal, RegexBuddy, or on my blog (example), and wanted to apply it to your own websites? Prompted by blog reader Mark McDonnell, I've extracted the regex syntax highlighting engine built into RegexPal and made it into its own library, unimaginatively named JavaScript Regex Syntax Highlighter. When combined with the provided CSS, this 1.6 KB self-contained JavaScript file can be used, for instance, to automatically apply regex syntax highlighting to any HTML element with the "regex" class. You can see an example of doing just that on my quick and dirty test page. Although the library is simple (there's just one function to call), the syntax highlighting is pretty advanced and handles all valid JavaScript regex syntax and errors (with errors highlighted in red). An example of its advanced highlighting support is that it knows, based on the context, whether \10 is backreference 10, backreference 1 followed by a literal zero, octal character index 10, or something else altogether due to its position in the surrounding pattern. Speaking of octal escapes (which are de facto browser extensions; not part of the spec.), they are correctly highlighted according to their subtle differences inside and outside character classes (outside of character classes only, octals can include a fourth digit if the leading digit is a zero). As far as I'm aware, this is the first JavaScript library for highlighting regex syntax, with or without the level of completeness included here. For people who might feel inclined to use or improve upon my work, I've made the licensing as permissive as possible to avoid getting in your way. RegexPal is already open source under the GNU LGPL 3.0 License, but this new library is released under the MIT License. If you plan to customize or help upgrade this code, note that it could probably use a bit of an overhaul (it's ripped from RegexPal with minimal modification), and might require an overhaul if you want to cleanly add support for additional regex flavors. Another nifty feature I plan to eventually add is explanatory title attributes for each element in the returned HTML, which might be particularly helpful for deciphering any highlighted errors or warnings. Let me know if this library is useful for you, or if there are any other features you'd like to see added or changed. Thanks! Link: JavaScript Regex Syntax Highlighter.