I'm not sure whether the attr() function is still needed, or what to do about the unused doc and url params that Travis doesn't like. I'd be happy to clean up further if someone can advise me.

Thanks for the suggestions. I've cleaned up the code in accordance with them. The JSON.parse() problem is weird: because the source string is stringified (with escaped slashes etc.), I have to apply JSON.parse twice to get it into an object. If there's a cleaner way to achieve this I'd love to learn it.

attr and text are no longer needed. The functions will work without the url parameter, but I'm pretty sure detectWeb does need doc so we'll need to escape the eslint rule there.
There was also something wonky about the tests -- somehow they had duplicated which caused the linter to fail.