I am trying to update some value in my database using python and mongoose (mongo wrapper library). The value I am trying to update is contained in an array (filename).

Full method

module.exports.updateCampground = async (req, res) => {
    const { id } = req.params;
    const campground = await Campground.findByIdAndUpdate(id, { ...req.body.campground });
    const imgs = req.files.map(f => ({ url: f.path, filename: f.filename }));
    campground.images.push(...imgs);
    await campground.save();
    if (req.body.deleteImages) {
        for (let filename of req.body.deleteImages) {
            //logs cloudinary conataining uploader, still uploader is undefined
            console.log(cloudinary,cloudinary.uploader); 
            await cloudinary.uploader.destroy(filename);
        }
        await campground.updateOne({ $pull: { images: { filename: { $in: req.body.deleteImages } } } })
    }
    req.flash('success', 'Successfully updated campground!');
    res.redirect(`/campgrounds/${campground._id}`)
};

This works

const deleteImg = req.body.deleteImages
await campground.updateOne({ $pull: { images: { filename: { $in: deleteImg } } } })

and removes the item however when I do just this it doesn't

await campground.updateOne({ $pull: { images: { filename: { $in: req.body.deleteImages } } } })

Why do I need the const to work? Is it some javascript thing?