what if the key already has a trailing slash?

These are static strings, it would be /foo/ and /foo//. Handling it felt like the complexity outweighed the use since there are no uses of it currently. It would allow for /foo/ and /foo//.

That being said, I do something like

} else {
  key =  key.replace(/\/?$/, '/?');
  simple[key] = value.url;
}

which would force an optional trailing slash (e.g. /?) on all simple routes

I think it'd be good to consistently support both schemes with and without trailing slash. Stripping trailing slashes when loading the input and when handling a request (like in your first version) might be the easiest way to do this.

I think it'd be good to consistently support both schemes with and without trailing slash.

makes sense

pushed an update, wdyt