const grandchild = Router()
    .get("/", (req) => req)
    .all("*", () => "not found grandchild");

const child = Router()
    .get("/", (req) => req.params.bar)
    .use("grandchild/:name", grandchild)
    .all("*", () => "not found child");

const parent = Router()
    .get("/", () => "parent")
    .use("child/:bar", child)
    .all("*", () => "not found parent");

parent
    .fetch({
        url: "http://localhost/child/kitten/grandchild/mitten",
        method: "GET",
    })
    .then(console.log)
    .catch(console.error);