Lookbehind assertions in V8 regular expressions

It seems to have gone unnoticed by the good news.



V8 developers have actively started to add lookbehind assertions to regular JavaScript expressions.



In Google Chrome Canary, you can already test with the flag:

')

chrome.exe --js-flags="--harmony-regexp-lookbehind"



This month comes the sixth version of Node.js, based on V8 5.0, and you can also include lookbehind support in it:



node --harmony_regexp_lookbehind



If you can’t wait at all, you can test it on already emerging RC:



nodejs.org/download/rc



I tested the positive and negative variants in the example from the article:







It is worth paying attention to two features mentioned by the authors:



1. Unlike Perl, both lookbehind variants support variable-length expressions.



2. Developers took the path of .NET and in another feature - an unusual (for a start) procedure was established for storing subexpressions and internal links.



PS Innovation has moved to the flag stage - es_staging .