Block Regular Expressions (Heregexes) support interpolation.
Block Regular Expressions
Similar to block strings and comments, CoffeeScript supports block regexes — extended regular expressions that ignore internal whitespace and can contain comments and interpolation. Modeled after Perl's /x modifier, CoffeeScript's block regexes are delimited by /// and go a long way towards making complex regular expressions readable.
This coffeescript code:
name="hello"
test=///#{name}///
compiles to
var name, test;
name = "hello";
test = RegExp("" + name);