I am reading a Regular Expression Cookbook by Jan Goyvaerts and Steven Levithan. It’s a truly excellent book on a subject, with an incredible level of attention to details. I am only half-way through the book, but have already learned few things about regular expressions – both general and javascript-related ones.

One thing I noticed missing in the book was a mention of whitespace character class (\s) discrepancies in current ECMAScript implementations. Cookbook rightfully explains that \s in Javascript matches any character defined as whitespace by the Unicode standard. What it fails to mention is how horribly this rule is actually implemented in modern browsers. While most of the implementations correctly handle ASCII whitespace characters, such as – U+0020 (Space), U+000B (Vertical Tab) and U+000A (Line Feed) – there’s much more chaos in anything above U+2000 (EN QUAD) point.

In practice such non-conformance can lead to surprising results when implementing something like trim function. If trim were to utilize \s, than it could miss quite common characters like U+00A0 (No-Break Space); In fact, trim used in jQuery or Prototype uses exactly that – standard whitespace character class (\s) – and so fails with any of these troublesome characters. One of the solutions, of course, is to replace \s with a custom character class, e.g.: – [\u0009\u000A\u000B\u000C\u000D\u0020\u00A0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029]

This topic comes up once in a while on comp.lang.javascript and there have been some efforts to document these discrepancies. I wanted to make a simple table of modern browsers compliance and used a test provided once by Richard Cornford (also available online for anyone to try it out).

Here’s a table demonstrating above mentioned deviations. It’s good to see Safari 4+ and Chrome 2+ conforming to specs fully. Hopefully, upcoming versions of Firefox will also take care of the remaining “failures”.

Tests for Firefox, Safari and Opera were performed on Mac OS X (10.5.8); IE and Chrome – on Windows XP Pro SP2 (via VMWare); and Konqueror – on Ubuntu 9.04 (via VMWare)

Edit (28/09/2009)

Clarified operating systems (and their versions) used for testing; Aligned characters in a table by code point; Updated Opera to 10RC, added Chrome 3 to results, combined FF columns into one, since they are the identical; Sorted table by code point. Thanks to Dr J R Stockton and Luke Smith for suggestions.

Edit (04/09/2009)

Updated Opera 10RC to Opera 10 (Thanks to Garrett Smith for test); tested and updated table with results of Safari 2.x and older 3.x versions; fixed a bug in a testcase where `char` identifier (one of future reserved words as per ES3) would prevent script parsing in Safari 2.x