How to use # as part of CoffeeScript heregex?

Question

I'm trying to match the hash fragment of a jQuery Mobile URL like this:

    matches = window.location.hash.match ///
        #                   # we're interested in the hash fragment
        (?:.*/)?            # the path; the full page path might be /dir/dir/map.html, /map.html or map.html
                            # note the path is not captured
        (\w+\.html)$        # the name at the end of the string
        ///

However, the problem is that the # symbol gets chopped from the regex in the compiled JS file because it's treated as the start of a comment. I know I could switch to a normal regex, but is there any way to use # in a heregex?

Answer 1

Escape it in the usual fashion:

matches = window.location.hash.match ///
    \#                  # we're interested in the hash fragment
    (?:.*/)?            # the path; the full page path might be /dir/dir/map.html, /map.html or map.html
                        # note the path is not captured
    (\w+\.html)$        # the name at the end of the string
    ///

That will compile to this regex:

/\#(?:.*\/)?(\w+\.html)$/

And \# is the same as # in a JavaScript regex.

You could also use the Unicode escape \u0023:

matches = window.location.hash.match ///
    \u0023              # we're interested in the hash fragment
    (?:.*/)?            # the path; the full page path might be /dir/dir/map.html, /map.html or map.html
                        # note the path is not captured
    (\w+\.html)$        # the name at the end of the string
    ///

But not many people are going to recognize \u0023 as a hash symbol so \# is probably a better choice.

Answer 2

Implementer here. Heregex comments are removed altogether with whitespace using a simple regex (/\s+(?:#.*)?/g), so any non-whitespace character before # (or placing it at the very beginning) works.

$ coffee -bcs
  /// [#] ///                      
  /// (?:#) ///
  ///#///       

// Generated by CoffeeScript 1.2.1-pre
/[#]/;

/(?:#)/;

/#/;