It's been a while since I worked on regexs in JavaScript, but generally the way you do this in most programming languages is to build the regex as a string and then pass it into the regex engine.

Javascript’s regular expression library is becoming world class, guaranteeing that the odd little pattern language will likely be around for generations to come.

The latest JavaScript specification standardizes a well-balanced and thoughtful set of features, including the built-in global Iterator, new Set methods, improvements to regular expressions, and more.