Defining routes within exports vs. above it Node.js

I've come across two different methods of defining routes in Node.js:

Method #1:

router.get("/", (req, res, next) => {
    res.render("index", { title: "ABC" });
});
module.exports = router;

Method #2:

module.exports = (() => {
    router.get("/", (req, res, next) => {
        res.render("index", { title: "ABC" });
    });
    return router;
})();

I was curious, what's the main difference between these two? And, is there a major reason why one method is preferred over the other? Thanks!

via user3781239