I want to dynamically change the uploads destination based on a string I get from req.body.slug, so I am including multer inside the route like so:

const storageMulti = multer.diskStorage({
    destination: initialDestination,

    filename: function (req, file, cb) {
        cb(null, Date.now() + "-" + file.originalname);
    },
});

const uploadMulti = multer({ storage: storageMulti });

router.post("/multiupload", (req, res) => {
    const categoryFolder = req.body.slug ? req.body.slug : "all";

    const updatedStorage = multer.diskStorage({
        destination: function (req, file, cb) {
            cb(null, `./frontend/public/gallery/${categoryFolder}`);
        },
        filename: function (req, file, cb) {
            cb(null, Date.now() + "-" + file.originalname);
        },
    });

    // Use multer middleware with updated destination
    const updatedUploadMulti = multer({ storage: updatedStorage });

    // Use multer middleware with updated destination
    updatedUploadMulti.array("images")(req, res, (err) => {
        if (err) {
            return res.status(400).send("Error uploading files.");
        }
        // Access uploaded files via req.files array
        console.log(req.files);
        res.send("Images uploaded successfully.");
    });
});

That works as far as the uploading goes, the issue is that req.body.slug is undefined unless I change the route definition to include multer, which goes like so but is not acceptable because I want to change the upload folder based on req.body.slug:

router.post("/multiupload", uploadMulti.array("images"), (req, res) => { // if I do this then I do get req.body.slug but this is not acceptable

I am sending data from an RTK Query Mutation if that makes any difference:

const toUpload = new FormData();
            selectedImages.forEach((image) => {
                toUpload.append("images", image);
            });
            toUpload.append("slug", "white-shirt");
            await upload(toUpload);
            toast.success("Images uploaded successfully");