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.

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.

Sorry, that's right. Since we're treating the contents of this script as a string, the JSON string is itself stringified from the perspective of the translator (as opposed to the raw JS we see via View Source). There's no need for the typeof details === "string" conditional — it just always needs to be run through JSON.parse() twice.

I think I've made all the requested changes, but let me know if there's more that needs doing.

Is any more work needed on this?

I've just committed a fix for the case where the json string includes an apostrophe: the source escapes it with a backslash, which JSON.parse treats as an invalid character. I've added a test for this situation.

(I don't think this needs anything else; I'm just a bit underwater with reviews.

Thanks & sorry for the long wait!