Node, Express 4 - Regex for routing. Alpha or Alphanumeric including hyphen but not purely numeric

Question

I am trying to build a regex that will match any combination of numerals (0-9), alpha characters and hyphens, but not purely numeric, for use in routing. The simplest example I can give is the following..

router.param('slug', function(req, res, next, slug){
     req.slug = slug;
     next();
}
router.get(':slug((?=[a-zA-Z-])[a-zA-Z-\d]+)', function(req, res){
     res.send(req.slug);
}

The logic behind the regex has been tested at regex101.com

(?=[a-zA-Z-])[a-zA-Z-\\d]+

The idea is a positive lookahead to match at least one of az, AZ or -, and then a match for az,AZ,0-9 in any combination.

Except it doesn't work in express. It will match "h", "h-", "h-9", but not with "9-" or "9a". Furthermore, the slug argument in the param call is empty when it does match. I am stumped. I suspect it might be some escaping issue with the regex string?

Here is a reference to the docs for the param call. http://expressjs.com/en/api.html#router.param

Any help appreciated.

Update: I think it has something to do with there being no capture group in the regex..

Another update: the following regex has a capture group, works at regex101.com, but no dice with express...what am I missing here?

(\\d*[a-zA-Z-][a-zA-Z-\\d]*$)+

Third update: express is calling this library https://github.com/pillarjs/path-to-regexp , which helpfully points out I should be escaping backslashes. I have edited the post to reflect this. The library itself is turning this

(\\d*[a-zA-Z-][a-zA-Z-\\d]*$)+

into this..

^\/(?:((\d(.*)[a-zA-Z-][a-zA-Z-\d](.*)$))+)\/?$

Thanks

Answer 1

This should do it:

(?!\\d+$)[a-zA-Z-\\d]+

Matches:

foo-123 123-bar foobar

Does not match:

123456