// Display Author create form on GET.
exports.author_create_get = function(req, res) {
    res.send("NOT IMPLEMENTED: Author create GET");
};

// Handle Author create on POST.
exports.author_create_post = function(req, res) {
    res.send("NOT IMPLEMENTED: Author create POST");
};

Why does create have post and get? Isn"t create a post method? Can
explain the following comments.

// Display Author delete form on GET.
exports.author_delete_get = function(req, res) {
    res.send("NOT IMPLEMENTED: Author delete GET");
};

// Handle Author delete on POST.
exports.author_delete_post = function(req, res) {
    res.send("NOT IMPLEMENTED: Author delete POST");
};

Why does delete have post and get??

// get
router.get("/book/create", book_controller.book_create_get);

// 
router.post("/book/create", book_controller.book_create_post);

Thank you!